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Characteristics and DEV of AK Geothermal Resources 1983
SF.07.OF CHARACTERISTICS AND DEVELOPMENT OF ALASKA'S GEOTHERMAL RESOURCES Dr.John W.Reeder,GeologistAlaskaDivisionofGeologicalandGeophysical SurveysP.0.Box 772116 Eagle River,Alaska 99577 David Denig-Chakroff,Project Manager Alaska Power Authority 334 West 5th Avenue Anchorage,Alaska 99501 INTRODUCTION Alaska has an abundant supply of geothermal resources including over 100 surface manifestations such as hot springs,fumaroles,mud pots,and wells.The use of these resources for health and recre- ational purposes is well documented in historic records.In more recent times,direct uses have been expanded to include space heat- ing in lodges,cabins,and greenhouses.Elsewhere in the world, geothermal resources have been used successfully for many commer- cial applications including electric power generation.The first geothermal power plant was established in Italy in 1906.Over the past several decades,geothermal heat has emerged as a commercial competitor with other forms of energy for both electrical gen- eration and a variety of direct-use applications. An important consideration in geothermal development is that power facilities or direct-use applications must be located near the resource.Due to its potential for heat losses,geothermal energy cannot be transported great distances.Although Alaska has an abundance of geothermal resources,there are only a few areas where the resources occur close to a potential energy market.Conse-quently,any plans.for geothermal development in Alaska must be based on both the nature of the resource itself and on the economic feasibility for its development. This paper presents an overview of the nature and occurrence of geothermal resources in Alaska and a discussion of their develop- ment and potential for development.It also presents a summary of the Unalaska Geothermal Project and discusses its potential for development as the first geothermal power project in the State. THE RESOURCE AND ITS DEVELOPMENT With respect to the nature of the resource,the characteristics of the heat source and of the reservoir are important.Two generic types of geothermal resources have been recognized based on the 8321/350 Page 1 origin of heat that drives their convective circulation systems. These generic systems,in turn,correspond to high temperature(i.e.,392°F or greater)versus moderate or low temperature resources.In addition,the reservoir can be large,moderate,or small in size and usually is within four miles depth.Geothermal fluids can also be classified on the basis of their geochemical and/or geophysical character.For example,geothermal systems canbedry-steam dominated,wet-steam dominated,or more commonly water dominated.The water dominated systems are usually characteristic of the moderate or low temperature resources,and the steam dom- inated systems are for all practical purposes restricted to the high temperature resources.The recognition of these contrasting types of geothermal resources provides a fundamental basis for the serious planning and evaluation of specific geothermal development projects.If the nature of the resource or even its existence is unknown,then serious geothermal development plans are impossible to undertake! The most common utilization of geothermal energy is the "location intensive"small scale use of hot water for various "direct heat" applications.A number of Alaska's thermal spring sites have been used for recreation use,while a few have been used to heat dwell- ings,bath houses,and greenhouses (e.g.,Bell Island,Chena, Circle,Goddard,Manley,Melozi,Pilgrim,and Tenakee Springs). The "location intensive"character of such resources is principally caused by the economic difficulty in transporting such resources.Considering the remoteness of most geothermal sites in Alaska,the development of such resources will probably need to wait until Alaska's energy demand greatly expands.Summer Bay warm springs near Unalaska might be a near-future exception. Ground water at depth can be quite warm due to the heat flow from the Earth's interior,whether hot igneous rock exists or not at shallow depths in the region.Such ground-water bodies might existinlargesedimentarybasinsthatoccurthroughoutalargepartof Alaska.Smaller ground-water reservoirs might also exist in frac-ture zones within metamorphic and igneous (plutonic)rocks that also occur throughout the State.If fractures extend to the sur- face for both situations,then the ground water can circulate to the surface or at least to shallow warm-water reservoirs by means of a density-driven convective system.The widespread hot spring occurrences throughout Alaska's Interior,Seward Peninsula,and Southeast Alaska appear to be principally related to such con-vection in fractures related to igneous (plutonic),some metamorphic,and very limited sedimentary rocks (Waring,1917;andD.G.G.S.,1983). Typically,the regions of deeper hot-water reservoirs where moder- ate temperatures can occur will be overlain by shallower,cooler aquifers that contain water slightly under boiling temperature.Such shallow aquifers would be more likely found if shallow 8321/350 Page 2 sedimentary rock exists in the region in contrast to normally denser metamorphic and plutonic rocks.At Pilgrim Hot Springs near Nome,a shallow aquifer with temperatures near the boiling .temperature occurs in sedimentary rock,which is easily located and produced with volumes and temperatures suitable for space heating or other similar direct applications.This shallow reservoir, which is at depths of less than 100 feet,can produce over 300 GPM artesian flow at 194°F with existing wells that were drilled with State funds.Based on the temperature gradient of these wells,it has been interpreted that the deeper reservoir exists at a depth of about 5000 feet and at a temperature of 302°F (Economides and oth-ers,1982). Such shallow geothermal resources (i.e.,normally at depths of less than 500 feet)are often accessible by typical water-well drillingrigsasopposedtothedeeperreservoirs(i.e.,normally at depthsof4,000 to 6,000 feet)with higher temperatures.The moderate temperatures at the deeper reservoirs are attractive,but the ulti- mate cost associated with drilling up to 6,000 foot wells in remote locations for a resource best suited for just direct utilization such as space heating is discouraging.These moderate temperature resources are amenable to electrical generating production through binary power generation,in which a secondary working fluid is vaporized by the hot water and then the organic steam turns the turbines.This approach unfortunately is expensive. Large-scale geotherma)electrical power development projects require temperatures normally in excess of 392°F for efficient. operation.Such high temperature geothermal systems are almost exclusively associated with igneous heat sources.The classic major geothermal systems around the world,such as those at Wairakei,New Zealand;at the Geysers of California,U.S.A.3;and at: Larderello,Italy are all associated with young (i.e.,less than 1millionyearsold)igneous systems of a particular type,that is those consisting of a rhyolitic magma at shallow depths that were produced from the melting of shallow crust.By contrast,most other volcanic and/or plutonic igneous occurrences that do not consist of rhyolitic melts do not have associated high temperature hydrothermal systems.Rhyolitic rocks are lacking for a majority of Alaska's 55 plus active volcanoes,which are located in the. Aleutian arc.Thus,Alaska's active volcanoes are most likely associated with low to moderate temperature geothermal systems than with high temperature systems if such geothermal systems even exist.Nevertheless,Alaska's andesitic volcanoes may be underlain by "trapped"magma that has risen from great depths.Such magmabodiesmightserveasasignificantheatsourceforlargemoderate- temperature and with luck maybe even high-temperature geothermal systems, 8321/350 Page 3 THE UNALASKA GEOTHERMAL PROJECT The Makushin Volcano region of Unalaska Island is typical of these andesitic volcanic systems.Prominent fumarole fields were observed in this region in 1980 (Reeder,1982).In 1981 the Alaska Legislature appropriated $5 million to be administered by the Alaska Power Authority for geothermal drilling and exploration at Makushin Volcano.The Power Authority selected Republic Geothermal,Inc.of Santa Fe Springs,California to be the consultant to plan and coordinate the exploration and drilling program.The program consisted of three _phases.Phase Iactivitiesincludeddatareviewandsynthesis;technical planning; land status determination;permitting requirements;acquisition of baseline environmental data;geological,geochemical,and geophysical investigations and mapping;and the drilling of three temperature gradient holes.Phase II activities included continued and more extensive testing of the geothermal resource,the drilling of a fourth temperature gradient hole,and an_electrical resistivity survey to delineate the extent of the reservoir. Under Phase I,the first three temperature gradient holes were drilled in 1982 to depths of 1500 feet and encountered temperaturesofupto383°F (195°C).Two of the holes indicated a close prox- imity to geothermal resources below,while the third appeared to be on the fringe of the geothermal system.The Phase I final report was completed in 1983 concluding the strong possibility of a water-dominated geothermal system in excess of 480°F (250°C)on the eastern flank of Makushin Volcano at a depth of less than 4,000 feet. Phase II was initiated in the Spring of 1983.The exploratory well was started in early June.After numerous delays caused by diffi- cult drilling conditions,on August 25,1983,the well encountered a fracture zone from 1,946 to 1,949 feet containing a substantial geothermal resource.Although the exploratory well tapped the res- ervoir by means of a large fracture within plutonic rocks,whicharecommonthroughouttheregioninbothplutonicandvolcanicrocks(Reeder,1985),the actual reservoir is probably located immediately beneath the Makushin volcanic!pile within fairly perme- able brecciated rocks.Initial well -testing confirmed a wa- ter-dominated geothermal system with a 'steam cap and bottomholetemperatureandpressureof379°F (195°C)and 478 psi respective- ly.The onset of inclement weather prevented further resource testing during the 1983 field season. Phase III of the project was conducted in 1984 and consisted of further well testing and reservoir analysis as well as drilling a fourth temperature gradient hole and conducting an electrical resistivity survey.The temperature gradient hole,drilled in an area that would be more accessible to development than the explora- tion wellsite,showed no indications of the presence of a similar 8321/350 Page 4 geothermal resource.The electrical resistivity survey revealed that the site of the current exploration well is the most accessible site where significant geothermal resources are likelytobeencounteredatareasonabledepth.Flow tests and reservoiranalysesconductedin1984indicatethatasinglecommercial-size well located near the current exploration wellsite could produce between 1.0 and 1.5 million Ibs/hr of fluids.A calculation of the estimated reserves reveals volumes of at least three-quarters of acubicmile(Economides and others,1985).These figures indicate that the resource is capable of meeting the current and projected power needs of the island for hundreds of years. However,the existence of a prolific geothermal resource by itself does not justify development of a geothermal power project.That decision must be made based on an analysis of economic feasibility. This means forecasting population,commercial,and industrial growths,power demands,and fuel prices and determining the costs and benefits of a potential project.In the case of Unalaska this may not be an easy task.Unalaska has long been dependent upon the ups and downs of the fishing and crabbing industries.Its power requirements,likewise,follow this cyclical trend.Power demand may range from a peak of 13 MW at the height of a good fishing sea- son to an average of 2 to 3 MW during the off-season.In recent years,Unalaska has attempted to diversify its economy with the development of marine support facilities,a bottomfish industry and,most recently,tourist trade.In addition,the U.S.Coast Guard is considering the island as the site for a large search and rescue facility and the petroleum industry could use Unalaska as a staging area for offshore oi]development.Whether these ventures will succeed and result in an increase and/or stabilization of electrical loads remains to be seen. A geothermal power plant at Unalaska would have to be located at the site of the resource which is 15 miles west of the communities of Unalaska and Dutch Harbor in a remote,roadless,rugged terrain. It is anticipated that construction of a 10 MW power facility including a road and transmission line would cost at least $40 million.A detailed feasibility analysis is needed to determine whether the cost and dependability of power from such a facility will:compete with the existing diesel power generating systems. CONCLUSION A significant and impressive quantity of geothermal resources occur in Alaska,capable of large and small scale development and both direct use and power generation.However,geothermal energy devel- opment is often limited by the remoteness of its occurrence and the availability of a potential energy market.Consequently,any pros- pects for geothermal energy development should be carefully analyzed in terms of the nature and capability of the resource as well as the economic feasibility for development.Recent advances 8321/350 Page 5 in technology and worldwide successes in geothermal resource devel-opment assure geothermal energy a role as a viable competitor among the variety of energy options and alternatives.With Alaska's abundance of geothermal potential,this alternative deserves serious consideration. REFERENCES Division of Geological and Geophysical Surveys of the Alaska Department of Natural Resources,compiler,1983,"Geothermal re- sources of Alaska":National Oceanic and Atmospheric .Administration,U.S.Government Printing Office,1 plate. Economides,M.J.,Ehlig-Economides,C.A.,Kunze,J.F.,and Lofgren,B.,1982,A fieldwide reservoir engineering analysis of the Pilgrim Springs,Alaska,geothermal reservoir:Proceedings of the Eighth Workshop of Geothermal Reservoir Engineering,Stanford Geothermal Program SGP-TR-60 Report,Stanford University,pp 25-30. Economides,M.J.,Morris,C.W.,and Campbell,D.A.,1985,Eval- uation of the Makushin geothermal reservoir,Unalaska Island:Pro- ceedings of the Tenth Workshop of Geothermal Reservoir Engineering, Stanford Geothermal Program SGP-TR-62,Stanford University,in press. Reeder,J.W.,1982,Hydrothermal resources of Makushin Volcano re- gion of Unalaska Island,Alaska:Transactions Third Circum-Pacific Energy and Mineral Resource Conference,American Association of Petroleum Geologist Circum-Pacific Series,pp.441-450. Reeder,J.W.,1985,Fault and volcanic dike orientations for the Makushin Volcano region of the Aleutian arc:Proceedings of the International Symposium on Recent Crustal Movements of the Pacific Region,held February 9-14,1984,at Victoria University, Wellington,New Zealand,Royal Society of New Zealand Bulletin,in press. Waring,G.A.,1917,Mineral springs of Alaska:U.S.Geological Survey Water-Supply Paper 418,114p. 8321/350 :Page 6 Geothermics,Vol.13,No.3,pp.241 -264,1984.0375 -6505/84 $3.00 +0.00 Printed in Great Britain.Pergamon Press Ltd. ©1984 CNR. GEOTHERMAL DEVELOPMENT IN ALASKA:AN ENGINEERING AND GEOLOGIC ANALYSIS M.J.ECONOMIDES and G.N.ARCE University of Alaska,Fairbanks,AK 99701,U.S.A. (Received May 1983,accepted for publication September 1983) Abstract-In spite of the vast geothermal potential within the state of Alaska,the economic feasibility is tenuous.Of the five sites examined in this paper,only Tenakee and Summer Bay have even marginal attractiveness for direct utilization.The geothermal reservoirs located at Copper Valley and Makushin Volcano may be feasible for power generation in the near and intermediate future.To make geothermal development feasible,an increase in the population/industrial base would be required,or a consolidation of the present power users.In general,the economic prospects of geothermal power development in Alaska are not attractive at this time,with the exception of Unalaska Island.FFFFTUNOKARxhNO25gaeCHANPOSoRShtaudbetenathaedNOMENCLATURE annual distribution costs ($) annual fixed costs ($) annual labor costs ($) annual maintenance costs ($) costs per thousand BTU ($) heat capacity (BTU/Ib °F) annual costs of installed insulated piping system ($/mile) annual pump costs ($/mile) cash flow after taxes ($) cash flow before taxes ($); total outside diameter (including insulation)(in.) outside diameter of steel pipe (in.) inside pipe diameter (in.) depreciation ratio of total costs for fittings and installation to purchase cost for new pipe enthalpy rate (BTU/h) ambient (outside)heat transfer coefficient (BTU/h ft?°F) inside heat transfer coefficient (BTU/h ft?°F) total heat load for a town (BTU/h) interest rate investment ($) number of years of a viable project conductivity of insulation (BTU/h ft?°F/ft) conductivity of steel (BTU/h ft?°F/ft) annual fixed charges including maintenance expressed as a fraction of initial cost for completely installed pipe length (ft) mass flow rate (Ib/h) a constant with value dependent on type of pipe.For steel pipes,n =1.5 pump power requirement (kW) town population pump flow rate,gallons per min (GPM) rate of heat transfer (BTU/h) annual revenues ($) ambient temperature (°F) entering temperature (°F) exiting temperature (°F) overall heat transfer coefficient (BTU/h ft?°F) purchase cost of new pipe per foot of pipe length if pipe diameter is 1 in.($/ft) 241 242 M.J.Economides and G.N.Arce INTRODUCTION Alaska potentially contains some of the largest geothermal resources in the United States. However,geothermal development is hindered by the remoteness of the reservoirs from population centers and the small size of Alaskan markets.These factors may render economic exploitation difficult. Five sites in Alaska are examined (Fig.1).They are:Tenakee,Copper Valley,Pilgrim Springs (Nome),Makushin Volcano (Unalaska)and Summer Bay (Unalaska). PRUDHOE BAY @ PILGRIM SPRINGS CANADA FAIRBANKS @ «a MT.McKINLEY COPPER VALLEY ANCHORAGE (=)oo TENNONEESSPRINGS),©SITKA 8 MT. MAKUSHINofoesSUMMER BAY Fig.1.Selected geothermal sites in Alaska. In order to evaluate the geothermal potential of each site,an analysis of those variables pertinent to development are examined.A general discussion of pumping and piping costs in Alaska are presented,along with analyses of transportability factors and heat losses.Economic models for direct heating systems and power generation are also described.In addition,the geological and geochemical characteristics of each site are discussed.These engineering, economic and geologic data are then synthesized to form a comprehensive evaluation of the geothermal potential of each site. THE ECONOMIC AND ENGINEERING MODELS Two economic models are used in the evaluation of the potential of geothermal development in Alaska.For direct utilization the required cost per thousand BTU (C,,,7,)is calculated under a 20%rate of return to.the prospective utility company.The possible selling of geothermal fluids would be unique to Alaska since there is no past history of town-wide heating systems. Geothermal Development in Alaska 243 Almost all of the home and business heating is done either by the combustion of fuel oil or wood.No alternatives to geothermal heating are envisioned on town-wide scales. For power generation,though,the present trends are for the creation of unitized grid systems.For example,on Unalaska Island,while there have been several power generators in operation,the city is installing a grid system that would encompass all users.Hence,the model used in this paper is to compare the rates of return of geothermal power generation versus the rates of return of diesel generation,assuming single utility,single grid system for each town. This comparison is useful since several towns are contemplating new power generation schemes that would support the new unitized electric distribution systems.The geothermal potential thus becomes important as a competing alternative to diesel generation. In the economic models presented in this paper there is no consideration for tax credits and depletion allowances that have been available in the U.S.A.in the past.The present policy of the federal administration is not clear.Further,in Alaska,the land status of many of the contemplated sites is not yet resolved.Much of the land could either be conveyed to native corporations under the Native Settlement Act or could be removed from further consideration for development,if Federal Fish and Game Agencies were to reclaim certain sites as Game Preserves.Hence,the uncertainty of government regulations and land status makes the following economic evaluation necessarily conservative. Multiple uses of the geothermal fluids are not considered in this analysis.The geothermal sites in Alaska are,normally,at a long distance from small communities.Hence,if geothermal power generation were to be utilized then an effort for ''all-electric'?homes may have to be undertaken in order to justify the project.This would necessarily undercut the possibility for multiple uses of the geothermal fluids.Major industry development is not contemplated.As a result,geothermal power plants in conjunction with the transportation of hot water for space heating cannot be envisioned in Alaska at the present time. ECONOMIC EVALUATION OF DIRECT HEATING SYSTEMS The economic scenaria envisioned are:(1)a state appropriation to initiate the project and (2) a private consortium to raise appropriate financing. The two options differ significantly.In the first case,a publicly run facility does not pay taxes,nor does it (necessarily)require a rate of return.Private ventures are subject to taxes and they have to earn an appropriate rate of return. Two quantities are required to prove or disprove the attractiveness of a project.These are the capital investment and annual operating costs.The calculated price will then be compared with present non-geothermal costs. The capital investment consists of the pumping units and the drilling costs of the wells.The in-town distribution system will be treated as an annual cost.The piping costs will also be presented as an annual cost. The purchase costs of the pumps depend on the flow rate and the pump head.Since the piping and pumping costs have identified an optimum pipe diameter,the selection of pump size (head)is also determined.The distance of the geothermal site to the market will indicate the number of pumps (or pumping stations). The operating costs consist then of pumping costs,piping costs,in-town distribution costs, maintenance costs,labor costs and fixed costs. Two engineering issues need evaluation next:(1)the pumping and piping and their associated costs and (2)the pipeline heat losses and flow rate requirements under Alaskan climatological conditions. 244 M.J.Economides and G.N.Arce Annual costs of pumping and piping The annual power costs required to pump the geothermal fluids per mile of pipeline (and assuming 130%load factor and 25¢/kWh)may be given by: Coump =Pm X 1.3 x 24 (h/day)x 365 (day/year)x 25¢/kWh (1) Then: Coump =2.85 x 10°P,,(2) =34.6 h.g {GPM}(3) The annual costs for the piping may be obtained from a correlation supplied by Peters and Timmerhaus (1980): Coie =(1 +F)XG"K,(4) where: Cyine =(in the equation above)cost for installed insulated piping system as dollars per yearperfootofpipelength.The value is in uninflated dollars (i.e.they are based on their real value at the year of installation). In Alaska,X =$0.65/ft of1 in.diameter pipe,K,=0.20 and F =1.4.Then,eq.(4)may be rewritten for a 1 mile length of pipe as: Ciipe(S/year)=1.64 x 10?di!6)pipe The total annual transportation costs for horizontal pipes would then be the summation of the pumping costs and the piping costs. Hence, Cora)=2.85 X 10°P,+1.64 x 10°d5 (6)total These do not include the initial costs of the pumps at the geothermal sites or the distribution system in-town.Such costs vary for each location and will be dealt with separately. Figures 2 and 3 represent optimization graphs for the total costs.Small diameter pipelines G-----4)2250 GPM 4---_----4 1124 GPM 108 ---_-*562 GPM o----9_225 GPM Ww 107 = Ke wnOo |oO a << =) ESZ 10 4LOST ATT re ee |fe)5 10 15 20 25 PIPE DIAMETER (in) Fig.2.Optimization of annual total costs per mile of geothermal fluid transportation (low flow rates). Geothermal Development in Alaska 245 -----1 16857 GPM o-----9 |1240 GPM *----*5620 GPM ANNUALCOST/MILEfe)Cs)rr a ie)5 10 15 20 25 PIPE DIAMETER (in) Fig.3.Optimization of annual total costs per mile of geothermal fluid transportation (high flow rates). have low construction costs,yet they have much higher pumping requirements due to higher friction losses.Hence,for flow rates of 225 GPM,562 GPM,1124 GPM and 2250 GPM (sufficient for towns up to 2000 people),there is a clearcut minimum cost (Fig.2).For larger flow rates,there is an obvious need for larger diameter pipelines (above 24 in.),in.order to achieve minimum costs (Fig.3). The correlation by Peters and Timmerhaus (1980)is not considered valid for pipelines with very large diameters.Hence Fig.3,dealing with cities of more than 5000 people,is left as it is without a further attempt towards optimization,assuming that the 24 in.diameter pipeline would suffice. The in-town distribution costs will be fairly standardized,i.e.a set footage per user of insulated,main line plus small diameter,branching,insulated pipe.Assuming SO ft of 4 in.line, plus 100 ft of 1 in.line per user,the annual pipe distribution costs are: n P nCus=1.572 (S0,(+F)X4'K,+1.572 (100)(1 +F)X1"K;(7) usingF =1.4,X =$0.65/ftoflin.,n=1.5,K,=0.20 Then Cy,=105.3P,(8) The maintenance costs are treated as a fixed percentage of the pumping unit costs (1 %/year is used). C,maint =0.017 (9) The labor costs are the most difficult to assess.Large units would require full-time employees,while smaller units could not justify such expenditures.Hence the labor costs can only be approximate depending upon whether a municipality may undertake the operation as part of ongoing activities,whether it would be contracted out,or whether a private company would operate the facility.The labor costs are-expected to be 5%of the initial investments. Cy,=0.051 | (10) 246 M.J.Economides and G.N.Arce Finally,the fixed costs are normally assessed at 7%of the investment.Hence, Crp =0.071 (11) The amount necessary to charge for 1000 BTU of delivered heat in order to defray investment and annual operating costs would serve as the gauge of whether direct heating geothermal systems are attractive. The revenues,R,are then obtained by multiplying the annual heat load by the cost per 1000 BTU (Cysru)- PR=1.5%30,000 x 24 x 365 X Cysry/1000 (12) R =9.86 X 10 P,Cyary (13) Equation (13)assumes a load of 30,000 BTU/h for a household (assuming a four-member household).The factor 1.5 accounts for non-domestic uses.This factor has been obtained through spot-check surveys in a number of communities.It varies from 1.2 to 1.8 depending upon local activities. Then,the net cash flow before taxes is: C.F.B.T.=R -Coe -Coump -Cas -C,main Cup Cin (14) If the project is funded by the government,and assuming a 20-year life of the project,then the cost of 1000 BTU may be calculated from the relationship: 20(C.F.B.T.)=I (15) If the project is private,then the cash flow before taxes must be further reduced by the depreciation,D,and then assuming a corporate tax of 48%,the cash flow after taxes will be: C.F.A.T.=0.52(C.F.B.T.-D)+D (16) ump There are several ways to assess depreciation.For simplicity,a straight line,20-year depreciation rate will be used here.Hence, D =1/20 (17) Finally,assuming a 20-year,20%rate of return,the cash flow after taxes must be multiplied by the uniform series present worth factor and equated to the capital investment.Hence, (q+ijy-1=---.-(C.F.A.T,.1aap!)(18) where j is the rate of return (0.20)and j the number of years (20).The uniform series present worth factor is then equal to 4.87 and eq.(18)reduces to: I=4.87(C.F.A.T.)(19) From this relationship and eqs.(17),(16),(14)and (13),one may easily calculate the Cysry for each site. Pipeline heat losses and flow rate requirements under Alaskan weather conditions Certain assumptions are necessary for this set of calculations. (1)Complete mixing within the pipeline is assumed.(This is assured by the high turbulence of the flow.) (2)The heat loss to the surroundings is controlled by the resistance through the pipeline Geothermal Development in Alaska 247 insulation.Hence,the reciprocal of this ''controlling resistance''can be set as equal to the overall heat transfer coefficient. The heat loss equation,through a horizontal pipe,exposed to the atmosphere is Test,20Q=d_,din(d/d)din(d/d)|1 (20) hd;2K eoi 2kin.h, where h;is taken as equal to 200 BTU/h ft?°F [from Kern (1950)]and h,is equal to 3 BTU/h ft?°F.(kK.=0.033 BTUZh ft?°F/ft and k,.,=26 BTU/h ft?°F/ft).Table I contains typicalinssteel dimensions of insulated pipelines in use in Alaska. Table 1.Dimensions of insulated steel pipe (in.) Nominal diameter d,(inside)d,(+steel)d(+insulation) 4 4.026 4.500 12.500 8 7,981 8.625 16.625 12 12.090 12.750 20.750 16 15.250 16.000 24.000 24 23.250 24.000 32.000 For a typical case (8 in.),the values of the individual resistances may be calculated. d 16.625 ===0.010hd200x7.981 din (d/d)_16.625 In (8.625/7.981)2K ee 2 x 26 =0.025 _din (d/d)_16.625 In (16.625/8.625)_nr)an 2 x 0.033 soe 1 1.=-=-=0,33ohn3 Obviously,r,,7:and r.may be readily ignored.The overall heat transfer coefficient,U,can then be calculated: 1 2k.U rs d \n (d/d,)(21) and T.-T Lk,Q =2 i =°n ins (22) In T,Tr,In (d/d.) This heat loss must be equal to the change in enthalpy of the fluid. Ah =mCX{T,-T,)(23) 248 M.J.Economides and G.N.Arce Equations (22)and (23)yield: ih ==ore (24) In T,-T,In (d/d.) Finally, 2nLk,T,=T,+(7,-T.=25oTAexp(ama)(25) Equation (25)is significant since it provides the exiting water temperature,7,,following a path of length Z (in ft)with a flow rate 7 (ib/h)and subjected to an ambient temperature,7,,. The initial wellhead temperature is 7; From eq.(25),the in-town temperature,7,,may be calculated.The same equation allows the evaluation of the limiting distance that water may be pumped in order to deliver a certain temperature. Example |.Calculation of limiting distance (L)in the transportation of geothermal heating Sluids Assume:wellhead temperature,7,=200°F, population (such as Nome),P,=2000, ambient temperature,7,=O°F, pipeline diameter,d,=24 in. k,,,=0.033 BTU/h ft?°F and temperature delivered,7,=170°F. The flow rate requirement for various sizes of population centers may be approximated using an average heat consumption per household and business.For the case of four-member households and a 30,000 BTU/h heating load,the total load for a town is: h,=1.5 °x 30,000 (BTU/h)(26) as explained in eq.(13). The load implied by eq.(26)must be equal to the useful enthalpy output of the heating fluid: Ah =mC,AT (27) where AT is generally taken as equal to 20°F.The latter is considered as a fairly efficient temperature drop in heating systems. Equating A,and Ad and solving for ¢#results in: ti (Ib/h)=562.5P,(28) or,since flow rate is normally measured in GPM,then: 562.5 x 7.48 (gal/ft')x P,m (GPM)=62.4 (lb/ft!)x 60 (s/min)=1,124P,(29) Equation (29)allows the calculation of the heating flow rate requirements for various sizes of population. From eq.(28): m =562.5P,=562.5 x 2000 =1.125 x 10°lb/h Geothermal Development in Alaska 249 Using 4 in.insulation,d =32 in. Then from eq.(25): L =2.53 x 10°ft =48 miles If the ambient temperature were -40°F,then: L =2.09 x 10°ft 39 milesi Therefore,the transportability of geothermal fluids is significantly reduced in the harsh Alaskan climate. ECONOMIC EVALUATION OF GEOTHERMAL POWER GENERATION Geothermal power generation has a priori a limiting constraint.The power plant must be in close proximity to the reservoir.Hence,the construction costs are often large,since they must be assessed on remote and harsh sites. In Alaska,construction and logistical costs are significantly higher than elsewhere in the United States.Drilling costs,because of the cumbersome logistics,are expected to be at least twice the level of established sites such as in The Geysers or in the Imperial Valley. As an example of the logic used in the economic evaluation,a case applicable to Unalaska (Makushin)is presented here. Table 2 presents a best estimate scenario for a 30 MW,geothermal power plant on Unalaska Island revised from the original,presented by Economides ef a/.(1981). Table 2.Capital investment for a 30 MW,geothermal power plant,Unalaska Island Item Number Description Cost Well 6 8000 ft,7%in.diameter (assumed 50%dry wells)$18,000,000 Piping -3000 ft,8 in.diameter pipe,installed 250,000 Road _-3000 ft of service road,18 ft wide gravel,at $200,000/mile 115,000 Generator 55 MW,maximum capacity generator,installed 25,000,000 Transformer station 1 55 MW,at $40/kW,installed 1,833,000 Transmission line 1 11 miles of transmission line overland (helicopter installed),5 miles underwater,$100,000/mile 1,600,000 Road -16 miles of 18 ft gravel road at $200,000/mile 3,200,000 Subtotal ;$49,998,000 Contingency 10%of capital 4,988,000 Total to be depreciated $54,986,000 A conservative estimate of 50%dry holes is assumed.A transmission line,16 miles long,and a connecting 16 mile gravel road are assessed to the cost of a power plant.An average geothermal well,producing 200,000 Ib/h of steam (either superheated or separated)can support a 10 MW,maximum continuous capacity power plant. The operating costs for the same plant were calculated and presented in Table 3. A similar calculation was done for diesel generated power plants,assuming that consolidation of all present units would be a desirable event.A new diesel generating system, supplying 30 MW,,would cost $20.6 million installed (source:General Electric,personal communication). 250 M.J.Economides and G.N.Arce Table 3.Estimated annual operating costs for a 30 MW,geothermal power plant on Unalaska Island Item Description Cost ($1000) Employee compensation Three professionals x $50,000, 25 hourly x $40,000 plus 50%benefits 1725 Wells Maintenance 100 Plant facilities 0.1%of generator cost 250 Piping 20%of pipe cost 50 Transmission line 2%of cost 37 Road 2%of cost 64 Fixed costs 7%of investment 3841 Total annual costs ; 6067 Assuming:labor costs =$40/kW, fixed annual costs =7%of investment, fuel costs =$1.40/gal (363,000 gal/MW,/year)and the total operating costs =$17.9 million. The two options are then compared.The revenues are calculated using 15¢/kWh as the selling price and operating at 75%capacity.Assuming a 30-year straight-line depreciation and a tax rate of 48%,the rate of return is calculated.A summary of the calculation is presented in Table 4. Table 4.Comparative economics of geothermal and diesel power plants on Unalaska (30 MW,) Geothermal ($1000)Diesel ($1000) Revenues 29565 29565 Operating costs ;6067 17888 Depreciation 1829 667 Cash flow before taxes 21669 11010 Minus 48%taxes 10401 5285 Cash flow after taxes (+depreciation)13097 6392 Rate of return (30 years)24.0%31.2% The ''bottom line''comparison is the calculated rate of return.As can be seen in Table 4,the diesel option has a better rate of return than the geothermal option (31.2%vs 24%).Higher capacity plants tend to push the geothermal option closer to the diesel option and eventually they may surpass it,depending on the economic variables applicable to each site. A generalized model has been written and applied to selected geothermal sites in the state.All variables that were presented in the previous example may be changed,including the prospect of a government funded and operated project in which the tax rate is zero. Figures 4-8 include a number of runs using a base case (Fig.4)and changing certain pertinent variables. Figure 4 assumes a private project,15¢/kWh the price for electric power and $1.40/gal the price for diesel.There are two wells per 10 MW,(i.e.assuming 200,000 Ib/h wells,50%dry).In a repeat of the above run,with the price of diesel set at $1.20/gal,the point of intercept shifted to the right,approaching 55 MW,.When the price of diesel was increased to $1.60/gal,the reverse effect was observed,reducing the intercept to 22 MW.. Geothermal Development in Alaska 251 60- 40 x z &5 4Wwy CIRCLES ARE FOR GEOTHERMAL w TRIANGLES ARE FOR DIESELo204 lu|©q oO oT TT qT U v qT '|a v T t t Le oo oe |tT TT | 10 20 30 40 50 60 POWER GENERATION CAPACITY (MWe) Fig.4.Comparison between diesel and geothermal power plants (base case).Tax rate 48%,fuel $1.40/gal. 80> 60 -_- PS =f Z 4044 z CIRCLES ARE FOR GEOTHERMAL W a TRIANGLES ARE FOR DIESEL 5 Ww 205 4 a {0}T T T T |T li Ly T ]7 T U T |TOF T v }T T t J | lo 20 30 40 50 60 POWER GENERATION CAPACITY (MWe) Fig.5.Comparison between diesel and geothermal power plants.Base case,fuel $1.40/gal,power $0.20/kWh. The impact of higher electric prices that the market may bear is shown in Fig.5.Higher revenues,offsetting the high operating costs of the diesel option,render geothermal unfeasible within the 55 MW,market capacity.Figure 6 demonstrates the feasibility of a government sponsored project (0%tax).Finally,Figs 7 and 8 point out the effects of highly successful versus lackluster drilling programs.The first shows the impact of 100%wet (and prolific holes), while the second shows a case in which three wells are required per 10 MW,. In general,the intercept (if any)between the geothermal plant rate of return and that of the diesel powered plant,as shown in Figs 4-8,provides the break-point in plant capacity above which geothermal is economically attractive. 252 M.J.Economides and G.N.Arce 100 = 80 = 60 = Ps z 7 He 40-4 CIRCLES ARE FOR GEOTHERMAL a TRIANGLES ARE FOR DIESELro]"4 uJ <20Py 7 0 TOTTI tt POWER GENERATION CAPACITY (MWe) Fig.6.Comparison between diesel and geothermal power plants.Base case,tax rate 0%,fuel $1.40/gal. 80 - 60 4 2 a &404Fa . ied.7 CIRCLES ARE FOR GEOTHERMAL ©TRIANGLES ARE FOR DIESEL udW204 ©4 (e)T 7 ul qT {7 LJ qT qT |LJ T T T |ul qT 7 qT |qT T qT T | POWER GENERATION CAPACITY (MWe) Fig.7.Comparison between diesel and geothermal power plants (1 well/10 MW,).Wells down 50%,fuel $1.40/gal, power $0.15/kWh. Figure 9 presents a picture of the comparison between the two options for Unalaska (31 MW,)and Copper Valley (21 MW,).These results are approximate.The rates of return are for comparison only;they do not include in-town distribution costs (already there), maintenance and labor. The conclusion is that if these sites could support a market (both industrial and domestic) that would demand those levels of power,then geothermal could be an attractive option if a new diesel generator (for the entire location)were to be installed instead. Geothermal Development in Alaska 253 4o 30 CIRCLES ARE FOR GEOTHERMAL20 TRIANGLES ARE FOR DIESEL RATEOFRETURN%0 LO | 10 20 30 40 50 60 POWER GENERATION CAPACITY (MWe) Fig.8.Comparison between diesel and geothermal power plants (three wells/10 MW,).Wells up 50%,fuel $1.40/gal, power $0.15/kWh. 80-5 --eo tam TNALASKA GEOTHERMALonUNALASKADIESEL -_-eweoe COPPER RIVER GEOTHERMAL ----COPPER RIVER OLESEL704 x z 60- [omg =) - uw 50-7 [a w °407 Ww EK <4x30 205 10 1 0 70 PLANT CAPACITY(MWe) Fig.9.The economic feasibility of geothermal power plants replacing diesel in selected sites in Alaska. SITE DESCRIPTIONS AND EVALUATIONS Tenakee The thermal springs at Tenakee occur in Cretaceous granitic rocks on the eastern shore of Chicagof Island,roughly 75 km southwest of Juneau (Brew and Morrell,1980).High-angle joint sets are common at orientations of NSOE and N40W.Classified as part of the Alexander 254 M.J.Economides and G.N.Arce tectonostratigraphic terrane (Jones ef al.,1981),the intrusive bodies are bordered on the north by Paleozoic hornfels and amphibolite,along with Silurian graywacke and sandstone of the Pt. Augusta Formation.To the south are large plutonic masses of Silurian and Cretaceous age, along with extensive exposures of a Juro-Cretaceous melange consisting of limestone,chert, layered gabbro and serpentinite (Beikman,1980).Preliminary paleomagnetic data in the Craig region of Prince of Wales Island indicate that the rocks have undergone about 35°of counterclgckwise rotation and over 15°of northward movement since late Ordovician to Pennsylvanian time (Berg et a/.,1978). The village of Tenakee Hot Springs,Alaska (photo by M.J.Economides). The Tenakee springs were originally reported to have a total discharge of 22 GPM and a maximum temperature of 41°C (Waring,1917).Subsurface reservoir temperatures recently calculated by Ivan Barnes,using silica and alkali geothermometers,indicate temperatures between 101 and 110°C (Reeder,1982,written communication). This liquid-dominated system may derive its fluids from connate waters associated with expansive sedimentary units located at depth.The prominent joint sets in the granitic rocks provide avenues for the transportation of the heated fluids to the surface.A fault has been postulated to exist south of Tenakee Village beneath the waters of Tenakee Inlet (Loney et a/., 1975;Reeder,unpublished map).If this feature does exist,it may be acting as a no-flow boundary and thus impede southward escape of thermal fluids. Seven shallow test wells drilled during the summer of 1981 encountered cold to warm artesian waters.The warmest waters (38°C)were obtained from the deepest well (55 m),which also had a discharge of 0.5 GPM (Miller,1981). The most obvious consumer of the geothermal resource would be the community of Tenakee. Since the springs are located within the village confines,direct utilization for purposes other than power generation could be accomplished easily. Geothermal Development in Alaska 255 The annual heat load demand for Tenakee is [eq.(26)]: 1.5h,=-=(200)(30,000)(24)(365)=1.97 x 10"BTU The required flow rate is [eqs.(28)and (29)]: m =112500 lb/h =225 GPM This flow rate requires a modest well ( $2,000,000)plus a 225 GPM pump. The required pressure head,assuming 5 miles of 4 in.pipeline network,is: h,(ft)=6.94P,!-5d,-475 =15 ft From Peters and Timmerhaus (1980,Fig.13-40),a3 x 3,3 HP pump would be adequate. Cost is $46,000 (for stainless steel).Then,J =2,000,000 +46,000 =$2,046,000.The revenues and operating costs may then be calculated. R =1.972 x 10'Cusry Coump leq.(1)]=$5.84 x 10°C,,[eq.(8)]=$2.1 x 10° Craint [eq.(9)]=$2.05 x 10° Cy,[eq.(10)]=$1.02 x 105 C;,,[eq.(11)]=$1.43 x 10° C.F.B.T.[eq.(14)]=1.972 x 107 Coury -8-52 x 10° Uf government project. 20(1.972 x 10'Cypry -8.52 x 10°)=$2,046,000 or Cypry =$0.048/1000 BTU This is a good price,assuming.an average 30,000 BTU/h consumption per household, spanning the entire year. If private project. C.F.B.T.=1.972 x 10'Cygry -8.52 x 10°-2,046,000/20 =1.972 x 10'Cyst -9.54 «10% C.F.A.T.=0.52(1.972 x 10'Cypr -9.54 x 10°)+2,046,000/20 =1.025 x 10'Cygne -3.94 x 10° and [eq.(19)]: 2,046,000 =4.87(1.025 x 10'Cyur -3.94 x 10°) Then Cypre =$0.079/1000 BTU This is equivalent to $1.10/gal fuel oil ( 140,000 BTU/gal). The conclusion for Tenakee is that geothermal heating may be equally attractive to fuel oil if one good well could be drilled on the first try.There is no margin for a dry hole. Copper Valley The Klawasi hydrothermal springs occur on the western flank of Mt Drum,30 km east of the 4 i 256 M.J.Economides and G.N.Arce Copper River Basin.Quaternary alluvium and glacial deposits blanket much of the basin,and zones of discontinuous permafrost are located at a depth of 3 m.Isolated windows of Eocene continental sediments are exposed locally.Schist,greenstone,graywacke and shale of Paelozoic to Cretaceous age form the upland areas which border Copper Valley on the north and south. The eastern portion of the basin is underlain by Cenozoic lavas emanating from the Wrangell Mountains (Beikman,1980).Extrusion rates from these volcanoes are about an order of magnitude greater than anything reported from the Cenozoic circum-Pacific,and individual andesitic edifices are among the largest in the world.Isotopic data do not indicate the involvement of abundant crustal material,since the values for Nd (0.5129),Sr (0.7033)and Pb are consistent with mantle numbers.The voluminous production rates have,therefore,been interpreted as indicating a higher rate of magma production or an increase in extrusive versus intrusive magmatism immediately following accretion of the Yakutat Block in southeast Alaska (Nye,1982). The structural framework of the Copper River Basin is dominated by east-west trending orogens which are concave to the south (Alaska Geological Consultants and Geonomics,1975). Two regions of low gravity,the Glennallen and Gakona lows,were found by Andreasen et al. (1964)to trend from Mt Drum into the Copper River Basin.Of the three thermal springs in the Klawasi area (Upper Klawasi,Shrub and Lower Klawasi),two occur near the axis of the Glennallen low.This low may be due to the presence of a thick succession of sedimentary rocks (Reeder et al.,1980). The regional aeromagnetic map of the Copper River Basin suggests that the basaltic and andesitic lavas of the Wrangell massif underlie the mud volcanoes of the Klawasi hydrothermal springs at a relatively shallow depth (Andreasen et a/.,1964).A rapid decrease in the magnetic gradient westward probably indicates that the lavas are thinner and buried at increasingly deeper depths under the alluvium of the basin. The thermal waters emerging at the Mt Drum mud volcanoes were found to have flow rates of 0.3--10 GPM and temperatures of 12--30°C.The silica,potassium,sodium and bicarbonate contents were relatively higher than the contents measured from other mud volcanoes in the Copper Valley region (Nichols and Yehle,1961).Subsurface reservoir temperature have been calculated at 104--157°C and 187°C,based on silica and Na K--Ca geothermometers (I.Barnes,U.S.G.S.). An exploration well was recently drilled at Moose Creek by the Pan American Petroleum Corporation.Located just west of Glennallen on the axis of the Glennallen gravity low,the wellbore penetrated olivine basalt of the Talkeetna formation after passing through over 2200 m of Cretaceous sedimentary units.High pressure water was encountered at a depth of 1646 m in a bentonitic shale horizon (Reeder ef a/.,1980). The hydrothermal reservoirs in the Klawasi area are probably artesian aquifers lying at depths of up to 2 km within the sedimentary sequence.A significant amount of cooling and mixing likely occurs during the upward migration of these fluids (Reeder et al.,1980),especially in their passage through glacial till and permafrost. Possible recipients for geothermal energy include Copper Center (population 213), Glennallen (488)and adjoining areas (750).Summing the populations and assuming an average distance of 16 miles from the Klawasi Springs yields: h,=1.43 x 10''BTU m =815,000 lb/h =1630 GPM Using a 16 in.pipeline: h,=300 ft (elevation +friction) Geothermal Development in Alaska 257 There is a need for four to six wells at a cost of $10 million ($2 million/well).Pump costs (two 8 x 6,125 HP units)=$2.8 x 10°.Then/=$10.3 million. R =1.43 x 10*Cuary Cope =$1.68 X 10° Cyump =$2.70 x 10° C,;,=$1.53 x 10°(this is conservative,the population is scattered) Craim =$1.04 x 108maint Cup =$5.15 x 10° Cig =$7.21 x 108 .F.B.T.=1.43 x 10°Cugry -2.11 x 10°'e)Then 20(1.43 x 10°Cygry -2.73 x 10°)=10.3 x 10° Custy =$1.91/1000 BTU significantly above present prices (one order of magnitude). Pilgrim Springs The thermal activity at Pilgrim Springs occurs in the Pilgrim River Valley on the Seward Peninsula.This valley is a fault-bounded tectonic depression located 75 km north of Nome. Precambrian amphibolites and Mesozoic plutons are the common lithologies in the area,with local exposures of conformable and unconformable (overthrust)Paleozoic carbonates (Hudson,1977).Potassium-argon dating indicates a cooling age for the plutons of 84 m.y. (Turner and Swanson,1981),which suggests intrusive igneous activity in the Upper Cretaceous. A permafrost horizon has also been identified which encloses an area of 1 -1.5 km',and is over 100 m thick. Gravity surveys conducted in the region (Turner and Forbes,1980)indicate that Pilgrim Springs is located near the intersection of two possible fault zones which form the corner of a downdropped basement block.Seismic data imply that normal faulting is presently occurring and this subsidence is further substantiated by surficial geologic mapping.One or more of these faults could provide deep conduits for the geothermal anomaly. In order to explain these geological and geophysical observations,Wescott and Turner (1982) postulate that the Pilgrim River Valley graben represents an incipient rift extending 250 km across the central Seward Peninsula and offshore into the Bering Sea.Based on this hypothesis, the anomalous heat flow in the Pilgrim Springs area is due to tensional tectonics and active rifting. The possible existence of a major rift system is significant for the regional geothermal potential,since extensional tectonics allow for the shallow emplacement of high-temperature magma.A helium soil survey was conducted to test this rift model,and nine out of 11 helium anomalies (which indicate abnormally high heat flow)occur near the proposed rift segments. Furthermore,extensive basaltic fields north of the Pilgrim Springs region have been interpreted as resulting from eruption in a zone of crustal weakness produced by north -south extension (Turner and Swanson,1981).The amount of separation along this proposed rift is less than the widths of the observed Quaternary depressions,since the depressions have been affected by the interaction of normal faulting,subsidence and rifting. The thermal waters emerging at Pilgrim Springs are alkali-chloride fluids with a flow rate of 67 GPM and a temperature of 81°C.Preliminary Na-K -Ca geothermometry of this liquid- 258 M.J.Economides and G.N.Arce dominated system suggests deep reservoir temperatures approaching 150°C (Wescott and Turner,1982). Two 50 m test wells were drilled in 1979,and artesian aquifers were encountered at a depth of 20-30 m.Flow rates were estimated at 200 and 300-400 GPM,respectively,with temperatures of 90°C (Wescott and Turner,1982). During the summer of 1982,deeper exploration wells were completed.The temperature data from these six exploration wells were then graphically plotted to yield temperature vs depth curves (Economides et a/.,1982).The curves display a trend toward a maximum temperature at depths of 40-100 ft (12-30 m),followed by a rapid temperature decrease at depths of 100-250 ft (30-75 m),and finally by a constant geothermal gradient ranging from 1.8 to 2.1°C per 100 ft,down to a depth of 900 ft (270 m).Two deep wells (PS4 and PSS)show temperature trends which would intersect at 155°C and a depth of 4875 ft (1477 m),suggesting that all of the wells overlie a source reservoir which is located at a depth of 4875 ft.The shallow temperature anomaly observed in all the wells suggests that somewhere in the immediate vicinity,hot water is flowing upward through a fault or fissure system.This conduit is inferred to extend vertically from a depth of about 50 ft to the deep source reservoir at 4875 ft. By simple observation,the variables between Pilgrim Springs and Nome are even less favorable than in the case of Copper Valley.There is no apparent need to calculate Cygry. Summer Bay Unalaska Island is the second largest island west of the Alaska Peninsula,in the eastern Aleutian arc.The rocks on Unalaska Island may be grouped into three major categories,which have been correlated with those found throughout the central and eastern Aleutian Islands (Marsh,1982).The oldest and most extensive unit is the lower Tertiary Unalaska Formation. Drewes et al.(1961)described this formation as a thick sequence of coarse and fine sedimentary and pyroclastic rocks interbedded with basaltic,andesitic and dacitic lavas.Graywacke, tuffaceous sandstone and argillite are the common sedimentary rocks,and the entire formation contains abundant alteration products (such as chlorite,pyrite,epidote and albite).The depositional environment of the Unalaska Formation is interpreted to be a perched interarc basin on the summit of the Aleutian ridge,which would account for the intercalated debris flow and proximal turbidite units (Lankford and Hill,1979). Upper Tertiary calc-alkaline plutons comprise the second lithologic category.Three batholithic intrusions and 25 smaller plutons have been mapped (Drewes et a/.,1961).The larger intrusions are commonly zoned with marginal phases as mafic and gabbro.Widely spaced parallel joint sets within the three batholiths are separated by massive unjointed rock. The most abundant intrusive rock type is hypidiomorphic-granular granodiorite,with quartz diorite,quartz monzonite and aplitic granite occurring locally.These intrusive bodies were emplaced by the complex interaction of assimilation,forceful intrusion and stoping mechanisms.Detailed studies on the Captains Bay pluton by Perfit (1977)indicate inward fractional crystallization of a parental andesite or high-alumina basalt.Fractionation took place at shallow depth (less than 20 km),with a temperature between 950 and 1210°C. The final group consists of basalt and andesite flows of the Quaternary Makushin Volcanics which unconformably overlie the older lithologies.Although the thickness of the Makushin Voleanics is not known exactly,it probably does not exceed 1500 m.The volcanics consist of approximately 80%basalt and andesite lava flows,and 20%agglomerate,tuff breccia and flow breccia (Drewes et al.,1961).Lava flows are commonly 5 -20 m thick and may be separated by thin tephra or debris flow horizons.The flows form a radial pattern around the summit of Makushin Volcano,which is now capped by an ice-filled caldera. The first of the two major hydrothermal areas on Unalaska Island is at Summer Bay.These Geothermal Development in Alaska 259 warm springs flow into shallow pools located in a north -south trending glacial valley,roughly 2 km south of Summer Bay and 6 km east of Dutch Harbor.The largest of the thermal springs has a temperature of 35°C and a discharge of 2 GPM.Subsurface reservoir temperatures are predicted to be 60-86°C,based on silica geothermometry (Motyka ef a/.,1981). Several steeply-dipping faults have been identified in this region,and may provide deep- seated conduits for the circulation of meteoric waters.A large normal fault striking N45W and dipping 60-70°south is well exposed along the coast just south of Summer Bay.This fault may be projected across Summer Bay Lake and through the Summer Bay warm spring, although exposures become increasingly poor.Because of this uncertainty,joints trending N45W are highly suspected as controlling the source waters of the springs (Reeder,1981). During 1980,two shallow exploration wells were drilled.Both wells encountered a warm water aquifer in sandy soil at a depth of approximately 13 m,with bedrock at 17 m.Water temperatures were 43 -50°C,with flow rates of 7 and 50 GPM from the 4 in.diameter wells.It is not clear what lithologic unit is acting as a cap for this aquifer,because no significant thickness of impermeable material was detected during drilling.However,a lightly cemented horizon of clay was observed at a depth of roughly 10 m in the wellbore (Dames and Moore, 1980),and this is apparently capping the system. The waters from the two test wells and from the surficial warm springs are chemically very similar.All have chloride and sulfate as their major anions,with sodium and calcium as the major cations.Ratios of Na:Cl,K :Cl,SO,:Cl and Na:K are nearly identical.This suggests that the thermal waters have a common source which undergoes varying degrees of mixing with cold surface waters (Motyka et ai/.,1981). To further delineate the extent and characteristics of the thermal area,several types of geophysical and geochemical studies were undertaken in 1981 (Reeder,1982,written communication).An EM-31 Geonomics survey verified that the N45W joints mentioned earlier are acting as conduits for the warm springs.Schlumberger electric soundings and dipole-dipole resistivity surveys,along with mercury and helium soil surveys,have demonstrated the limited regional extent of the thermal manifestations. The twin communities of Unalaska/Dutch Harbor support a population of 1300,and are located approximately 5.5 miles from Summer Bay.The necessary flow rate would require five wells at a cost of $10 million.Also,two pumps 8 x 6,125 HP at acost of $2.8 x 10°./=$10.3 million. m =731000 lb/h =1462 GPM R =1.28 x 10°Cupre Cyine =$5.77 x 10°(16 in.pipeline) Crump =$1.55 x 10' C,,,=$1.36 x 10° Cc =$1.03 x 10° Cin =$5.2 x 10% Cy,=$7.2 x 10° C.F.B.T.=1.28 x 10°Cy yr -1.39 x 10'Care Then 20(1.28 x 10°Cur 1.75 x 10')=10.3 x 10° and Cyyr,=$0.14/1000 BTU equivalent to $2.01/gal of fuel oil.A government sponsored project may be attractive, depending on the immediate future of oil prices.The figure,thus reached,is very near the present prices on the island.No private investment can be attractive at this time. 260 M.J.Economides and G.N.Arce Makushin Volcano The second major hydrothermal area on Unalaska Island is at Makushin Volcano.In contrast to the small,low-temperature thermal activity in the Summer Bay region,the area around Makushin Volcano contains large hot springs and several fumarole fields (Reeder, 1981).These thermal fields occur in the vicinity of Glacier Valley and Makushin Valley. The summit of Makushin Volcano (photo by J.W.Reeder). Glacier Valley originates on the rugged south flank of Makushin Volcano and trends southwest for about 10 km to sea level.Located 22 km west of Unalaska/Dutch Harbor,the thermal!activity (which includes warm springs,hot springs and superheated fumaroles) emanates from both the Unalaska Formation and the gabbroic plutons which intrude it. Motyka et al.(1981)identified the key features of the water chemistry,such as the extremely low levels of chloride,the near neutral pH,the relatively low cation content and the abundance of magnesium and calcium.The sum of the chemical characteristics and the surficial fumarolic activity indicate the presence of a shallow vapor-dominated zone,while the calcium and magnesium contents of the thermal waters suggest they are meteoric in origin.The surficial waters are thought to infiltrate to relatively shallow depths where they are heated by steam and volcanic gases rising through a vapor-dominated zone from a much deeper reservoir. Compositionally,the primary reservoir may be a hot sodium chloride brine overlying a cooling magma body.Silica geothermometry of the spring waters indicates that temperatures in the shallow perched reservoir may approach 150°C,while the large area covered by fumarolic and hot-spring activity suggests a hot geothermal system which may exceed 150°C (Motyka et al., 1981). A steep normal fault which trends N50W has been identified southeast of the thermal sites (Drewes et a/.,1961).The strike of this fault is directly in line with the thermal site,and could, Geothermal Development in Alaska 261 therefore,be acting as a conduit for heated fluids.Nakamura et a/.(1977)have determined that this N50W orientation is approximately the expected fracture direction,in light of the stresses generated by the subductive interaction of the Pacific and North American lithospheric plates presently occurring in the northern Pacific Ocean.Other fault and joint systems have been mapped in the area (Reeder,1981;Reeder,1982),and these also appear to be contributing to the hydrothermal convection process.Prominent near-vertical joints commonly trend N5SSW, N80W and N60E.The N60E orientation may be locally significant,for the thermal activity at Fields 2 and 3 appears to follow this direction.Furthermore,N40E-N60E is also the approximate trend of a line drawn between several igneous intrusions,and this may indicate that the contacts between the plutons and the Unalaska Formation are providing avenues for the circulation of heated fluids.Thus,the necessary conduits for the geothermal system appear to be the result of regional tectonics (subduction)and local plutonism.These processes are also important to the thermal activity in the vicinity of Makushin Valley. Makushin Valley has its source on the eastern flank of the volcano,and the valley trends west for roughly 13 km to its terminus at Broad Bay.The thermal sites are located in the upper reaches of Makushin Valley,a distance of about 20 km from Unalaska/Dutch Harbor. Hydrothermal activity in Makushin Valley is similar in many respects to that in Glacier Valley. For both areas,thermal manifestations consist of both hot springs and fumaroles.Also,the thermal waters are chemically similar;both locations are characterized by low chloride,high silica,high calcium and magnesium,and high bicarbonate and sulfate.Motyka ef a/.(1981) state that the comparatively high amounts of Ca and Mg,relative to the other cations,indicate that the waters are derived from the mixture of surface waters with deeper hotter fluids. Thermal springs in the area commonly occur at the base of the fumarole fields,and this suggests that at least part of the spring waters may originate as condensation of steam in surface waters.These meteoric waters then percolate into the substrata to finally discharge as springs. However,the high silica content of the thermal waters indicates that a large portion of the waters must have originated from a subsurface reservoir where temperatures exceed 150°C. But,since silica can equilibrate comparatively quickly (within several days to a few weeks),this suggests that the reservoir supplying the spring waters lies at a fairly shallow depth,and that this perched aquifer is heated by a much deeper reservoir (Motyka ef a/.,1981).The inferred deep reservoir is likely a high-temperature system,for three temperature gradient wells drilled during the summer of 1982 encountered maximum bottomhole temperatures of 200°C at a depth of 550 m in the plutonic rocks (Economides ef al/.,1982). In the summer of 1983 a new ''slim hole''well,ST-1,produced extremely encouraging results.At a depth of 1950 ft (594 m)it encountered hot water (T =366°F,186°C andp =508 psi,35.7 kg/cm').The well produced 50,000 [b/h (22.7 ton/h)through a slim pipe (diameter 77 mm).The wellhead conditions were:T =281°F,138°C,p =51 psi,3.6 kg/cm?and approximately 15%steam by mass. Recent workers (Kay ef a/.,1982)have stated that this portion of the Aleutian arc may be divided into four principal segments,as deduced from the geographic alignment of volcanoes and earthquake aftershock zones.Furthermore,the type of magmatic differentiation (calc- alkaline or tholeiitic)depends on the tectonic position of the volcanic centers with respect to the segment boundaries.If this hypothesis is correct,it could have important implications for the geothermal potential around Makushin Volcano.In the classification scheme of Kay ef al. (1982),tholeiitic magmas occur at segment boundaries and show characteristics consistent with low-pressure,high-temperature crystallization in large,shallow magma chambers;these characteristics include no hydrous phenocrysts,an iron enrichment trend on AFM diagrams, parallel REE patterns and vitrophyric lavas.In contrast,calc-alkaline magmas are generated within segments and display characteristics consistent with higher pressure and lower 262 M.J.Economides and G.N.Arce temperature crystallization.From the viewpoint of resource potential,tholeiitic magmas are desirable since they represent large,shallow,high-temperature energy sources.Since Makushin Volcano appears to display features of both calc-alkaline and tholeiitic sources,it is classified as '*mixed''in the initial report.However,chemical data from other studies (Drewes et a/.,1961; Perfit,1977;Arce,1983)indicate that Makushin Volcano is a tholeiitic edifice. Due to the attractiveness of Summer Bay (albeit marginal),there is no need to explore the direct heating potential of Makushin,especially since it is a prime target for power development (as previously discussed). Should a power plant be constructed to utilize the resource around Makushin Volcano,the plant would need to be close to the wells in order to minimize the loss in quality which accompanies steam transportation.Unfortunately,this necessitates a plant location danger- ously near an active volcano.At least 17 ''eruptions''have been reported since 1760,and seven of these appear to be actual volcanic eruptions.Based on these seven authentic events, Makushin erupts on average every 30 years.Since the last extrusive episode was in 1951,the volcano is statistically ready for another eruption.The most likely hazards to life and property in this vicinity would be from pyroclastic flows,mudflows,jokulhlaups and tephra fallout. Hazards associated with tsunamis,noxious gases,lightning and so on,would not be as serious. Therefore,any structures near the volcano should be built and maintained with these hazards in mind (Arce and Economides,1982). CONCLUSION While the engineering feasibility of geothermal development has been demonstrated,the economic feasibility is,as expected,tenuous. Geothermal Development in Alaska 263 Tenakee and Unalaska (Summer Bay)are the only sites that have even marginal attractiveness for direct utilization. For power generation physically hindered by the required quality of the geothermal fluid, there are two sites that may be attractive in the near and intermediate future:Unalaska (Makushin)and Copper Valley.The reduction in petroleum prices has a detrimental effect on geothermal prospects.Further,the minimum capacity requirements to make geothermal feasible would need either a consolidation of the present power users or an increase in the population or industrial base.In general,the present prospects of geothermal development in Alaska are bleak,with the possible exception of Unalaska.Therefore,capital outlays should be limited to resource identification via geological/geophysical surveys and perhaps limited exploratory drilling. REFERENCES Alaska Geological Consultants and Geonomics (1975)Technical feasibility of geothermal energy development,Drum thermal springs area,Alaska.Report to Geothermal Energy Program and Ahtna Regional Native Corporation. Andreasen,G.E.,Grantz,A.,Zeitz,1.and Barnes,D.F.(1964)Geologic interpretation of magnetic and gravity data in the Copper River Basin,Alaska.U.S.Geol.Surv.Prof.Paper 316-H. Arce,G.N.and Economides,M.J.(1982)Analysis of volcanic hazards from Makushin Volcano,Unalaska Island. Proc.1V N.Z.Geother.Workshop,pp.93-99. Arce,G.N.(1983)Volcanic hazards from Makushin Volcano,northern Unalaska Island,Alaska.M.S.thesis, University of Alaska,Fairbanks.: Beikman,H.M.(1980)Geologic map of Alaska.U.S.Geol.Surv.and Alaska Div.Geol.Geophys.Surv. Berg,H.C.,Jones,D.L.and Coney,P.J.(1978)Pre-Cenozoic tectonostratigraphic terranes of southeastern Alaska and adjacent areas.U.S.Geol.Surv.Open-File Report 78-1085. Brew,D.A.and Morrell,R.P.(1980)Intrusive rocks and plutonic belts of southeastern Alaska,U.S.A.U.S.Geol. Surv.Open-File Report 80-78,pp.|-34. Dames and Moore (1980)Geothermal drilling studies near Unalaska,Alaska.Report to Alaska Div.of Energy and Power Development. Drewes,H.,Fraser,G.D.,Snyder,G.L.and Barnett,H.F.Jr.(1961)Geology of Unalaska Island and adjacent insular shelf,Aleutian Islands,Alaska.U.S.Geol.Surv.Bull,1028-S,583-676. Economides,M.J.,Ansari,J.,Arce,G.N.and Reeder,J.W.(1982)Engineering and geological analyses of the geothermal energy potential of selected sites in the state of Alaska.Proc.VIII Workshop Geother.Reservoir Engng, Stanford University. Economides,M.J.,Reeder,J.W.and Markle,D.(1981)Unalaska geothermal development.Proc.N.Z.Geother. Workshop,pp.7-12. Hudson,T.(1977)Geologic map of Seward Peninsula,Alaska.U.S.Geol.Surv.Open-File Report 77-796A. Jones,D.L.,Siberling,N.J.,Berg,H.C.and Plafker,G.(1981)Map showing tectonostratigraphic terranes of Alaska,columnar sections,and summary description of terranes.U.S.Geol.Surv.Open-File Report 81-792. Kay,S.M.,Kay,R.W.and Citron,G.P.(1982)Tectonic controls on tholeiiti¢and calc-alkaline magmatism in the Aleutian arc.J.geophys.Res.87,4051 -4072. Kern,D.Q.(1950)Process Heat Transfer.McGraw-Hill,New York. Lankford,S.M.and Hill,J.M.(1979)Stratigraphy and depositional environment of the Dutch Harbor Member of the Unalaska Formation,Unalaska Island,Alaska.U.S.Geol.Surv.Bull.1457-B. Marsh,B.D.(1982)The Aleutians.In Andesites (Edited by Thorpe),pp.99-114.Wiley. Miller,D.S.(1981)Tenakee drilling project.Report to Alaska Div.of Power and Energy Development. Motyka,R.J..Moorman,M.A.and Liss,S.A.(1981)Assessment of thermal springs sites in the Aleutian arc,Atka Island to Becherof Lake-preliminary results and evaluation.Alaska Div.Geol.Geophys.Surv.Open-File Report 144,pp.68 -89. Nakamura,K.,Jacob,K.H.and Davies,J.N.(1977)Volcanoes as possible indicators of tectonic stress orientation- Aleutians and Alaska.Geofis.pura appl.115,87-112.Nichols,D.R.and Yehle,L.A.(1961)Mud volcanoes in the Copper River Basin,Alaska.Proc.Ist Int.Symp.Arctic Geology,Calgary,Vol.2,pp.1063-1087.- Nye,C.J.(1982)The Wrangell Volcanoes-voluminous volcanism accompanying microplate accretion.Geol.Soc. America Cordilleran meeting,Anaheim,California,Vol.14,p.221.,Peters,M.S.and Timmerhaus,K.D.(1980)Plant Design and Economicsfor Chemical Engineers (3rd edn.).McGraw- Hill,New York. Perfit,M.R.(1977)The petrochemistry of igneous rocks from the Cayman Trench and the Captains Bay pluton, Unalaska Island.Their relations to tectonic processes at plate margins.Ph.D.dissertation,Columbia University. Reeder,J.W.,Coonrad,P.L.,Braggs,N.J.,Denig-Chakroff,D.and Markle,D.R.(1980)Alaska geothermal implementation plan.Draft to Alaska Dept.of Natural Resources and U.S.Dept.of Energy. Reeder,J.W.(1981)Vapor-dominated hydrothermal manifestations on Unalaska Island,and their geologic and tectonic setting.4 CEI Svmp.Arc Volcanism,pp.297 -298. 264 M.J.Economides and G.N.Arce Reeder,J.W.(1982)Hydrothermal resources on the northern part of Unalaska Island,Alaska.Alaska Div.Geol. Geophys.Surv.Open-File Report 163. Turner,D.L.and Forbes,R.B.(1980)A geological and geophysical study of the geothermal energy potential of Pilgrim Springs,Alaska.University of Alaska Geophysical Institute Report UAG R-271. Turner,D.L.and Swanson,S.E.(1981)Continental rifting-a new tectonic model for the central Seward Peninsula. In Geothermal Reconnaissance Survey of The Central Seward Peninsula,Alaska (Edited by Wescott,E.M.and Turner,D.L.).University of Alaska Geophysical Institute Report UAG R-284. Waring,G.A.(1917)Mineral springs in Alaska.U.S.Geol.Surv.Water Supply Paper 418. Wescott,E.M.and Turner,D.L.(1982)Geothermal energy resource assessment of parts of Alaska.Report to the Div.of Geothermal Energy,D.O.E. 7,ere SF.07.OF EVAULATION OF THE MAKUSHIN GEOTHERMAL RESERVOIR, UNALASKA ISLAND Michael J.Economides(1),Charles W.Morris(2),and Don A.Campdei1'3) 1.Untversity of Alaska,Fairbanks,AKNowwithDowell-Schlumberger,London 2.Republic Geothermal,Inc.,Santa Fe Springs,CA Now with Schlumberger Offshore Services,New Orleans,LA 3.Republic Geothermal,[nc.,Santa Fe Springs,CA ABSTRACT Analysis of an extended flow test of well ST-1 on the flanks of Makushin Volcano indicates an extensive,water-dominated, Naturally fractured reservoir.The reser- voir appears ta be capable of delivering extremely large flows when tapped by full- size preduction wells.A productivity index in excess of 30,000 Ib/hr/psi implies a phenomenal permeability-thickness product,in the range of 500,000 to 1,000,000 ad-ft.° The flowing bottomhole (1,949-foat) temperature of the Fluid ts 379°F,which Is lower than the measured static temperature at that depth (395°F).This phenomenon, coupled with an observed static temperature gradient reversal from the maximum 399°F observed at 3,500 feet,indicates that the reservoir proper {ts located some distance from the well.Presumably it fs at a temperature slightly lower than 379°F and communicates with the wellbore via a high conductivity fracture systes. A material balance calculation yields an estimate of reserves that are capable of sustaining all of the present power needsofthe{sland (13+MW peak)with ageothermalpowerplantforseveralhundredyears.Theoretically,a single largediameterwellatthesiteofST-1 could satisfy this requirement. NTRO ON Unalaska Island,located in the central portion of the Aleutian Chain has been the site of a.msltt-year exploration programfortheevaluationofitsgeothermalenergypotential(Figure 1).Makushin Volcano, the 6,680-foot high active volcano, situated on the northern end of the island, has a large number of surface manifesta- rons.including several large fumarolefields. PROJECT LOCATION MAP Following extensive geological,geo- physical,and geochemical surveys of the Makushin region,three +1,500-foot tempera-ture gradtent holes were sited and drilled in the summer of 1982.The hales and thetr temperature gradients were described by Isselhardt,et al (1983a),who also provided 2a geothermal resource mode)of the Makushin geothermal area (Isselhardt,et al,19836). The heat 'source of the Makushin geo-thermal system appears to be a buried igneous.intrusion associated with the volcano.The temperature and post-glacial volcanic distributions suggest that the heat source for the system is not directly beneath the sumait,but rather ts offset to the east.The location of the Makushin producing horizon,a fractured diorite, appears to be structurally controlled by 4 major northeasterly striking fracture zone. In the summer of 1983,a stratigraphic test well (ST-1)was drilled near one of the 1982 temperature gradient holes (£-1). A steam zone was encountered at 672 feet, followed by a significant §fracture at1,946 feet,where the drillistem dropped free for three feet. The 1983 well testing desertbed byCampbellandEconomtdes(1983)confirmed a highly prolific reservoir producing47,000 lb/hr through three-inch pipe with little or no detectable pressure drawdown.Inadequately sensitive Amerada-type pres-sure instrumentation prevented rigorous.analysis.<A productivity index of over3,000 Ib/hr/psi and a permeability thick. fess of over 50,000 md-ft were inferred.A Tong flow test in the susmer of 1984 was intended to provide a better estimate of these reservoir parameters as well as demonstrate sustained flow capability. ST FACY S_ANO INSTRUMENTATION The surface equipment utilized duringthe1984testingwasbasicallythesameasthatusedtn1983anddescribedinthe report by Campbell and Economides (1983).Figure 2 shows the surface equipmentarrangementsutilizedduringthelong-termtestof1984.A relatively simple two- MAKUSHINWELLTESTEQUIPMENT phase ortfice meter and James tube were installed at the end of the flow line to measure the flow rate.Upstream and down- stream orifice pressures were recorded Simultaneously with a differential pressure flow meter.The James tube lip pressure was monitored continuously during the flow test utilizing both a test quality pressure gauge and 2 Barton pressure recording meter.In addition,the wellhead pressure and temperature were recorded continuously on Barton meters throughout the flow test.The ortfice plate described above wasutilizedtoacalculate:the enthalpy of the flutd using the "empirical equation developed by Russel James (1980). Qewnhole pressure and temperaturemeasurementswere"obtatned using two separate monitoring systems.The pressure monitoring equipment was a capillary tubesystemwhichuttlizedagasfilled,volu- metric chamber downhole connected to a very small dtameter captilary tube with 2 sur- face recording pressure transducer.This equipment was filled with helium gas as the pressure transmitting saedium from the bottomhole to the surface transducer.The equipment utilized itn this test has an accuracy of approximately +0.3 pst,with a sensitivity of +0.1 psi on the transducer.The temperature measurements were obtained using a thermocouple cable systemcompletelyseparatefromthecapillary tube.This required that the temperature data and the pressure data be acquired tn separate runs in the well.The thermo- couple was a cChromel-alumel,groundedjunctton-type with an accuracy of +»3degreesFandasensitivityof+3/4 of a degree F.The thermocouple cable and the capillary tube were contained on two separate spools.As will be seen in the data discussed later,the pressure data and the temperature data were found to be quite feproducible throughout the flow test (unlike the prior years'data with Amerada- type instrumentation). FLOW TEST MEASUREMENTS The test of ST-1 consisted of two flow periods of approximately 33,000 lb/hr and 63,000 lb/hr each.'The test rate/wellhead pressure/bottomhole pressure history is shown in Figure 3.The first Flow period eh} marten Gt=t Low TERT 1 a -.Cd ory pono iL.SE eereremesah -I"T =e - .o a - »Jae a on,Pee.poe?jTmene<n anve -itewfso we UT ene wom ,ane: - s **.a a a a o fone lasted 15 days,whtle the second flow pertod at the higher rate lasted 19 days.Ourtng the 34 days of flow from ST-1,therewereseveralminorchangestntheflowrate and/or a bypass of the measuring system in order to perform sampling experiments or to modify the flow equipment.However,thetestproceededrelativelysmoothly,with the two flow rates being maintained at essentially constant conditions throughout their respective test pertods. Petor to the initiation of flow from ST-1,a static temperature profile of thewellborewasobtainedonJuly3andastaticpressureprofilewasobtainedon July 4,as shown in Figure 4.Thesesurveysclearlyindicatethatthewellhas a steam zone,with the vapor-liquid inter- face located at about 825 feet.This Is shown by the constant temperature and pres- sure conditions extsting in the upper part eeONiryof the wellbore until very near the surface(#200 feet).Below 6825 feet there 1s aliquidzonewhichincreasestoasaxinus temperature of 399°F at the 1,500-foot depth,then shows a slight decline ta a temperature of 395°F at the bottom of the wellbore (1,949 feet}. FIGURE4STATICTEMPERATURE(JULY 3,1984) ANQ PRESSURE (JULY4,1964)IN ST=4 rereunst comms * @ 30 100 10 m0 BOS DOO me ceo ee see me one me [ = os : oo 2 LEN \.i N \._ANU _ -N -TNwweLf N see wee Ul)N ee After flow was initiated onJuly5,1984,the well stabilized at a flow rate of about 33,000 lb/hr and this cond{- tion was maintained unti!July 20,1984. During this flow period the pressure tool was left at the bdottom of the well (1,949 feet),continuous ly recordingbottomhalepressure,except for the times when wellbore pressure and temperature profiles were obtained.Flowing pressure and temperature proftles were obtained onduly6.The results are shows in Figure §.A second set of pressure/ temperature profiles were obtained on July 19,which were exact overlays of theJuly6profiles.About one psi of drawdown was observed over the 15 days at the low rate.: Following the change in the flow to the higher.rate of 63,000 Ib/hr on July 20-21, another pressure/temperature profile was obtained (Figure 6).On August 7,1984,afinal.pressure profile was obtained which was.again an exact overlay of the July 23 profile.Ouring the high-rate flow period, the pressure tool was again left at the bottom of the hole continuously recording bottomtole pressure except when profiles were run.An additional one pst of draw- FIGURE 5 FLOWING TEMPERATURE (JULY 6 1964) ANO PRESSURE (JULY 6,1984)IN ST 1 Teewanag oer mai --L SOREL . :_\ 1008 i 1988 1308 see NS 1-0 oe N 1008 i IN _ --UNOO seve eo mm 0s 1s we me HO WO 8 8 NS we Oe down was observed during the 19-day high rate period.The well was shut-in on August 8,1964,with the pressure tool hanging in the well at bottom.The pres- sure tool recorded butidup data for the next 17 days,snowing less than one pst of increase in bottomhole pressure. FIGURE68FLOWINGTEMPERATURE(JULY20,1964)ANQ PRESSURE (JULY21,1984)IN ST-¢ Teowung cures 7 ©20 wee we 250 Be we m0 00 se tO SUE Oe EEK \. -\.nk _ i.-a NUT _ -N _i K _.meee I Cc HEN ee OISCUSSION AND INTERPRETATION OF RESULTS Although the resolution of the pressure equipment during thts test was far superior to that used during the 1983 test program, 1t was again found that the drawdown pressure response in ST-1 was extremely small,perhaps beyond the true sensitivity of the tnstrumentation.It appears that the pressure drawdown during the low-rate flow period was on the order of one pst, while the pressure drawdown in ST-3 during the high-flow rate was on the order of two pst.Thus,the productivity index derived from the two flow periods equals 317,000-33,000 Ib/hr/psi.These values are very large (an order of magnitude more than the ones postulated in 1983),and Indicate that the productivity of the Makushin reservoir is extremely high.Precise calculation of the permeabtlity-thickness product {$s not possible with these data, although it ts easy to infer that the value 1s phenomenally large ({.e.,500,000 to 1,000,000 md-ft}. Produced flutd enters the wellbore at the bottom of the well,1,946-1,949 feet, at a temperature of 379°F,which is less than the static temperature tn the wellbore at that level (395°F).This indicates that colder water is entering the well from some other area of the reservoir,probablyshallower,along an unknown fracture path. After shut-in,the wellbore re-equilibrates | to {ts static condition.Thus,the fluid density within much of the wellbore column lightens over a period of time as it returns to a higher static temperature. Because there is essentially only one taflow point,however,and pressure buildup was measured opposite this point,the re-equilibration of the wellbore fluid density should have no effect on the accuracy of the measured reservatr pres- sure.Therefore,the lack of full pressure recovery (only one psi rather than two)is not explained by thermal equilibration,but rather may be attributable to a real decrease in average reservoir pressure. Well Potential The estimation of individual well power potenttal for commercial operations requires the fundamental assumption that an extensive reservoir can be represented by the fluid properttes,initial pressure, temperature,and productivity index derived from slim hale data such as that froa ST-1.Glven this as a basis,a wellbore flow model ytelding wellhead pressure vs rate must First be validated against the measured slim hale conditions.Once a match is achieved,then wellhead pressure vs rate curves for various commerctal-size wellbore.configurations may be generatedandretatedtoappropriatepowercycles with some degree of confidence. The flow simulator used for this study was developed by Intercomp (1982)and has been used extensively by the industry for geothermal and geopressured wellbore flow calculations for several years.It ts a vertical,multiphase flow simulator which Incorporates treatment for vartable wel) diameter with depth,heat losses,and noncondensable gases.The *nomtnal®commercial well condttions arrived at were as follows: Initial Pressure we 494 psig at 1,949 feet Inflow Temperature =379°F at 1,949 feet Salinity =4,000 ppm TOS C02 Content =200 pope Productivity Index «31,500 Ib/hr/ps}13-3/8 or 16 Inch Wellbore Ustng these conditions,simulator- generated curves for wellhead pressure vs flow rate were constructed for the two different "commercial®wellbore sizes(Figure 7).At a reasonably optimum wellhead pressure of 60 psia (for power generation from this resource),a flow rate of 1,250,000 to 2,000,000 Ib/hr is predicted,depending on wellbore size. ween MAICLSHEECOMMERCIA,SIZE WELL PRENCTED FLOW RATE ve,WELAHEAD PRESSE [.7Reserve Estimation Using a Matertal Balance Calculation Material balance caleutattons forlargelyincompressiblesystems,such as the one at the Makushin geothermal reservoir, have been developed and used by 4 number of Investigators itn the petroleum literature.The intttating step is an =expresstonprovidingthe!sothermal compressibility. ce-]av (1)¥apT Assuming that the total compressibility ofthesystemsisconstant,Equation1 may beintegrated: V2 =ec4p (2) y and because the recovery tn terms of reservoir volumes is defined as: fa V2-¥y ,(3) Lal then a combination of Equations 2 and 3resultstas V9-¥2 eho 2}1 The cumulative production in terms of reservoir volumes is,of course,Vo-Vyand,because the fluid ts considered incompressible,the ratic Yo-¥y (4)y may be taken as: Hp C) whtch ¥s the ratio of the cumulative amass produced to the initial sass-tn-place. Hence,Equation 4 becomes: Wp =e(CAp)1 (5) w °° Of the variables tn Equation 5,Wy1stheoneknownwithcertainty.In this case Wy 1s equal to: Wy =33,000 x 15 x 26 »63,000 x 19x24=4.06 x 107 Ibs reflecting the two flow periods. The vartables contained in the exponential expression consist of the total compressibility of the system and the average reservoir pressure drop observed during the flow pertod.In this system, the total compressibility ts the sum of the individual rock and fluid compressibilities. Ce =Cy Ce (6} Water compressibility ts normally taken as3x10-6 pst-1,while the 'compresst- bility of the rock could reasonably rangebetween2x10-6 psi-!and 6 x 10-5 pst-i, depending on the lithology and the elasti- city of the geologic features.for most reservoirs the value of the compressibility{s taken as equal to 6 x 10-8 pst-l,This value will be used here with =the knowledge that it could be somewhat higher or lower. The total observed bottomhole pressure drop at ST-1 during the 34 days of the flow test was less than two psi.The subsequent pressure buildup test resulted in less than one psi pressure gain.Both tests indicate an extremely large permeability-thickness product which {s conststent with the small pressure differences observed.The total average reservoir pressure drop !s assumed to be roughly one psi. Using Equation 5,the iInitial- fluid-in-place may then be calculated: 4.06 x 107e (6x 10-8 x1)1 y r yielding W =6.8 x 1012 ibs.Given the uncertainties inherent In this calculation,the value of "W*can be considered order of magnitude only. Nonetheless,assuming a single full- size production well drilled on the site of ST-1 ytelding 1,500,000 lb/hr (depending on the power cycle used it could generate 7-32 MWe),the longevity of this reservoir is extremely large relative to the needs of Unalaska Island (currently only about 13 MM peak).The calculated initial-mass-in- place could deliver this flow rate for over 500 years.: CONCLUSIONS Results from the slim hale ST-1 flow test tm 1984 confirmed the basic Makushin model of a shallow steam zone overlying a ltquid-dominated reservoir in fractureddiorite.A flowing temperature at"1,949 feet was found to be 379°F.This fluid appears to be entering the wellbore along a fracture which brings in colder water than would be expected by the 395°F static temperature of the fracture zone. The flow testing of the well in 1984 proved that the reservaitr is potentially highly productive,even with only three feet of fracture interval open to the wellbore. Sustained flow through a three-inch dta - meter wellbore of 63,000 lb/hr was achieved with Tess than two psi of pressure drawdown from the initial pressure of 494 psi.This suggests a very large permeabtlity-thickness value for the reservoir.The well productivity index obtained duringthistestwasapproximately30,000 Tb/hr/pst.Wellbore flow modelingindicatesthatcommerical-size wells should be capable of one to two million Ib/he rates.A material balance calculation indicates a theoretical electricity reservesufficientfortheneedsofthetslandfor several hundred years at current consuap- tion rates.In general,the data obtained during the 1984 Flow test is consistent with the results obtained during the short- term flow test of 1983,and confirms the existence of a substantial resource. 2. 3. REFERENCES Issethardt,C.F.,et a7 (1983a), "Temperature Gradient Hole Results from Makushin Geothermal Area,Unalaska Island,Alaska,*Geothermal Resources Counct]Transactions,Vol.7,Setober 1983,pgs.95-98. Tsselhardt,C.F.,et al (1983b) "Geothermal Resource Model for the Makushin Geothermal Area,Unalaska Island,Alaska,"Geothermal Resources Counet!]Transactions,Vol.7,October 1983,pgs.99-102. Campbell,0.A.,and Economides,M.J. (1983),'A Sumaary of Geothermal Exploration and Data from Stratigraphic Test Well No.1,Makushin Volcano, Unalaska Island,*Proceedings of the Ninth Workshop on Geothermal ReservoirEngineering,Stanford University,December 1983,pgs 167-174. James,Russell (1980),'A Choke-Meter for Geothermal Wells.Which Measures Both Enthalpy and Flow,®Geothermal Energy,May 1980,pgs.27-30.- "Vertical Steam-Water Flow in WellswithHeatTransfer,”SctentificSoftware-Intercomp,February 1982. ACKNOWLEDGEMENTS The authors wish to thank the Alaska Power Authority for their suppert and numerous memebers of Republic's staff for their input to thts report. "3 - ALASKA POWER AUTHORITY 334 WEST 5th AVENUE -ANCHORAGE,ALASKA 99501 Phone:(907)277-7641 (907)276-0001 September 22,1983 PRESS RELEASE CONTACT Don Markle Patti DeJong On August 25,the Makushin State #1 geothermal well encountered a substantial geothermal hot water resource on Unalaska Island 800 miles southwest of Anchorage.The geothermalexplorationwellwasdrilledbyRepublicgeothermal,Inc.of Santa Fe Springs,California,and Arctic Resource Drilling Company of Anchorage,Alaska,for the Alaska Power Authority. The drilling crew encountered a three foot fracture void in the diorite Unalaska rock formation at 1,947 feet.The weil subsequently flowed an artesian mixture of hot water and 16 percent steam with a bottom hole temperature of 370°F.The bottom hole pressure was recorded at 471 psig. State officials are optimistic about the commercial prospects of this resource discovery on the slopes of Makushin Volcano 12 miles north of the Port of Unalaska.Governor Sheffield,who has consistently endorsed the economic development of the State's geothermal resources,said "I am quite pleased that the breakthrough in the development of this steam resource has occurred early in my administration.I have instructed Commissioner Dick Lyon,of the Department of Commerce &Economic Development,and Eric Yould,of the Alaska Power Authority to move forward to fully assess the economics of power generation at Unalaska and to find private sector partners for the State to assist in financing and developing the resource." The discovery of the geothermal reservoir is a result of a three year exploration program funded through a $5,000,0C0 State appropriation to the Power Authority.Prior to this appropriation, preliminary economic and resource evaluation of Unalaska's geothermal potential was completed in combined studies by the State Geological and Geophysical Survey,University of Alaska Geophysical Institute,Oregon Institute of Technology Geo-heat Center and United States Department of Energy. "A good deal of the credit for helping get this project under way goes to former ex-Unalaska Representative Eric Sutcliffe and Dr.John Reeder of the State Geological Survey"says Alaska Power Authority Project Manager Don Markle,"They did a lot of the criginal work in calling attention to ihe project potential, including Dr.Reeder's discovery of a strategic fumerole field and assistance in estabiisting the site eventually drilled."7 -'Proyy Code:oe File Code:UF.OS Vi! 234/053 J.Date PS 2US->j Eric Sutcliffe and Senator Mulcahy of Kodiak were the sponsors of the appropriation. The 1981-1982 exploration effort included geological and tepographic mapping,chemical analysis,core sampling,mercury sampling,gravity survey,air photo analysis,self potential Surveys and environmental work in a joint effort by Republic Geothermal and the State Geological and Geophysical survey.Three temperature gradient wells were drilled in 1982 by Republic Geothermal and Exploration Supply and Equipment Company of Anchorage.The maximum temperature in the gradient wells was in excess of 390°F.The interpretations of field data by Republic Geothermal and the State Geological survey indicated the potential for a geothermal reservoir system within 4,000 feet of the surface. "The geological and drilling results were encouraging enough for the Power Authority to attempt confirmation of the resource predicted at Makushin."Said Markie,"We initiated drilling operations the middle of June and completed demobilizaticn the 19th of September.Between these dates we had to abandon one well because of a lost tool down the well,a helicopter was lost,and we discovered the largest geothermal resource with potential for economic power development in Alaska." "The resource is very impressive,"says Professor of Petroleum Reservoir Engineering,Michael Economides of the University of Alaska,Fairbanks;consultant to the Power Authority."The reservoir analysis conducted by Don Cambell (Republic's ReservoirEngineer)and myself indicate the formation permeability thickness of the reservoir is very large.We are unable to calculate the extent ot the reservoir without a long duration flcw test,which indicates the system is very large.The present 2 3/4"test well flows 53,000 pounds of steam and hot water an hour which could produce 500 kilowatts of electricity,explained Professor Economides who has participated in the project since its inception. Production sized wells could be expected to produce approximately 2 MW power each. The future of the project depends on economics according to Patti DeJong,Director of Project Evaluation for the Power Authority."We are presently assessing the potential of geothermal genereted electricity versus other alternatives such as wind, diesel and hydroelectricity available to Unalaska."The economic study will be completed in November and is being done by the Anchorage office of Acres American,Inc.This independent evalu- ation is called a "reconaissance study"and is required by the Power Authority prior to any future work."If we have positive results from the reconaissance study,the Power Authority can initiate a more detaiied feasibility analysis of geothermal power development,"saia DeJong.DeJong explained that "Lend status in 224/053 the area is compiicated and wey impact development of the geothermal resources."The land has been selected by the Aieut Corpcration under a provision of the Aleska Native Claims Settlement Act,Fut must be reconfirmed and trens'ferrea by the federal government."Development cannot proceed until the transfer,"says DeJong.In the event land transfer never takes place,the land will revert back to the Aleutian Wildlife Refuge according to DeJong. The city of Unalaska is beginning consolidation of the locai power generation into a unified power system."The power demand is very impertant to development of a geothermal power plant and the consolidation of the many pever generation facilities into a single grid is a very positive step,"says Markle."The ability to negotiate a power sales agreement with one utility will be much more acceptable than negotiations with thirteen independerts," explains Markle.The upgrading of the existing transmission lines is also necessary to supply the power to ali tre homes."Projecteconomicswillrecuireasizeablemarketforthepcewertobecroduced.Consolidation of the grid in Unalaska will result in approximately a 10 MW demand. The cost per kilowatt hour is normally less for a large 50MW development than small 10MW development due to the basic costs of design and access on gestherma?projects."When we first considered the development we felt a 30 MW load would be necessary to compete in cost per kilowatt hour with a consolidated diesel system.The fact that we have a shallow cecthermal system along with the possibiiity cf development at the more accessible Sugarlcaf area near the means costs for geothermal may prove to be much less,and that the breakeven demand point will be reduced," said Markle.Decong pointed out that power reovirement predictions range from 20 -40 MW for the year 2000."The cevelopment of the resource would take approximately seven years assuming questions of land status,financing and licensing are resolved,"says Cedcng. The resource appears large enough to sustain not only initial predictions of load growth for Unalaska,but perhaps even for new industrial ccnsumers,"says Markle."One advantage of geothermal resources,aS opposed to hydroelectric,is that they can be developed incrementally as demand grows.Normally the additional capacity is cheaper to install per kilowatt as well,"says Markle. "The present 34¢per kilowatt hour cost for electricity is the cost of electricity with which the project must compete.Power Authority officials appear optimistic that the project will be competitive. The 1984 field program for the Makusnin geotherrial project will consist of a 3 to 5 month flow test,and the drilling of a temperature gradient well in the more accessiole Sucarloaf area.The intent cf the program is to determine the size of the reservoir and whether it can be produced at a more acces-izie sive. 234/053 Additional analysis that may be conducted in 1984 includes additional geophysical studies to help determine reservoir boundaries and drilling deeper in the discovery well to locate predicted higher temperature and pressure fluids.Representative Adelheid Herrmann travelled to Unalaska with several other Representatives to view the discovery and to assess the prospects for development of the reservoir during the week of September 19. 234/053 7.03 September 21,1983 PRESS RELEASE CONTACT Don Markle Patti DeJong On August 25,the Makushin State #1 geothermal well encountered a substantial geothermal hot water resource on Unalaska Island 800 miles southwest of Anchorage.The geothermal exploration well was drilled by Republic geothermal,Inc.of Santa Fe Springs,California,and Arctic Resource Drilling Company of Anchorage,Alaska,for the Alaska Power Authority. The drilling crew encountered a three foot fracture void in the diorite Unalaska rock formation at 1,947 feet.The well subsequently flowed an artesian mixture of hot water and 16 percent steam with a bottom hole temperature of 370°F.The bottom hole pressure was recorded at 471 psig.ot heyffoPWe State officials are optimistic about the commercial prospects of this resource discovery on the slopes of Makushin Volcano 12 miles north of the Port of Unalaska.Governor Sheffield,who has consistently endorsed the economic development of the State's geothermal resources,said "I am quite pleased that the breakthrough in the development of this steam resource has occurred early in my administration.I have instructed Commissioner Dick Lyon,of the Department of Commerce &Economic Development,andEricYould,of the Alaska.Power Authority to move forward to fullyassesstheeconomicsofpowergenerationatUnalaskaandtofind private sector partners for the State to assist in financing and developing the resource." The discovery of the geothermal reservoir is a result of athreeyearexplorationprogramfundedthrougha$5,000,000 StateappropriationtothePowerAuthority.Prior to this appropriation, preliminary economic and resource evaluation of Unalaska's geothermal potential was completed in combined studies by the State Geological and Geophysical Survey,University of Alaska GeophysicalInstitute,Oregon Institute of Technology Geo-h Center andUnitedStatesDepartmentofEnergy.Heolje"A good deal of the credit for helping get this project underY_fay goes_to former ex-Unalaska Representative Eric Sutcliffe andre.John Ryder of the State Geological Survey"says Alaska PowerAuthorityProjectManagerDonMarkle,"They did a lot of the original work in calling attention to the project potential,including Dr.Reeder's discovery of a strategic fumerole field andassistanceinestablishingthesiteeventuallydrilled." Proj.Code:cv acoFileCode:2-7 g3 Vl234/053/J.Date:Y¥3-a4 t oatve Eric Sutcliffe and Senator Mulcahy were the sponsors of the appropriation. The 1981-1982 exploration effort included geological and topographic mapping,chemical analysis,core sampling,mercury sampling,gravity survey,air photo analysis,self potential surveys and environmental work in a joint effort by Republic Geothermal and the State Geological and Geophysical survey.Three temperature gradient wells were drilled in 1982 by Republic Geothermal and Exploration Supply and Equipment Company of Anchorage.The maximum temperature in the gradient wells was in excess of 390°F.The interpretations of field data by Republic Geothermal and the State Geological survey indicated the potential for a geothermal reservoir system within 4,000 feet of the surface. "The geological and drilling results were encouraging enough for the Power Authority to attempt confirmation of the resource predicted at Makushin."Said Markle,"We initiated drilling operations the middle of June and completed demobilization the 19th of September.Between these dates we had to abandon one well because of a lost tcol down the well,a helicopter was lost,andwa<& discovered the largest geothermal resource with potential for economic power development in Alaska." "The resource is very impressive,"says Professor of Petroleum Reservoir Engineering,Michael Economides of the University of "S$Alaska,Fairbanks;consultant to the Power Authority."The phick reservoir analysis conducted by Don Cambell (Republic's ReservoiEngineer)and myself indicate the formation permeability "of the reservoir is very large.We are unable to calculate the extent of the reservoir without a long duration flow test,which indicatesthesystemisverylarge.The present 2 3/4"test well flows 53,000 pounds of steam and hot water an hour which could produce 500 kilowatts of electricity,explained -@m™Economides who has participated in the project since its incgption.Production sized wells could be expected to produce approxjmately 2MW power each.C.t§§ohThefutureoftheprojectdependsoneconomicsaccording to Patti DeJong,Director of Project Evaluation for the PowerAuthority."We are presently assessing the potential of geothermal generated electricity versus other alternatives such as wind, diesel and hydroelectricity available to Unalaska."The economic study will be completed in November and is being done by theAnchorageofficeofAcresAmerican,Inc.This independent evalu-ation is called a "reconaissance study"and is required by the Power Authority prior to any future work."If we have positive results from the reconaissance study,the Power Authority can initiate a more detailed feasibility analysis of geothermal powerdevelopment,"said DeJong.DeJong explained that "Land status intheareaiscomplicatedandmayimpactdevelopmentofthegeothermalresources."The land has been selected by the Aleut 234/053 Corporation under a provision of the Alaska Native Claims Settlement Act,but must be reconfirmed and transferred by the federal government."Development cannot proceed until the transfer,"says DeJong.In the event land transfer never takes place,the land will revert back to the Aleutian Wildlife Refuge according to DeJong. The city of Unalaska is beginning consolidation of the local power generation into a unified power system."The power demand is very important to development of a geothermal power plant and the consolidation of the many power generation facilities into a single grid is a very positive step,"says Markle."The ability to negotiate a power sales agreement with one utility will be much more acceptable than negotiations with thirteen independents," explains Markle.The upgrading of the existing transmission lines is also necessary to supply the power to all the homes."Project economics will require a sizeable market for the power to be produced.Consolidation of the grid in Unalaska will result in approximately a 10 MW demand. The cost per kilowatt hour is normally less for a large 50MW development than small 1OMW development due to the basic costs of design and access on geothermal projects."When we first considered the development we felt a 30 MW load would be necessary to compete in cost per kilowatt hour with a consolidated diesel system.The fact that we have a shallow geothermal system along with the possibility of development at the more accessible Sugarloaf area near the means costs for geothermal may prove to bemuchless,and that the breakeven demand point will be reduced," said Markle.DeJong pointed out that power requirement predictions range from 20 -40 MW for the year 2000."The development of the resource would take approximately seven years assuming questions of land status,financing and licensing are resolved,"says DeJong. The resource appears large enough to sustain not only initial predictions of load growth for Unalaska,but perhaps even for new industrial consumers,"says Markle."One advantage of geothermal resources,as opposed to hydroelectric,is that they can bedevelopedincrementallyasdemandgrows.Normally the additional capacity is cheaper to install per kilowatt as well,"says Markle. "The present 34¢per kilowatt hour cost for electricity is the cost of electricity with which the project must compete.PowerAuthorityofficialsappearoptimisticthattheprojectwill be competitive. The 1984 field program for the Makushin geothermal project will consist of a 3 to 5 month flow test,and the drilling of a temperature gradient well in the more accessible Sugarloaf area. The intent of the program is to determine the size of the reservoir and whether it can be produced at a more accessible site. Additional analysis that may be conducted in 1984 includes additional geophysical studies to help determine reservoir 234/053 boundaries and drilling deeper in the discovery well to locate predicted higher temperature and pressure fluids.Representative Adelheid Herrmann travelled to Unalaska with several other Representatives to view the discovery and to assess the prospects for development of the reservoir during the week of September 19. 234/053 ).O8 3 FiBiggeothermalenergysitediscovered By ANN CONY 'a fee Daily News business reporter /3 v3 A huge reservoir of geothermal energy boils under a volcano near Dutch Har- bor,but the remoteness of the site may prevent it from becoming a major source of electrical generation. The discovery of the geothermal site at Makushin Volcano on Unalaska Island 'was announced by the state. "It's one of the most significant finds _in the world,''said Don Markle,project manager for the Alaska Power Authori- ty. Markle said the Makushin discoveryofsteamenergyiscomparable,in energy terms,to that of an oil field larger than the 1.3-billion-barrel Kuparuk River field on Alaska's North Slope. If the discovery had been made near Anchorage,Fairbanks or any major pop- ulation center,its significance would be unquestioned.But electricity generated from geothermal energy must be used near its source,and whether it will be economical to develop the volcano's steam to drive power turbines for Dutch Harbor and the neighboring town of Unalaska is not yet certain. Gov.Bill Sheffield said in a prepared statement that he has directed the power authority and the state Department of Commerce and Economic Development to evaluate the volcano's development po- tential and "'to find private sector part- ners for the state to assist in financing and developing the resource.”' Patti DeJong,director of project eval- uation for the power authority,said. Republic Geothermal Inc.,a California company and the prime contractor for exploration of Makushin's geothermalpotential,has shown some interest in a partnership.''They have been known to take equity positions,”she said. If development is judged economical, Dutch Harbor seafood processors,who have voracious appetites for electricity, might also be interested in joining the project,according to DeJong. Exploratory drilling at the volcano in the summer of 1982 found steam at temperatures of 365 degrees Fahrenheit 1,947 feet below the surface,Markle said. Recent drilling revealed a fractured rock system that could serve as the conduit from the underground steam reservoir to the earth's surface. The precise size of the steam reservoir is still being calculated,but pressure tests indicate it is among the largest in the world,and the state will overseeadditionaltestingofthereservoirearly next year,DeJong and Markle said. Pressure tests showed the reservoir contains superheated.water and steam under pressure of 471 pounds per square inch,Markle said. .Superheated water flashes to steam when the pressure is reduced. A preliminary analysis comparing the cost of developing the geothermal source with Unalaska's hydroelectric potential and present use of diesel fuel for electri- cal generation should be complete by mid-November,he said. Geothermal reservoirs are more typi-cally found at depths of about 6,000 feet, according to Markle,who said the rela- tively shallow depth of the Makushin reservoir would reduce costs of develop- ment drilling and favor the prospects for commercial power generation. Another point in the project's favor,he said,is a relatively low mineral content in the steam,which would trans- late into lower levels of potential air and water pollution from electrical genera-ion. [2e,mam mad * DewREPUBLICGEOTHERMAL,INC.a 11823 EAST SLAUSON AVENUE,SUITE ONE SANTA FE SPRINGS,CALIFORNIA 90670 GERALD W.HUTTRER o (213)945-3661 VICE PRESIDENT BUSINESS DEVELOPMENT TWX 910-586-1696 AND TECHNICAL SERVICES August 2,1983 RECEIVED Ms.Patti DeJong_AUCAlaskaPowerAuthority-4G 0 8 1993 334 West Sth Avenue ALASKA2ndFloor”POWER AUTHORITY Anchorage,AK 99501 Dear Patti: When we recently completed the Phase IB Final Report,we inadvertently neglected to include color photomicrographs for five copies.Enclosed please find five sets of these pictures,to be inserted in the Final Report in place of the Xerox copies originally sent to you. I'm sorry for the inconvenience,but we do believe that the color pictures enhance the report,and we would like to have them in those copies that are given to APA and/or State officials.Thank you for your help. Sincerely, Gerald W.Huttrer Vice President GWH:1jb 3 Enclosures u> : an "5 | Proj.Code.3 Fite Code::0 7)0 3-Vd LY.Date:C3214,J dembotsob :Usaoma REPUBLIC GEOTHERMAL,INC. 11823 EAST SLAUSON AVENUE,SUITE ONE SANTA FE SPRINGS,CALIFORNIA 90670 GERALD W.HUTTRER VICE PRESIDENT BUSINESS DEVELOPMENT AND TECHNICAL SERVICES Ms.Patti DeJong July 27,1983 Alaska Power Authority 334 West 5th Avenue 2nd Floor Anchorage,AK 99501 Dear Patti: (213)945-3661 TWX 910-586-1696 oe,Titan On Tuesday,July 26,1983,20 copies of Republic's Final Phase IB Report for Contract CC-08-2334 were shipped to you. We have amended the Draft Final Report pursuant to many of the comments received from your reviewers,and I trust that the result will be satisfactory. With your concurrence,Republic considers Phase IB to be completed as of this date. Sincerely,on Gerald W.Huttrer Vice President Proj.Cot2.3a. File Code-oF:of.vl 1.Date;3-2051|GATarentony :WEST EYLP Ne Mors fATTENerePORN,Se ES apg ern ar:ian)RSE ee Saale Bat aaa mgt (deh ye a"PRES Res 1982 ENVIRONMENTAL BASELINE DATA COLLECTION PROGRAM FINAL REPORT February 1,1983 Dames begcf oore ee reProj.Coce:oOFiteCode:_3t,07.03_| J.Bote:$32.22-/ 7 ALASKA DIVISION OF GEOLOGICAL &GEOPHYSICAL SURVEYS STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES Proj.Coue:oeriteCode:O6-O1-O8| J,Date:BQ.7 -. oPYolL OA sanra4wil? \.=)Alma,re)wTy October 1982 Alaska Open-file Report 163 HYDROTHERMAL RESOURCES OF THE NORTHERN PART OF UNALASKA ISLAND,ALASKA By J.W.Reeder This report is for sale by DGGS for $l. the four DGGS information offices: Geist Rd.and University Ave.,Fairbanks,99701; Franklin St.,Juneau;and the State Office Bldg.,Ketchikan. orders should be addressed to DGGS,P.O.Box 80007,College,AK 99708. STATE OF ALASKA Department of Natural Resources DIVISION OF GEOLOGICAL &GEOPHYSICAL SURVEYS According to Alaska Statute 41,the Alaska Division of Geological and Geophysical Surveys is charged with conducting 'geological and geophysical surveys to determine the potential of Alaska lands for production of metals,minerals,fuels,and geothermal resources;the locations and supplies of ground waters and construction materials;the potential geologic hazards to buildings,roads,bridges,and other installations and structures;and shall conduct other surveys and investigations as will advance knowledge of the geology of Alaska.' In addition,the Division shall collect,eval- uate,and publish data on the underground,surface, and coastal waters of the state.It shall also process and file data from water-well-drilling logs. DGGS performs numerous functions,all under the direction of the State Geologist---resource investiga-- tions (including mineral,petroleum,and water re- sources),geologic-hazard and geochemical investiga- tions,and information services. Administrative functions are performed under the direction of the State Geologist,who maintains his office in Anchorage (3001 Porcupine Dr.,99501,ph 274-9681). Li It may be inspected at any of Alaska National Bank of the North Bldg., 323 E.4th Ave.,Anchorage; CONTENTS Page TntroductLon..ccercccccceccccccccncceccscev acc ceeseee sere esesnsevesecece 1 Background........ceee05 Coser ere e ence were esc cceesences aac cee n ces en cease 1 AppPlicatlon..ccrecsvecvcccccrcccscassvcnseesseesecsscsserccevnsssscevcese 3 Fumarole fields....ccccccscvccccccccevccccssceccnssccecnssenesscesseseces 3 Geologic Setting..cccccccsccarccccncccccessvccessssessssseesssecsenssecs 5 Hydrothermal resource potential...cress nccccscccccscvccccnssaccscccecce 11 Acknowledgments..ccccccccccncsvccccscnesccessccsseseesseescessesssescess 14 References CIted.cc ccccccccccccnccncccccseseesnecceneseeenesesnnssesenns 16 ILLUSTRATIONS Figure 1.Simplified geologic reconnaissance map of the northern part Of Unalaska Island...ccc ccc cccscccccsccccccsccscsescecs 2 2.The main part of fumarole field 1,looking northeast (July 24,1980)..ccccrcccccccccccccccccccccnccccsvsccvecs 5 3a.Makushin Volcano,looking west-northwest (Feb.27,1982)....6 3b.The main part of fumarole field 2,looking northwest (Aug.8,1980)...cccccnccrcscccnccccccccccevecescsccce 7 4.Part of fumarole field 3,looking northwest (Aug.11,1980).8 5.Part of fumarole field 4,looking east (Aug.8,1980).......9 6.Fumarole field 5,looking west (Aug.12,1980)......sesceece 10° 7. Fumarole field 6,looking northwest (Aug.11,1980).........11 8.Fumarole field 7,looking west (Aug.1968)...........ceecees 12 9a.Fumarole field 8 and Sugarloaf Cone,looking east- northeast (Aug.12,1OBL).ccc cc cccecccccesccccsvscccese oe 13 9b.Old cairn that marks location of fumarole field 8 CJuly 23,1980).ccc caccavnccvancccnccccerccesesccevesvens 14 10.Diagram showing the ratios of major ions of hot-spring waters from Unalaska Island and of hot waters from two exploration wells near Summer Bay on Unalaska Island.....15 TABLE Table 1.<A summary of some of the characteristics of the fumaroles and hot springs of Unalaska Island.......cceccccececccces 4 iit HYDROTHERMAL RESOURCES OF THE NORTHERN PART OF UNALASKA ISLAND,ALASKA By J.W.Reeder INTRODUCTION During DGGS geologic investigations of Unalaska Island in the summer of 1980,previously unreported active fumaroles and hot springs were located in the Makushin Volcano region.To date,eight fumarole fields are known to exist there.Large vapor-dominated hydrothermal reservoirs are suspected to exist in the area of the fumarole fields located on the southeast flank of Makushin Volcano. BACKGROUND The Makushin Volcano of Unalaska Island is one of at least 36 volcanoes on the Aleutian Islands arc that have been reported active since 1760 (Coats, 1950).Volcanic regions such as this,with shallow magma bodies and deep tectonic fracture systems,represent a setting favorable for the existence oflargehydrothermalreservoirs. Active hydrothermal surface manifestations have been known to exist on Unalaska Island for some time.Dall (1897,p.472)stated,"In Unalaska,nearCaptain's Harbor,a thermal spring exists,with a temperature of 94° Fahrenheit,containing sulphur in solution.”This is believed to be the warm spring located near Summer Bay (Reeder,198la),5 km east of the community of Unalaska (fig.1). On rare clear days,a plume from an impressive fumarole field can be seen near the top of Makushin Volcano.This field has received attention in the past because of its known sulfur deposits (Maddren,1919).Early investigations of sulfur deposits throughout this region resulted in the discovery of other hot springs and fumarole fields on the lower flanks of Makushin Volcano.Some of these discoveries are still known (Henry Swanson, R.G.Schaff,and W.E.Long,pers.commun.,1980),even though no written documentation of these early observations have been found.Exploration pitsandcairns(Fig.76)can still be seen at some of the fumarole fields. Drewes and others (1961)observed fumaroles and hot springs on the southern flank of Makushin Voleano.Later,Miller and Smith (1977)suggested that a high-level magma chamber exists under the 3-km-dia summit caldera of the volcano. Warm springs were also reported to exist in the northeastern part of Makushin Valley near Broad Bay (Swanson,pers.commun.,1980).Several large ponds in this region were checked during 1980,but no anomalously warm waters were found.Air reconnaissance in February 1982 showed ponds and swamps devoid of ice and snow in the northeastern part and along the southern edge of Makushin Valley.These unfrozen areas might be due to ground-water seeps at normal ground-water temperatures. -l- - -! 16630" aNs TUDY AREA Pt.Kodia rioat2)Makusti "Voitey 1-5 9°45' Makushin Bay Portage Say Map symbols -----Fault:dashed where approximate Unaltered volcanic rocks e Fumarole field oO Warm or hot spring Plutonic rocks *Recent volcanic vent ey)Caldera Unalaska Formation Figure 1,Simplified geologic reconnaissance map of the northern part of Unalaska Island. The DGGS field party (Reeder,1981b)discovered more active fumarole fields on the flanks of Makushin Volcano,bringing the total fields to eight (numbered clockwise in fig.1). APPLICATION The Unalaska community serves the largest American fishing fleet for the Bering and North Pacific region and it could play a major role in the development of a bottomfish industry.In addition,there is a nearby potential for Outer Continental Shelf oil,gas,and mineral production.Present peak electric utility demands for Unalaska is 15 MW,including both the publicly owned diesel generators and those operated by the private fish processors. Projections for future energy demands are very uncertain,but peak demands by the year 2000 could reach 50 MW.Such energy demands and the previously mentioned observations of fumaroles and hot springs prompted the state (Markle, 1979;Reeder and others,1980a,b)to develop a geothermal exploration plan for Unalaska Island. FUMAROLE FIELDS The Makushin fumarole fields vary in character and size (table 1). Fumarole fields 1-3 consist of fumarolic (boiling-point)activity,of warm ground,and of outcrops of highly hydrothermally altered plutonic and metavolcanic rocks (figs.2-4).Field 4 consists of fumarolic activity in lateral moraine deposits along a stream (fig.5).Pressurized fumarolic activity and warm ground occur in unaltered agglomerates at field 5 (fig.6). A fairly large steam vent and corresponding fumarole field occur near the summit of Makushin Volcano.Part of this field occurs on a small volcanic dome of unknown composition and within the remains of a cinder cone partly covered with sulfur deposits (fig.7).This field (no.6)is located near the center of the 3-km-dia summit caldera of Makushin Volcano.Field 7 consists of fumarolic activity located in andesites covered by pyroclastics and tills (fig. 8).Field 8 consists of minor fumarolic activity,and of hot rock positioned on top of a small knob (fig.9a);the field is located just west of Sugarloaf Cone in a region of unaltered basaltic andesites as based on the classification scheme of Jakes and White (1972)., Some warm and hot springs were found near the fumarole fields at lower elevations (fig.1,table 1).Initial water analyses of some of these hot and warm springs (Motyka and others,1981)indicated near-neutral sodium-bicarbonate-sulfate waters similar to hydrothermal waters described by Mahon and others (1980),which consisted predominantly of meteoric waters that had been heated by vapor-dominated hydrothermal systems generated from greater than 150°C alkali-chloride waters at greater depth.The term 'vapor-dominated hydrothermal systems'was originally coined by White and others (1971)for those systems in which the reservoir fluids are mainly vapor,not liquid;i.e., wet,dry saturated,or superheated steam.The hot springs in the Makushin Volcano region probably derive most of their water from near surface-water or shallow ground-water sources,and most of their heat from the vapor-dominated hydrothermal systems that are the source of the fumaroles throughout the region. -P-Table 1.Some of the characteristics of the fumaroles and hot springs of Unalaska Island. Fumarole {Elevation Types of Approx.area of Max.recorded |Hot Spring Max.recorded temp. Field (meters above |exposed fumarole activity |surface temp.|locations and corresponding ph sea level)rock incl.warm ground |within the for hot springs&assoc.altered j|fumarole field immediately outside bedrock of fumarole field No.1 350 -370 Plutonics and some 3,600 m2 98°C W/in fumarole field,immed 68°C/5+ metavolcanics downslope from field along stream,&upstream from field up to 0.6 km No.2 650 -910 Plutonics and meta-0.30 km2 97°C W/in fumarole field &90°C/5.5+volcanics (solifluct-immed.east of field in ion &landsliding is canyon at 600 m elevationoccurringinfield) No.3 520 -580 Plutonics and meta-0.20 km@ 98°C W/in fumarole field &at 96°C/6+ volcanic several locations down- stream up to a distance of 1.0 km No.4 560 -590 Lateral moraine,vol-4,000 m2 97°C W/in fumarole field (can-- canics &metavolcanics yon to south was not ex- plored &might contain hotspringsand/or fumaroles) No.5 800 -820 Volcanic breccias 4,000 m2 97°C W/in fumarole field &to 71°C/Unknown (agglomerate)southwest by about 0.2 km No.6 1650 -1710 Volcanic dome of un- 0.1 km2 (plus 94°C none found - known composition,0.2 km*regionpyroclastics&sulphur |shows some signsoficefieldthaw) No.7 820 and at Andesites covered by 1000 m2 96°C On the eastern margin of 67°C 860 pyroclastics and tills the lower fumarole field No.8 520 Basaltic andesite 1000 m2 86°C None found - (at 0.25 m depth) Summer 3 Metavolcanics and Main warp spring Two closely located - Bay Warm alluvium about 2m*,Znd 2 springs occur at edge of Springs spring @ 0.25 m -a marsh just SE of Summer(No fum-&warm ground to Bay lake.Max.temp.ofaroles)40 m of springs springs 35°C at pH of 7.0 eyit Srey=As! Figure 2.The main part of fumarole field 1,looking northeast (July 24,1980). Geochemistry indicates that the fumaroles in the Makushin Volcano region are from more than one large vapor-dominated hydrothermal system.In 1980,two shallow exploration wells drilled into unconsolidated deposits near the Summer Ray warm springs encountered an artesian aquifer with a temperature of 50°C and a natural flow rate of 190 lpm (Reeder,198la).The waters from these wells and the main Summer Bay warm spring have similar ratios of major ions (fig. 10),which indicates a common thermal fluid ('parent').By contrast,the waters from the hot springs of the Makushin Volcano region all nave different ratios of major ions (fig.10),which indicates the existence of chemically different vapor-dominated systems.It is also possible (but less likely)that rising vapors are mixing with chemically different shallow ground waters or surface waters to cause different ratios of major ions at the different hot springs. GEOLOGIC SETTING The rocks of Unalaska Island include an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewes and others (1961),a group of intermediate-age plutonic rocks,and a younger group of unaltered volcanic rocks.The three groups can be correlated with those found throughout the eastern and central Aleutian Islands,namely,an early series of a marine volcanic and sedimentary sequence that has been metamorphosed to a greenschist grade,a middle series of plutonic rocks,and a late series of an 5- Figure 3a.Makushin Volcano,looking west-northwest (Feb.27,1982).Fumarole field 2 dominates the foreground,as outlined by thaw region (photograph taken 3 days after a fresh snow).Steam cloud near the summit of volcano marks the location of fumarole field 6. unaltered sequence of Tertiary subaerial volcanic and sedimentary rocks (Marlow and others 1973).The early series is believed by Marlow and others (1973), Scholl and others (1975),and DeLong and others (1978)to be Focene to middle Miocene,53 to 15 m.y.old.The sedimentary and volcanic rocks of the Unalaska Formation found in the Makushin Volcano region have been altered by albitization,chloritization,epidotization,silicification,and zeolitization. The middle series or middle unit consists of plutons mainly of granodiorite that have intruded the early series.These rocks have radiometric dates of 10 to 15 m.y.before present (Marlow and others,1973;DeLong and others,1978). Perfit and Lawrence (1979)argued that the rocks of the Unalaska Formation were altered mainly during the emplacement of these plutonic bodies.The late series,which consists of basaltic and andesitic rocks that unconformably overlie the early and middle series,is up to at least 3 m.y.in age,based on radiometric ages from andesitic magmas (Cameron and Stone,1970). The region southeast of Makushin Volcano consists mainly of rock exposures belonging to the Unalaska Formation,whereas unaltered volcanics make up the Makushin Volcano and most of the rock exposures to the northwest of a line extending from Pakushin Cone to Table Top Mountain (fig.1).Except for Pakushin Cone,the cones contained in the area have been subjected to intense -6- sone?ns key .ar emy Be wa dose Ps wget Eo Sere Dia Figure 3b.The main part of fumarole field 2,looking northwest (Aug.8,1980) glacial erosion.Both the Pakushin and Wide Bay Cones,which lack intense glacial erosion,are suspected to have formed since the last glacial maximum which ended about 11,000 yr ago (Black,1976).The line of cones trending toward Point Kadin (fig.1)and the corresponding extruded lavas are believed by Drewes and others (1961)to have formed within the last several thousand years;they based their claim on the lack of glacial erosion on the cones and flows,and on the degree of development of a submarine bench at Point Kadin. On the basis of the large lichens on the surfaces of some of the scoriaceous andesites exposed on the largest of these explosions craters,these craters are at least several hundred years in age. A fairly thick sequence of pyroclastic deposits,which are similar to the flow type described by Sheridan (1979),occur in three vallevs located in the region roughly outlined by fumarole fields 2 and 7,Bishop Point,Driftwood Bay,and Sugarloaf Cone.These tephras collectively represent a volume of about 0.21 km',about half of which occupies the upper reaches of Makushin Valley just below fumarole field 2 and near fumarole field 1.In the secondlargestdeposit,0.08 km of material ocgupies the valley leading from field 7toBishopPoint.The remainder,0.03 km',occurs in a valley located between fields 7 and 8,and Driftwood Bay.There are other pyroclastic flow deposits in the Makushin Volcano region,such as a deposit between fields 3 and 4,butnoneapproachavolumeofmorethan0.001 km. -7- Figure 4.Part of fumarole field 3,looking northwest (Aug.11,1980). (Photograph courtesy K.E.Swanson). A 60-m-thick section of these pyroclastics is exposed across the creek from fumarole field 1.At the base of this section is a pyroclastic surge deposit at least 6 m thick with antidune bed forms.Glacial tills are exposed between pyroclastics and bedrock just upstream from this exposure,and tills probably underlie this unit at shallow depths.Atop the unit is a l-m-thick ungraded mixture of ash,lapilli,blocks,rounded boulders,and assorted debris.This lahar contains a few plutonic rock fragments.The next unit is : welded tuffaceous agglomerate of up to 3 m thick.The dark gray color and hardness of this unit distinguish it from the other units;andesitic glass blocks are plentiful here.Atop this unit are about six normally sorted ash lapilli flows,each up to 12 m thick.Similar ash-lapilli flow units were recognized at the other two large pyroclastic deposits. Figure 5.Part of fumarole field 4,looking east (Aug.8,1980). } The surfaces ending,the large pyroclastic deposits,which are thought to be related to a large eruption of Makushin Volcano that occurred since the last glacial maximum ending about 11,000 yr ago,slope away from the volcano.The volume of pyroclastic material involved indicates that the eruption was related to the formation of the 3-km-dia Makushin summit caldera.On the basis of the sequence of pyroclastic deposits at fumarole field 1,the eruption probably began as a large vertical eruption cloud which collapsed to form large pyroclastic surges.Following this,enough time elapsed for debris to flow along some the drainages of the volcano.Explosions then destroyed the summit by ejecting large quantities of material into the atmosphere,the caldera collapsed,and large amounts of magma and debris flowed north and east.The lack of soil horizons within this sequence indicates that the deposits were probably formed over a fairly short period of time,certainly no longer than several years. The Unalaska Formation in the region of fumarole fields 1-3 has been extensively intruded by bodies of intermediate plutonic rocks and some gabbro. The bodies and the surrounding Unalaska Formation are extensively fractured, especially along contact boundaries.A common joint system that strikes between N.30°-35°E.with an 80°-90°S.dip in this contact region aligns roughly with fumarole fields 1,2,3,and 8 and with the orientation of many of the valleys.The fractures probably serve as conduits for hydrothermal convection.The hydrothermal surface manifestations of fumarole fields 1 and 2 -9- Figure 6.Fumarole field 5,looking west (Aug.12,1980). (fig.1)are oriented east to northeast along respective northern and southern boundaries of an intervening plutonic body.One prominent near-vertical fracture on the northern boundary of this pluton strikes east-west directly through fumarole field 1. Other near-vertical fractures,striking N.40°-70°W.and appearing to be normal faults,were found near the fumarole fields (fig.1).One fault,which strikes N.60°W.at field 2,extends nearly the entire length of the northern part of Unalaska Island,a distance of over 36 km. The Aleutian arc is part of a ridge-trench system associated with active volcanism and seismicity.The Aleutian Trench is located about 180 km south of Unalaska Island.Global tectonics has the floor of the Pacific Ocean (the Pacific Plate)approaching the Aleutian are (the North American Plate)in a northwesternly direction at a rate of about 7 cm/yr (Minster and others,1974). On the basis of seismic models,the Pacific Plate dips about 30°under the Aleutian arc until it reaches a depth of about 40 km,where its dip increases abruptly to about 70°(Jacob and Hamada,1972);thus,the Pacific Plate at the Aleutian Trench is being thrusted under the North American Plate. This underthrusting causes compressional stresses in the direction of plate convergence in the are region (Nakamura,1977).Therefore,because the Pacific and North American Plates converge at about N.45°W.at Unalaska -10- PORa8pith Figure 7.Fumarole field 6,looking northwest (Aug.11,1980). Island,these near-vertical northwest-striking fractures are suspected to have been caused by compressional tectonic stresses.The fractures,even though they correlate with most of the fumarole fields,do not appear to influence the actual surface configuration of the hydrothermal manifestations.Moreover, they do not appear to serve as conduits for hydrothermal convection,at least not near the ground surface. For Makushin Volcano,Nakamura (1977)determined,on the basis of orientation of flank eruptions,a maximum stress orientation of N.60°W.where the expected azimuth should be about N.45°W.If the expected azimuth is the actual one,the recognized fractures 'striking about N.60°W.should contain a strike-slip component.As shown in figure 1,one N.60°W.fault near the community of Unalaska has such a strike-slip component (based on observed slickensides). HYDROTHERMAL RESOURCE POTENTIAL Large vapor-dominated hydrothermal systems probably exist in the northeast-oriented zone roughly marked by fields 1-4.Lava flows that still retain details of their constructional forms can be found to the a)northwest (flows from the upper reaches of Makushin Volcano and from the prominent rift zone near point Kadin),b)northeast (flows surrounding the Sugarloaf Cone), and c)southwest (the volcanic rocks of the Pakushin Cone).Yet,no such -1ll- Figure 8.Fumarole field 7,looking west (Aug.1968).(Photograph courtesy W.E.Long) deposits have been found within the northeast-orfented zone or in the region to the southeast.In fact,no unaltered volcanic rocks have been recognized as being extruded from this zone,which indicates that no magma extrusions have occurred in this region for the last 3 m.y.3;this is corroborated by the known range of radiometric age dates for unaltered volcanics for the Aleutian arc (Cameron and Stone,1970).A few basaltic and andesitic dikes of unknown age are exposed in the region,but again no corresponding extruded deposits have been found.There have been few,if any,extrusions because the magma probably has not existed at depth.However,there is also the possibility that the magma has been and may still be at depths of several kilometers where it could be more viscous than magmas to the northeast or southwest.If such deep magma bodies exist in the region,they might have a dikelike configuration oriented in a direction corresponding to the N.60°W.fractures shown in figure 1; these bodies and any magma bodies located near the volcanic centers to the west,northwest,and north could be the heat sources for any large vapor-dominated hydrothermal systems. In contrast,any hydrothermal convective systems linked to fumarole fields 5-8 are suspected to be limited to shallow zones,where any heat sources would also be at shallow depths.Such sources might be due to either recent surface -12- |Sugarloaf Cone Fumarole Field No.8.Jo Figure 9a.Fumarole field 8 and Sugarloaf Cone,looking east-northeast (Aug.12,1981).(Photograph courtesy M.J.Larsen.) volcanic flows that still contain heat,as suspected at fumarole field 8,or to the cooling of shallow magma bodies,as reflected by the dome in field 6. Most of the recent extrusive rocks in the northern part of Unalaska Island are porous.Any heat in such rocks have been mostly removed,except for small isolated areas such as the one found at field 8.Hydrothermal convective systems might exist in the fractured Unalaska Formation and corresponding plutonic bodies that are suspected to underlie most of the unaltered volcanic rocks of the northern part of Unalaska Island.However,no real evidence has been found for the existence of such systems.In fact,except for the Summer Bay area near the community of Unalaska (Reeder,198la),no hydrothermal systems are known to exist in the Unalaska Formation beyond the immediate fumarole field regions of Makushin Volcano. A northeast-oriented zone roughly marked by fields 1-4 has been identified as possibly containing large vapor-dominated hydrothermal reservoirs.There are only a few places in the world,such as The Geysers,California,and Larderello,Italy,where hydrothermal systems consist mainly of vapor (White and others,1971).These systems have been developed where they now represent the major source of electrical geothermal power.Further exploration may better define the nature of reservoirs in the Makushin Volcano region,but deep exploratory drilling and well testing such as described by Economides and others (1982)is required to determine their potential. -13- 5 vast Figure 9b.Old cairn that marks location of fumarole field 8 (July 23,1980). ACKNOWLEDGMENTS I thank field assistants Kirk E.Swanson (1980)and Mark J.Larsen (1981) Roman Motyka,Mary Moorman,Shirley Liss,and Malcomb Robb helped with water and gas sampling of the hot springs and funlaroles.I also thank Unalaska residents Abi Dickson,Kathy Grimmes,and the Currier family for their extensive help and advice. The project was funded by the Alaska Power Authority and the U.S. Department of Energy,where these funds were administered by the Alaska Division of Power and Energy Development. -14- -ST-Summer Bay Warm Spring. Well No.1 at Summer Bay. Well No.2 at Summer Bay./\ Hot Spring near Fumarole Field No.1.w ,Hot Spring near Fumarole Field No.2.©° Hot Spring near Fumarole No.3. Hot Spring near Fumarole No.3 (Different spring site) hot waters from two exploration wells near Summer Bay on Unalaska Island. others,1981,and from author.) Figure 10.Diagram showing the ratios of major fons of hot-spring waters from Unalaska Island and of (Data from Motyka and REFERENCES CITED Black,R.F.,1976,Geology of Umnak Island eastern Aleutians as related to the Aleuts:Arctic and Alpine Research,v.8,no.1,p.7-35. Cameron,C.P.,and Stone,D.B.,1970,Outline geology of the Aleutian Islands with paleomagnetic data from Shemya and Adak Islands:University of Alaska Geophysical Institute and Department of Geology,UAG R-213,152 p. Coats,R.R.,1950,Volcanic activity in the Aleutian arc:U.S.Geological Survey Bulletin 974-B,p.35-49. Dall,W.H.,1897,Alaska and its resources:Boston,Lee and Shepard Publishers, 627 p. DeLong,S.E.,Fox,P.J.,and McDowell,F.W.,1978,Subduction of the Kula Ridge at the Aleutian Trench:Geological Society of America Bulletin,v.89, p.83-95. Drewes,Harold,Fraser,G.D.,Snyder,G.L.,and Barnett,H.F.,Jr.,1961, Geology of Unalaska Island and adjacent insular shelf,Aleutian Islands, Alaska:U.S.Geological Survey Bulletin 1028-S,p.583-676. Economides,M.J.,Ogbe,D.0O.,Miller,F.G.,and Ramey,H.J.,Jr.,1982, Geothermal steam well testing,state of the art:Journal of Petroleum Technology,p.976-988. Jacob,K.,and Hamada,K.,1972,The upper mantle beneath the Aleutian Island arc from pure-path Rayleigh-wave dispersion data:Seismological Society of America Bulletin,v.62,p.1439-1453. Jakes,P.,and White,A.J.R.,1972,Major and trace element abundance in volcanic rocks of orogenic areas:Geological Society of America Bulletin, v.83,p.29-40. Maddren,A.G.,1919,Sulphur on Unalaska and Akun Islands and near Stepovak Bay,Alaska:U.S.Geological Survey Bulletin 692,p.283-298. Mahon,W.A.J.,Klyen,L.E.,and Rhode,M.,1980,Neutral sodium/bicarbonate/ suphate hot waters in geothermal systems:Chinetsa (Journal of the Japan Geothermal Energy Association),v.17,no.1 (ser.64),p.11-23. Markle,D.R.,1979,Geothermal energy in Alaska:Site data base and development status:Oregon Institute of Technology,Geo-Heat Utilization Center, 572 p.. Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,Tau Rho,1973, Tectonic history of the central Aleutian arc:Geological Society of America Bulletin,v.84,p.1555-1574. Miller,T.P.,and Smith,R.L.,1977,Geothermal potential of high-level magma chambers in Alaska,in The relationship of plate tectonics to Alaskan geology and resources;Programs and Abstracts:Alaska Geological Society, p-56. Minster,J.B.,Jordan,T.H.,Molnar,P.,and Haines,E.,1974,Numerical modeling of instantaneous plate tectonics:Geophysical Journal of the Royal Astronomical Society,v.36,p.541-576. Motyka,R.J.,Moorman,M.A.,and Liss,S.A.,1981,Assessment of thermal spring sites,Aleutian arc,Atka Island to Becherof Lake-Preliminary results and evaluation:Alaska Division of Geological and Geophysical Surveys _Open-file Report 144,173 p. Nakamura,K.,1977,Volcanoes as possible indicators of tectonic stress orientation- -principle and proposal:Journal of Volcanology and Geothermal Research,v.2,p.1-16. -16- Perfit,M.R.,and Lawrence,J.R.,1979,Oxygen isotopic evidence for meteoric water interaction with the Captains Bay pluton,Aleutian Islands:Earth and Planetary Science Letters,v.45,p.16 22.- Reeder,J.W.,198la,Initial assessment of the hydrothermal resources of the Summer Bay region on Unalaska Island,Alaska:Geothermal Resource Council Transaction,v.5,p.123-126. »1981b,Vapor-dominated hydrothermal manifestations on Unalaska Island,and their geologic and tectonic setting:1981 IAVCEI Symposium - Arc volcanism,Volcanological Society of Japan and the International Association of Volcanology and Chemistry of the Earth's Interior, p.297-298. Reeder,J.W.,Coonrod,P.L.,Bragg,N.J.,Benig-Chakroff,D.,and Markle,D.R., 1980a,Alaska geothermal implementation plan:Draft prepared by the Alaska Department of Natural Resources and the Department of Commerce and Economic Development for the U.S.Department of Energy,108 p. Reeder,J.W.,Motyka,R.J.,and Wiltse,M.A.,1980b,The State of Alaska geothermal program:Geothermal Resource Council Transactions,v.4,p. 823-826. Scholl,D.W.,Duffington,E.C.,and Marlow,M.S.,1975,Plate tectonics and the structural evolution of the Aleutian-Bering Sea region,in Forbes,R.B., ed.,Contributions to the geology of the Bering Sea basin and adjacent regions:Geological Society of America Special Paper 151,p.1-31. Sheridan,M.F.,1979,Emplacement of pyroclastic flows:A review,in Chapin, C.E.,and Elston,W.E.,eds.,Ash-flow tuffs:Geological Society of America Special Paper 180,p.125-136. White,D.E.,Muffler,L.P.J.,Truesdell,A.H.,1971,Vapor-dominated hydrothermal systems compared with hot-water systems:Economic Geology, v.66,no.1,p.75-97. -17- seonmey LapRIa> UNALASKA GEOTHERMAL DEVELOPMENT Michael J.Economides*,John Reeder** and Donald MarkTe*** "University of Alaska,**Division of Geological and Geophysical Surveys***Division of Energy and Power Development ABSTRACT Tere are 88 active volcanoes in tne Aleutian Chain which contatnan extensive geother-mal resource.Geothermal resuurce investiyations have been conducted for the past two years of Unalaska Island.The focus of these investiga- tions have been Maskushin Volcano and Summer Bay, 12 km and 3 km respectively from the town of Unalaska, Shallow drilling operations have discovered a small low temperature resource at Summer Bay. Eight fumarole fields have been located on Makushin Volcano. Further work is now planned with the commit- ment by the State of Alaska to a multimillion dollar resource confirmation program for the Makushin geothermal anomaly.Projected increases of electrical consumption of 40 MW by the year 2000,and the location of $100,000,000 fisheries industry will continue to be driving forces todevelopthisresource. This paper presents the geological,geo- physical and logistical studies for the develop- ment of a geothermal power plant on Unalaska Island of the Aluetian chain, INTRODUCTION Unalaska Island (Figure 1),in the Aleutian Chain,is rapidly becoming the "fish capital"of the United States.Approximately 200 million pounds of crab and fish are processed on the island.Growth in the permanent population,as well as the transient population employed by the processing industry,has been rapid.Demands in mousing,services and utilities have escalatedaccordingly.Present peak electric utility demandis15MW,divided among the publicly owned diesel generators and those operated by the private fish processors. Projections for future demand are risky. While a sizeable portion of the island population appears to be "pro-development"there are promi- nent forces that are apprehensive.The antici- pated sea petroleum exploration activity in the Bering may tax the island's resources significant- ly.Hence,peak demand by the year 2000 could fluctuate between 30 and 60 MW. ,THE UNALASKA GEOLOGY AND THE FUMAROLE FIELDS The rocks of Unalaska Island consist of an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewesetal.,a group of plutonic rocks intermediate in age,and a younger group of unaltered volcanic rocks.Such rock groups can be correlated with rock groups found throughout the eastern and central Aleutian Islands;i.e.,an "early series" consisting mainly of a marine volcanic and sedi- mentary sequence that has been metamorphosed to a greenschist-grade,a "middle series"consistingmainlyofplutonicrocks,and a "late series” consisting of an unaltered sequence of late Ters tiary subaerial volcanic and sedimentary rocks. The region to the southeast of Makushin Volcano consists mainly of rock exposures belonging totheUnalaskaFormation,whereas unaltered vol- canics make up the Makushin Volcano and most oftherockexposurestothenorthwest. Several impressive fumarole fields were ex- amined in the region during the summers of 1980 and 1981.They have been arbitrarily numbered for identification purposes in a clockwise direc- tion.”Figure 2 illustrates the North portion of Unalaska and the position of the discovered fumarole fields.: Initial water analyses of some of these hot and/or warm springs indicate near neutral sodium/bicarbonate/sulphate waters similar 0 hydrothermal waters fournd in greater than 150°C maximum temperature hydrothermal gystems asso-ciated with volcanic arcs elsewhere. These fumarole end hot spring fields vary somewhat in character and dimension.More speci- fically,Fumarole field no.3 consists of vapor- dominated fumarolic activity (i.e.,at boilingpoint),a mudpot,and highly hydrothermally altered ground,covering approximately a 400°by 200'region.About 1000 feet upstream from the west edge of this region and at a slightly lower elevation,warm springs and smal!seeps occurhavingamaximumrecordedtemperatureof65°C. These springs drain into a fairly Jarge pondhavingatemperatureofabout20°C.Fumerole field no.2 consists of vapor-dominated hydro- earnsRare Economides et al, thermal activity covering a region about 3000feetlongandupto1300feetwide.On thesoutheastsideofthisfumarolefieldneara stream channel,several hot springs gecur havingamaximumrecordedtemperatureof87°C.Fumarole field no.3 consists of vapor-dominated hydro- thermal activity covering a region about 1600 feet long and about 500 feet wide.The main fumarole activty is actually concentrated in a region 800 feet long and about 300 feet wide. About 1300 feet downslope to the south of this field exists several hot springs having a maximum recorded temperature of 94°C.Several more hot springs occur about 1000 feet further south along a creek having a maximum recorded temperature of77°C.Fumarole field no.4 consists of vapor- dominated hydrothermal activity covering a narrow region only about 200 feet long,positioned along a stream and lateral moraine.Fumarole field no. 5 consists of vapor-dominated hydrothermal activi- ty covering an area having a diameter of about300feet.A warm spring exists about 600 feet downslope in the southwest direction.The impres- sive and noisy field on the top of Makushin Volcano occupies a 300 feet diameter region.This field occupies an ice covered region showing signs of subsurface thawing covering a region 3000 feet long and 1500 feet wide.A narrow region about 1400 feet long contains sulphur deposits.Field no.7?and 8 both occupy very small areas. The Unalaska Formation in the region of fields no.1,no.2 and no.3 has been extensive- ly intruded by plutonic bodies of gabbro and/or intermediate plutonic rocks.These intrusive bodies and the surrounding Unalaska Formation are severely fractured especially along contact bound- aries.For:example,a small plutonic body oc- cupies the region between fields no.2 and no.3 and extends for several kilometers in a NE direc- tion.The hydrothermal surface manifestations of fields no.2 and no.3 are oriented in general in a NE direction along the contact of this plutonic body and the Unalaska Formation.There is evi- dence of a forceful instrusion of this plutonic body and extensive fracturing along this contact is expected.Unaltered "andesitic and basaltic" volcanic rocks and volcanoclastics lie unconform- ably over the Unalaska Formation in the vicinity of fields no.1,no.2 and no.3.In all three cases,these unaltered rocks are located just upslope of the fields in a direction toward Makushin Volcano.All of the other fields occur in regions consisting of unaltered volcanic rocks where fields no.4 and no.7 are covered with glacial tills.The Unalaska Formation and plu- tonic bodies in this area are suspected to immedi- ately underlie all of these other fields except for fields no.6 and no.8.In the case of field no.8,a small body of hot magma is suspected at a very shallow depth,but the Unalaska Formation and/or plutonic rocks probably occur at this site at least at depths greater than 1000 feet below the ground suface. Just north of the field no.2 and in the vicinity of field no.1%is a sequence of pyroclastic flow deposits positioned on top ofglacialtills.Although the thickness of this sequence of recent phyroclasitc deposits varies throughout the valley,its surface is fairlysmooth,stoping away from Makushin Volcano.In the vicinity of field no.1,the base of the sequence consists of a welded breccia flow about 4 to 8 feet thick,containing chunks of black "dacitic”glass as large as 20 cm in diameter, dark ""andesitic”scoria and pumice.The unit above consists of pumice and scoria chunks as large as 15 cm in diamter in a matrix of lithic fragments and ash,and contains a few blocks as large as 10 feet in diameter.This unit has some crude layering,believed to be flow structures, and is about 300 feet in thickness. Other thick phyroclastic units were ob- served to the north and northeast of Makushin Volcano.A similar but much thinner sequence of pyroclasitc deposits was found between fields no. 2 and 3 on the south side of Makushin Volcano. At present,these phyroclastic deposits are suspected to be related to a caldera forming event that occurred since the last glacial maxi-mum which ended about 11,000 y.b.p. ,and which may be related to the formation of the existing1.5 mile diameter Makushin summit =caldera.Makughin Volcano has erupted 14 times since1760.The last eruption occurred in 1938. 0 Several faults striking between N 40°W to N70-W were found near the vicinity of the fumarole fields.Two of these faults which strike about N60Wextendnearlytheentirelengthofthe northern part of Unalaska Island,a distance of over 36 KM,and are considered to be presently active since they disrupt soil horizons.These two faults bound the largest fumarole field in the region. Due to the underthrusting of one plate under another,such as is presently occurring at the Aleutian trench,compressional stresses in the direction of plate convergence yill exist inthearcregionoftheupperplate.”Since frac- tures and dikes tend to propagate in a direction normal to the minimum principal stress,their general orientation should reflect the direction of grax imum horizontal compression.Nakamura etal.”determined the direction of the prinicpal tectonic stress based on the orientation of flank eruptions on volcanoes for the Aleutian volcanic arc.Their findings roughly correlate with the relative motion between the Pacific and North America Plates.For Makushin Volcano,Nakamuraetal.9 determined a maximum stress orientationof,N 60°W where the expected asimuth was about N45°W.If the expected N 45°W asimuth is the actual correct one,then the recognized normalfaultsstrikinginamoreN60°W direction should also contain a strike-slip component. The hydrothermal systems are expected to extend throughout a much larger area than actual- ly indicated by the observed active hydrothermal manifestations.For example,the hillsides mae tneoughout the region southeastof Makushin Vol-cand Contain aumerous areas of highly altered country rock,which is relic of past hydrothermal activity.In addition,some hydrothermal systems may be capped by less permeable unaltered vol- canics,and thus may not be represented by active surface hydrothermal manifestations.On the other extreme,not all and possibiy none of the fields observed in 1980 and 198}are necessarily con- nected at depth.Instead,several hydrotherma)systems are expected,being driven by individualmagmabodiesorientedinanexpectedN60°W direc- tion. ISLAND LOGISTICS AND GEOTHERMAL POWER PLANT ECONOMICS The approaches to the fumarole fields and hence to the potential power plant site are cum- bersome.An abandoned military airstrip,3500 feet by 100 feet,is located at Driftwood Bay. It is expected that this airfield will serve as logistical base for the planned drilling program,The surface of the airstrip is currently in fair condition but it can be upgraded in a short period of time to receive incoming traffic. Approximately 6 miles from the end of the runway is Sugar Loaf.An existing road connects the two;however,the road is washed out at various places and considerable repairs are neces- sary. Barge transport is possible.Special land- ing craft should be utilized if Driftwood Bay is to be the landing site.Rocky shores and high surf may hinder the landing operations. Transmission lines to Unalaska/Dutch Harbor following the construction of the power plant must be helicopter installed.Underwater cable is expected for the final portion of the lines. Construction costs on Unalaska are signifi- cantly higher than elsewhere in the United States.Drilling costs,because of the cumbersome logistics,are expected to be twice the level of established sites such as in the Greysers or in the Imperial Valley.Table 1 presents a best estimate scenario for a 30 MW geothermal power plant on Unalaska Island.A conservative estimate of 50%dry holes is assumed. A Transmission line,16 miles long,and a connecting 16 mile gravel road are assessed to the cost of a power plant. An average geothermal well,producing 200,000 Ib/hr of steam (either superheated or separated)can support a 10 MW maximum capacity power plant.Hence,considering the high costs to access the formation,estimates for various sizes of power plants (over 10 W)are presented on Table 2,Al?power plant cost estimates include a 5S MW standard generator,a transformer station to handle $5 MW ,and 16 miles of transmission line and access road. Economides et al. The rationale tehind the assessment is the anticipated electric utility demand for tneIslandoverthenextthreedecades.Installation of the higher capacity hardware will necessitate onty infield drilling to boost sagging well out-put or increase capacity as the demand escalates. As expected,the installed cost per MW declines dramatically at higher power plant capa- city since the initial construction and access costs are distributed more evenly. Annual operating costs for a geothermal power plant are showing a much smoother trend. Table 3 presents the estimated annual costs (in 1981 dollars)for various sizes of geothermal power plants. In the case of an Unalaska geothermal power plant,with all the prohibitive construction, drilling and transmission costs,a close compari- son between this and other alternatives is neces- sary.Presently,the electric power generation derives almost exclusively from diesel units. While a variety of power plants exists (all com-mercial processors own private units)an economicincentivemayindicateconsolidation.Larger units cost proportionally less than several smaller units. Table 4 presents the capital and operatingcostsforvarioussizesofdieselpowerplants(in 1981 dollars)for Unalaska Island.The fuel cost is set at $1.40/gatlon.While all other costs are expected to follow the general infla- tionary trends,both the supply and price of diesel,are unpredictable.A U.S.Bureau of Mines report',published in 1975 compared a 2 MW geo- thermal power plant with a 2 MW diesel unit for Unalaska Island.In addition to the obvious fallacies (an 8000 ft well,and 16 miles of transmission lines and road were assessed against a 2 MW geothermal plant),the cost of fuel was given as 41¢per gallon.While all other costs escalated by the normal rate of inflation,fuel has increased by a rate several times larger. Hence,the operating costs as shown in Table 4 may be highly underestimated when projected into the future. Finally,a comparison between geothermal and diesel power plants can be made only in terms of same,maximum output sizes.It is obvious that at small sizes,diesel power plants--the high cost of fuel notwithstanding--will be more attrac- tive.Hence,the search is for that capacity (if any)where the high initial logistical costs of geothermal power generation are balanced by the high operating costs of diesel generation. Table 5 presents such comparison.The rates of return listed include only costs at the gate of the power plant.They do not include household system maintenance,in-town transmission and installation and office and support staff.Hence, they are higher than expected but are offerred here for comparison purposes only.Revenues are for sales of 75%of maximum capacity at 15¢/KWh. oonEconomides et al. Depreciation is for a 30 year life while the tax rate is 50%. Figure 3 depicts the "joint"where a geo- thermal power plant appears more attractive than diesel generation. CONCLUSIONS Geothermal development on Unalaska Island appears attractive if the electric utility needs of the island exceed 30 MW.The terrain and the location of the potential geothermal resource will pose significant logistical problems,hence, the design of a large output power plant must follow the resource evaluation and the projection of future needs.The latter point touches on significant social and economic considerations that need to be addressed by the local and state governments. REFERENCES 1.Orewes,H.,Fraser,G.0.,Snyder,G.L.and Barnett,H.F.:"Geology of Unalaska Island and Adjacent Insular Shelf,Aleutian Istands,Alaska",U.S$.Geological Survey Bull.,1028-S,p.5583-»19oT. 2.Marlow,M.S.,Scholl,O.W.,Buffington, E.C.,and Alpha,Tau Rho:"Tectonic History of the Central Aleutian Arc",Geol.Soc. America Bull.,v.84,p.1555-1574,T9573, Reeder,J.W.:"Vapor-Dominated HydrothermalManifestationson Unalaska Island,andtheirGeologicandTectonicSetting",paperpresentedatthe[AVCE!Symposium -ArcVolcanism,Toyko,Sept.2,1981. Mahon,W.A.,Klyen,L.E.,and Rhode,M.: "Neutral Sodium/Bicarbonate/Sulphate Hot Waters in Geothermal Systems”,Chinetsa,v. 17,no.1,p.11-23,1980. Blak,R.F.:"Geology of Unmak Island, Eastern Aleutians as Related to the Aleuts",Arctic and Alpine Research,v.8, no.1,p.7-35,1976. Coats,R.R.:"Volcanic Activity in the Aleutians Arc",U.S.Geological Survey Bull.,974-B,p.35-49,1950. Nakamura,K.:"Volcanoes as Possible Indica- tors of Tectonic Stress Orientation-Princi- ple and Proposal",Jour,Volcanology andGeothermalRes.,v.2,p.1-16,T977. Nakamura,K.,Jacob,K.H.and Davies,J.N.: "Volcanoes as Possible Indicators of Tec- tonic Stress Orientation -Aleutians and Alaska",Pageoph,v.115,p.87-112,1977. Rosenbruch,J.C.and Bottge,R.G.:"Geother- mal Energy:Economic Potential of Three Sites in Alaska",U.S.Bureau of Mines Information Circular 8692,1975. Table 1.Capital Investment for a 30 HW Geothermal Power Plant,Unalaska Island °ITEM :NUMBER DESCRIPTION COST Well 6 8,000 ft.,7 3/4"diameter (assumed 50%dry wells)$12,000,000 Piping -3,000 ft.,8"diameter pipe,installed 250,000 Road -3000 ft.of service road,18-ft-wide gravel,at $200,000/mile 115,000 Generator 55 MW maximum capacity generator,installed 20,000,000 Transformer Station ]55 MW at $30/kW,installed 1,375,000 Transmission Line }1]miles of transmission line overland (helicopter installed),5 miles underwater,$100,000/mile 1,600,000 Road -16 miles of 18-ft gravel road at $200,000/mite 3,200,000 Subtotal $38,500,000 Contingency 10%of capital 3,850,000 Tutal to be depreciated $42,350,000 Economides et al. Table 2,Capital Expenditures for Various Sizes of Geothermal Steam Power Plants SIZE (MW)TOTAL EXPENDITURE (S$)S/MU 10 33,300,000 3,330,000 20 40,000,000 2,000,000 30 42,350,000 1,410,000 40 46,920,000 1,170,000 65 56 ,000 ,000 1,000,000 Table 3.€simated Annual Operating Costs for a Geothermal Power Plant on Unalaska Island PLANT SIZE $1000/YEAR 10 MW 4,502 20 MW 4,97) 30 MW 5,136 40 MW §,455 55 MW 6,091 30_MW_CASE ITEM DESCRIPTION COST ($1000) Employee Compensation 3 Professionals x $50,000,25 Hourly x $40,000 Plus 50%Benefits 1,725 Wells Maintenance 100 Plant Facilities .1%of Generator Cost 200 Piping 20%of Pipe Cost 50 saps Transmission Line 2%of Cost .32 7 ME Road 2%of Cost 64 Fixed Costs 7%of Investment 2,965 TOTAL ANNUAL COSTS 5,136 Table 4.Capital and Operating Costs ($1000)for Diesel Power Plants on Unalaska Island(including generators,transformers,fuel tanks and 10%contingency) SIZE -CAPITAL COST WAGES ($40/kW}FIXED COSTS (7%)FUEL COST (1.40/gal)*TOTAL OPERATING costs 10 MW 8,600 -400 602 5,082 6,084 20 MW 15,400 800 1,078 10,164 12,042 30 MW 20,600 1,200 1,442 15,246 17,888 40 MW 24,100 1,600 1,687 20,328 23,615 55 MW 33,000 2,200 2,310 27,951 32,461 *363,000 gallons/MW/year. Table 5.Comparative Economics of Geothermal and Diesel Power Plants SIZE GEOTHERMAL (ROR)DIESEL (ROR) went 10 MW 9%24% :20 NW 20°27% 30 MW 31%314 40 MW 38°.35% 55 MW 45%36% 30 MW CASE ($1000) GEOTHERMAL OIESEL Revenues 29565 29565 Uperating Costs 5136 17888 bepreciation Valz .667 Cash Flow Before Taxes 23017 11010 Minus 50%Taxes 11509 5505 Cash Flow after Taxes (*fepreciation)12921 6172 Kate oF Keturn 31:gi: Economides,et al yt ANCH.2 Figure1:Some525en,ELEN AeganILLAGE=iVILLAGESomAlaskaPeninsulaPilotPoiatiOyotaoueyePoreNeidenSSKensiewaePorewysem'oS a Cold weatChigait 4 .°ieee7 Sand PointnN4=\yt\h Ot ones +Eee,pre Duteh Harbor wee Re aN ,oetLclde.NV os King CoveKashasa-Qy Falee Pace pimek .106 tee 300tke.of 2 ad Unalasks L --t 1 Jwo..KilometersRm,fC ? Nikotskt pearnc Sea Figure 2:Northern 'Unataska Island, Showing the Posi- tion of the Fuma- role Fields tied qO i .7"cae] 4 t ]| a N+i a 4 ! .!a i Figure 3:Comparative Economics wees 4 a :or Geothermal and Diesel Power 2 J 4 ;Plants on Unalaska Island20LO pode | t 4 ¢ ¢;U -7 'R 14 :N 10-3, 5 i] wm ; o-t,wre t views ee Ly t FT ry -! 19 15 )ay 8 i PURUD CARED Dai sen ome semee Se.O7.os UNALASKA GEOTHERMAL DEVELOPMENT Michael J.Economides*,John Reeder** and Donald MarkTe*** "University of Alaska,**Division of Geological and Geophysical Surveys***Division of Energy and Power Development ABSTRACT Tere are 88 active volcanoes in tne Aleutian Chain which contain an extensive geother-mal resource,Geothermal resuurce investiyations have been conducted for the past two years on Unalaska Island.The focus of these investiga- tions have been Maskushin Volcano and Summer Bay, 12 km and 3 km respectively from the town of Unalaska, Shallow drilling operations have discovered a small low temperature resource at Summer Bay. Eight fumarole fields have been located on Makushin Volcano. Further work is now planned with the commit- ment by the State of Alaska to a multimillion dollar resource confirmation program for the Makushin geothermal anomaly.Projected increases of electrical consumption of 40 MW by the year 2000,and the location of $100,000,000 fisheries industry will continue to be driving forces todevelopthisresource. This paper presents the geological,geo- physical and logistical studies for the develop- ment of a geothermal power plant on Unalaska Island of the Aluetian chain. INTRODUCTION Unalaska Island (Figure 1),in the Aleutian Chain,is rapidly becoming the "fish capital”of the United States.Approximately 200 million pounds of crab and fish are processed on the island.Growth in the permanent population,as well as the transient population employed by the processing industry,has been rapid.Demands in housing,services and utilities have escalated accordingly.Present peak electric utility demand is 15 HW,divided among the publicly owned diesel generators and those operated by the private fish processors. Projections for future demand are risky. While a sizeable portion of the island population appears to be "pro-development”there are promi- nent forces that are apprehensive.The antici- pated sea petroleum exploration activity in the Bering may tex the island's resources significant-ly.Hence,peak demand by the year 2000 could fluctuate between 30 and 60 MW. ,THE UNALASKA GEOLOGY ANDO THE FUMAROLE FIELOS The rocks of Unalaska Island consist of an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewesetal.,a group of plutonic rocks intermediate jin age,and a younger group of unaltered volcanic rocks.Such rock groups can be correlated with rock groups found throughout the eastern and central Aleutian Islands;i.e.,an "early series” consisting mainly of a marine volcanic and sedi- mentary sequence that has been metamorphosed to a greenschist-grade,a "middle series”consisting mainly of plutonic rocks,and a "late series" consisting of an unaltered sequence of late Terstiarysubaerialvolcanicandsedimentaryrocks. The region to the southeast of Makushin Volcano consists mainly of rock exposures belonging totheUnalaskaFormation,whereas unaitered vol- canics make up the Makushin Volcano and most of the rock exposures to the northwest. Several impressive fumarole fields were ex- amined in the region during the summers of 1980 and 198).They have been arbitrarily numbered for identification purposes in a clockwise direc-tion.”Figure 2 illustrates the North portion of Unalaska and the position of the discovered fumarole fields. Initial water analyses of some of these hot and/or warm springs indicate near neutral sodium/bicarbonate/sulphate waters similar ° hydrothermal waters fournd in greater than 150°C maximum temperature hydrothermal gystems asso-ciated with volcanic arcs elsewhere. These fumarole and hot spring fields vary somewhat in character and dimension.More speci- fically,Fumarole field no.1 consists of vapor- dominated fumarolic activity {i.e.,at boiling point),a mudpot,and highly hydrothermally altered ground,covering approximately a 400°by 200'region.About 1000 feet upstream from the west edge of this region and at a slightly lower elevation,warm Springs and small seeps occur having a maximum recorded temperature of 65°C. These springs drain into a fairly large pondhavingatemperatureofabout20°C.Fumerole field mo.2 cansists of vapar-dominated hydro- weyRatspare Economides et al. thermal activity covering a region about 3000feetlongandupto1300feetwide.On thesoutheastsideofthisfumarolefieldneara stream channel,several hot springs gceur havingamaximumrecordedtemperatureof87°C.Fumarole field no.3 consists of vapor-dominated hydro- thermal activity covering a region about 1600 feet long and about 500 feet wide.The main fumarole activty is actually concentrated in a region 800 feet long and about 300 feet wide. About 1300 feet downslope to the south of this field exists several hot springs having a maximum recorded temperature of 94°C.Several more hot springs occur about 1000 feet further south along@creekhavingamaximumrecordedtemperatureof77°C.Fumarole field no.4 consists of vapor- dominated hydrothermal activity covering.a narrow region onty about 200 feet tong,positioned alongastreamandlateralmoraine.Fumarole field no. 5 consists of vapor-dominated hydrothermal activi- ty covering an area having a diameter of about300feet.A warm spring exists about 600 feet downslope in the southwest direction.The impres- sive and noisy field on the top of Makushin Volcano occupies a 300 feet diameter region.This field occupies an ice covered region showing signs of subsurface thawing covering a region 3000 feet long and 1500 feet wide.A narrow region about 1400 feet tong contains sulphur deposits.Field no.7?and 8 both occupy very small areas. The Unalaska Formation in the region of fields no.1,no.2 and no.3 has been extensive- ly intruded by plutonic bodies of gabbro and/or intermediate plutonic rocks.These intrusive bodies and the surrounding Unalaska Formation are severely fractured especially along contact bound- aries.For.example,a small plutonic body oc- cupies the region between fields no,2 and no.3 and extends for several kilometers in a NE direc- tion.The hydrothermal surface manifestations of fields no.2 and no.3 are oriented in general in a NE direction along the contact of this plutonic body and the Unalaska Formation.There is evi- dence of a forceful instrusion of this plutonic body and extensive fracturing along this contact is expected.Unaltered ""andesitic and basaltic” volcanic rocks and volcanoclastics lie unconform- ably over the Unalaska Formation in the vicinity of fields no.1,no.2 and no.3.In all three cases,these unaltered rocks are located just upslope of the fields in a direction toward Makushin Volcano.All of the other fields occur in regions consisting of unaltered volcanic rocks where fields no.4 and no.7 are covered with glacial tills.The Unalaska Formation and plu- tonic bodies in this area are suspected to immedi- ately underlie all of these other fields except for fields no.6 and no.8.Im the case of field no.8,a small body of hot magma is suspected at a very shallow depth,but the Unalaska Formation and/or plutonic rocks probably occur at this site at least at depths greater than 1000 feet below the ground suface. ; Just north of the field no.2 and in the vicinity of field no.1 is a sequence of pyroclastic flow deposits positioned on top ofglacialtills.Although the thickness of this sequence of recent phyroclasitc deposits varies throughout the valley,its surface is fairlysmooth,sloping away from Makushin Volcano.In the vicinity of field no.1,the base of the sequence consists of a welded breccia flow about 4 to 8 feet thick containing chunks of black "dacitic”glass as large as 20 cm in diameter, dark "andesitic”scoria and pumice.The unit above consists of pumice and scoria chunks as large as 15 cm in diamter in a matrix of lithic fragments and ash,and contains a few blocks as large as 10 feet in diameter.This unit has some crude layering,believed to be flow structures, and is about 300 feet in thickness. Other thick phyroclastic units were ob- served to the north and northeast of Makushin Volcano.A similar but much thinner sequence of pyroclasite deposits was found between fields no. 2 and 3 on the south side of Makushin Volcano. At present,these phyroclastic deposits are suspected to be related to a caldera forming event that occurred since the last glacial maxi-mum which ended about 11,000 y.b.p. ,and which may be related to the formation of the existing1.5 mile diameter Makushin summit caldera. Makushin Volcano has erupted 14 times since1760".The last eruption occurred in 1938. 0 Several faults striking between N 40°W to N70-W were found near the vicinity of the fumarole figids.Two of these faults which strike about N60°W extend nearly the entire length of the northern part of Unalaska Island,a distance of over 36 KM,and are considered to be presently active since they disrupt soil horizons.These two faults bound the largest fumarole field in the region. Due to the underthrusting of one plate under another,such as is presently occurring at the Aleutian trench,compressional stresses in the direction of plate convergence will exist inthearcregionoftheupperplate.”Since frac- tures and dikes tend to propagate in a direction normal to the minimum principal stress,their general orientation should reflect the direction of gnaximum horizontal compression.Nakamura etaldeterminedthedirectionoftheprinicpal tectonic stress based on the orientation of flank eruptions on volcanoes for the Aleutian volcanic arc.Their findings roughly correlate with the relative motion between the Pacific and North American Plates.For Makushin Volcano,Nakamuraetal.”determined a maximum stress orientation of JN 60°W where the expected asimuth was about N4S-W.If the expected N 45°W asimuth is the actual correct one,then the recognized normalfaultsstrikinginamoreN60°W direction should also contain a strike-slip component. The hydrothermal systems are expected to extend throughout a much larger area than actual- ly indicated by the observed active hydrothermal manifestations,For example,the hilttsides xa3!wnee throughout the region southeastof Makushin Vol-Cano contain aumerous areas of highly altered country rock,which is relic of past hydrothermal activity.In addition,some hydrothermal systems may be capped by less permeable unaltered vol- canics,and thus may not be represented by active surface hydrothermal manifestations.On the other extreme,not all and possibly none of the fields observed in 1980 and 1981 are necessarily con- nected at depth.Instead,several hydrothermal systems are expected,being driven by individual magma bodies oriented in an expected N 60°W direc- tion. ISLAND LOGISTICS AND GEOTHERMAL POWER PLANT ECONOMICS The approaches to the fumarole fields and hence to the potential power plant site are cum- bersome,An abandoned military airstrip,3500 feet by 100 feet,is located at Driftwood Bay. It is expected that this airfield will serve as logistical base for the planned drilling program.The surface of the airstrip is currently in fair condition but it can be upgraded in a short period of time to receive incoming traffic. Approximately 6 miles from the end of the runway is Sugar Loaf.An existing road connects the two;however,the road is washed out at various places and considerable repairs are neces- sary. Barge transport is possible.Special land- ing craft should be utilized if Driftwood Bay is to be the landing site.Rocky shores and high surf may hinder the landing operations. Transmission lines to Unalaska/Dutch Harbor following the construction of the power plant must be helicopter installed.Underwater cable is expected for the final portion of the lines. Construction costs on Unalaska are signifi- cantly higher than elsewhere in the United States.Orilling costs,because of the cumbersomelogistics,are expected to be twice the level of established sites such as in the Greysers or in the Imperial Valley.Table 1 presents a best estimate scenario for a 30 MW geothermal power plant on Unalaska Island.A conservative estimate of 50%dry holes is assumed. A Transmission line,16 miles long,and a connecting 16 mile gravel road are assessed to the cost of a power plant. An average geothermal well,producing 200,000 Ib/hr of steam (either superheated or separated)can support a 10 MW maximum capacity power plant.Hence,considering the high costs to access the formation,estimates for various sizes of power plants (over 10 MW)are presented oan Table 2.All power plant cost estimates include a 55 MW standard generator,a transformer station to handle 55 MW ,and 16 miles of transmission Tine and access road. Economides et al, The rationale behind the assessment is the antictpated electric utility demand for tneIslandoverthenextthreedecades.Installation of the higher capacity hardware will necessitate only infield drilling to boost sagging well out-put or increase capacity as the demand escalates. As expected,the installed cost per MW declines dramatically at higher power plant capa- city since the initial construction and access costs are distributed more evenly. Annual operating costs for a geothermal power plant are showing a much smoother trend. Table 3 presents the estimated annual costs (in 1981 dollars}for various sizes of geothermal power plants. In the case of an Unalaska geothermal power plant,with all the prohibitive construction, drilling and transmission costs,a close compari- son between this and other alternatives is neces- sary.Presently,the electric power generation derives almost exclusively from diesel units. While a variety of power plants exists (all com-mercial processors own private units)an economicincentivemayindicateconsolidation.Larger units cost proportionally less than several smaller units. Table 4 presents the capital and operatingcostsforvarioussizesofdieselpowerplants(in 1981 dollars)for Unalaska Island.The fuel cost is set at $1.40/gallon.While all other costs are expected to follow the general infla- tionary trends,both the supply and price of diesel,are unpredictable.A U.S.Bureau of Mines report',published in 1975 compared a 2 MW geo- thermal power plant with a 2 MW diesel unit for Unalaska Island.In addition to the obvious fallacies (an 8000 ft well,and 16 miles of transmission lines and road were assessed against a 2 MW geothermal plant),the cost of fuel was given as 41¢per gallon.While all other costs escalated by the normal rate of inflation,fuel has increased by a rate several times larger. Hence,the operating costs as shown in Table 4 may be highly underestimated when projected into the future. Finally,a comparison between geothermal and diesel power plants can be made only in terms of same,maximum output sizes.It is obvious that at small sizes,diesel power plants--the high cost of fuel notwithstanding--will be more attrac- tive.Hence,the search is for that capacity (if any)where the high initial logistical costs ofgeothermalpowergenerationarebalancedbythe high operating costs of diesel generation. Table 5 presents such comparison.The rates of return listed include only costs at the gate of the power plant.They do not include household system maintenance,in-town transmission and installation and office and support staff.Hence, they are higher than expected but are offerred here for Comparison purposes only.Revenues are for sales of 75%of maximum capacity at 15¢/Kwh. eSorEconomides et al. Depreciation is for a 30 year life while the tax rate is 50%. Figure 3 depicts the "joint”where a geo- thermal power plant appears more attractive than diesel generation. CONCLUSIONS Geothermal development on Unalaska Island appears attractive if the electric utility needs of the island exceed 30 MW.The terrain and the Yocation of the potential geothermal resource will pose significant logistical problems;hence, the design of a large output power plant must follow the resource evaluation and the projection of future needs.The latter point touches on significant social and economic considerations that need to be addressed by the local and state governments. REFERENCES 1.Drewes,H.,Fraser,G.D.,Snyder,G.L.and Barnett,H.F.:"Geology of Unalaska Island and Adjacent Insular Shelf,Aleutian Istands,Alaska",U.§.Geological SurveyBull.,1028-S,p.5583-5676,56. 2.Marlow,M.S.,Scholl,O.W.,Buffington, £.C.,and Alpha,Tau Rho:"Tectonic History of the Central Aleutian Arc",Geol.Soc. America Bull.,v.84,p.1555-1574,T9373. Reeder,J.W.:"Vapor-Dominated Hydrothermal]Manifestations on Unalaska Island,andtheirGeologicandTectonicSetting",paperpresentedatthe[IAVCEI Symposium -ArcVolcanism,Toyko,Sept.2,1981. Mahon,W.A.,Klyen,L.E.,and Rhode,M.: "Neutral Sodium/Bicarbonate/Sulphate Hot Waters in Geothermal Systems",Chinetsa,v. 17,no.1,p.11-23,1980. Blak,R.F.:"Geology of Ummak =Isiand,Eastern Aleutians as Related to the Aleuts",Arctic and Alpine Research,v.8, no.1,p.7-35,1976. Coats,R.R.:"Volcanic Activity in the Aleutians Arc",U.S.Geological SurveyBull.,974-B,p.35-49,1950. Nakamura,K.:"Volcanoes as Possible Indica- tors of Tectonic Stress Orientation-Princi- ple and Proposal",Jour,Volcanology andGeothermalRes.,v.2,p.T-16,T9777. Nakamura,K.,Jacob,K.H.and Davies,J.N.: "Volcanoes as Possible Indicators of Tec- tonic Stress Orientation -Aleutians and Alaska",Pageoph,v.115,p.87-112,1977, Rosenbruch,J.C.and Bottge,R.G.:"Geother- mal Energy:Economic Potential of Three Sites in Alaska",U.S.Bureau of Mines Information Circular 8692,1975. Table 1.Capital Investment for a 30 iW Geothermal Power Plant,Unalaska Island 0ITEM.NUMBER DESCRIPTION cost Well 6 8,000 ft.,7 3/4"diameter (assumed 50%dry wells)$12,000,000 Piping -3,000 ft.,8"diameter pipe,installed 250,000 Road -3000 ft.of service road,18-ft-wide gravel,at $200 ,000/mile 145,000 Generator 55 MW maximum capacity generator,installed 20,000,000 Transformer Station 1 55 MW at $30/kW,installed 1,375,000 Transmission Line ]1}miles of transmission line overland (helicopter installed),5 miles underwater,$100,000/mile 1,600,000 Road -16 miles of 18-ft gravel road at $200,000/mile 3,200,000 Subtotal $38,500,000 Contingency 10%of capital 3,850,000 Total to be depreciated $42,350,000 Economides et al. Table 2.Capital Expenditures for Various Sizes of Geothermal Steam Power Plants SEIZE (MW)TOTAL EXPENDITURE (S$)$/MW 10 33,300,000 3,330,000 20 40,000 ,000 2,000 ,000 30 42,350,000 1,410,000 40 46,920,000 1,170,000 55 56,000,000 1,000,000 Table 3.Esimated Annual Operating Costs for a Geothermal Power Plant on Unalaska Island PLANT SIZE $1000/YEAR 10 MW 4,502 20 MW 4,971 30 MW 5,13€ 40 MW 5,455 55 MW 6,091 30 MW CASE ITEM DESCRIPTION cOsT ($1000) Employee Compensation 3 Professionals x $50,000,25 Hourly x $40,000 Plus 50%Benefits 1,725 Wells Maintenance 100 Plant Facilities -1%of Generator Cost 200 Piping 20%of Pipe Cost 50 vanes Transmission Line 2%of Cost 32-ser Road 2%of Cost 64 Fixed Costs 7%of Investment 2,965 TOTAL ANNUAL COSTS 57136 Table 4.Capital and Operating Costs ($1000)for Diesel Power Plants on Unalaska Island (including generators,transformers,fuel tanks and 10%contingency) SIZE -CAPITAL COST WAGES ($40/kW)FIXED COSTS (7%)FUEL COST (1.40/gal)*TOTAL OPERATING COSTS 10 MW 8,600 -400 602 5,082 6,084 20 MW 15,400 800 1,078 10,164 12,042 30 MW 20,600 1,200 1,442 15,246 17,888 40 MW 24,100 1,600 1,687 20,328 23,615 55 MW 33,000 2,200 2,310 27,951 32,461 *363,000 gallons/MW/year. Table 5.Comparative Economics of Geothermal and Diesel Power Plants SIZE GEOTHERMAL (ROR)DIESEL (ROR) are 10 MW 9%24% ”20 MW 20°274 30 MW 31%314 40 MW 38%35% 55 MW 45%36% 30 MW CASE ($1000) GEUTHERMAL OLESEL Revenues 29565 29565 Uperating Costs 5136 17888 Depreciation Walz :667 Cash Flow Before Taxes 23017 11010 Minus 50%Taxes 11509 5505 Cash Flow after Taxes (*hepreciation)1292)6172 wate or KetUrA 3°gl; wae _Economides,et al a ANCH,<7 Figure1:Someor525Km.of the Aleutian VILLAGES a (Islands and the we ye Alaska Peninsula Pilot Poist.{SS -ae,ptPortHeidenvaNYodanaes ovate Port wyalea 4ae”chigeitnySaodPoiotyanaOEfeeprev'oO AN aDutchHarbor.Lb a Ne CoveQo;aescheag-Re Falee Pans of 5 nicek °308 r08 109 . t t t J ¢_ws .Unalasha PanmWOP° Nikolskt " 1 DERING SEA Figure 2:Northern :Unalaska Island, Showing the Posi- tion of the Fuma- role Fields A a .i Figure3:Comparative Economics mat for Geothermal and Diesel Power i ,Plants on Unalaska Island 4A e 1 q u iR108,7 TA CECTHERR POUCA PLEMT j §--DIESEL PORE Pout \ 4): whee,reg Wea re tara rpc -! 10 15 wh 3 38 WA PLPME CRPCLET EVAULATION OF THE MAKUSHIN GEOTHERMAL RESERVOIR,UNALASKA ISLAND Michael J.Economides(1),Chartes_W.Morris(2),and Don A.Campbel}(3) 1.University of Alaska,Fairbanks,AKNowwithDowell-Schlumberger,London 2.Republic Geothermal,Inc.,Santa Fe Springs,CANowwithSchlumbergerOffshoreServices,New Orleans,LA 3.Republic Geothermal,Inc.,Santa Fe Springs,CA ABSTRACT Analysts of an extended flow test of well ST-1 on the flanks of Makushin Volcano indicates an extensive,water-dominated, Naturally fractured reservoir.The reser-voir appears to be capable of deliveringextremelylargeflowswhentappedbyfull-size production wells.A productivityindextnexcessof30,000 Ib/hr/psi1 implies a phenomena I permeability-thickness product,in the range of §00,000 to 1,000,000 mad-ft.° The flowing bottomhole (1,949-foot)temperature of the fluid ts 379°F,which ts lower than the measured static temperature at that depth (395°F).This phenomenon, coupled with an observed static temperaturegradientreversalfromthemaximum399°Fobservedat1,500 feet,indicates that the reservoir proper is located some distance from the well.Presumably it ts at a temperature slightly lower than 379°F and communicates with the wellbore via a high conductivity fracture systen. A material balance calculation yields an estimate of reserves that are capable of sustaining a]1 of the present power needsofthetsland(13+MW peak)with ageothermalpowerplantforseveralhundredyears.Theoretically,a single largediameterwellatthesiteofST-1 could satisfy this requirement. INTRODUCTION Unalaska Island,located in the centra} portion of the Aleutian Chatn has been the site of a multi-year exploration progras for the evaluation of its geothermal energy potential (Figure 1).Makushin Volcano, the 6,680-faot high active volcano, situated on the northern end of the island, has a large number of surface manifesta- tions,including several large fumarole fields. PROJECT LOCATION MAP Following extensive geological,gee- physical,and geochemtcal surveys of the Makushin region,three +1,500-foot tempera-ture gradient holes were sited and drilledinthesummerof1982.The hales and thetr temperature gradients were described byIsselhardt,et al (1983a),who also provided a geothermal resource model of the Makushin geothermal area (Isselhardt,et al,1983b). The heat source of the Makushin geo- thermal system appears to be a buried {igneous intrusion assoctated with thevolcano.The temperature and post-glacial voleantc distributions suggest that the heat source for the system ts not directly beneath the summit,but rather ts offset to the east.The location of the Makushin producing horizon,a fractured diorite, appears to be structurally controlled by a major northeasterly striking fracture zone. In the suamer of 1983,a stratigraphic test well (ST-1)was drilled near one of the 1982 temperature gradient holes (£-1). A steam zone was encountered at 672 feet, followed by a significant fracture at1,945 feet,where the drillstem dropped free for three feet. The 1983 well testing desertbed by Campbell and Economides (1983)confirmed a highly prolific reservoir producing 47,000 lb/hr through three-inch pipe with little or no detectable pressure drawdown. Inadequately sensitive Amerada-type opres- sure instrumentation prevented rigorous. analysis.A productivity index of over 3,000 Ib/hr/psi and a permeability thick- ness of over 50,000 md-ft were inferred.A long flow test in the summer of 1984 was Intended to provide a better estimate of these reservoir parameters as well as demonstrate sustained Flow capability. TEST FACILITIES ANO_INSTRUMENTATION The surface equipment utilized duringthe1984testingwasbasicallythesameas that used in 1983 and described itn the report by Campbell and Economides (1983).Figure 2 shows the surface equipment arrangements utilized during the long-termtestof1984.A relatively simple two- MAKUSHIN WELL TEST EQUIPMENT Led meeweraae!*:={phase ortfice meter and James tube wereinstalledattheendoftheflowlineto measure the flow rate.Upstream and down- Stream orifice pressures were recorded simultaneously with a differential pressure flow meter.The James tube lip pressure was monitored continuously during the flow test utilizing both a test quality pressure gauge and a Barton pressure recordingmeter.In addition,the wellhead pressure and temperature were recorded continuously on Sarton meters throughout the flow test. The orifice plate described above was utilized to calculate the enthalpy of thefluidusingtheempiricalequationdevelopedbyRusselJames(1980). Downhole pressure and temperaturemeasurementswereobtainedusingtwo separate monitoring systems.The pressure monitoring equipment was a capillary tube system which uttlized a gas filled,volu- metric chamber downhole connected to a very small diameter capillary tube with a sur- face recording pressure transducer.This equipment was filled with heltum gas as the pressure transmitting mediums from the bottomhole to the surface transducer.The equipment utilized in this test has an accuracy of approximately +#0.3 pst,with asensitivityof+0.7 psi on the transducer.The temperature measurements were obtained using a thermocouple cable systencompletelyseparatefromthecapillary tube.This required that the temperature data and the pressure data be acquired in separate runs in the well.The thermo- couple was a chromel-alumel,grounded junction-type with an accuracy of »3degreesFandasensitivityof+3/4 of adegreeF.The thermocouple cable and the capillary tube were contained on twoseparatespools.As will be seen in the data discussed later,the pressure data and the temperature data were found to be quite reproducible throughout the flow test (unlike the prior years'data with Amerada- type Instrumentation). FLOW TEST MEASUREMENTS The test of ST-1 consisted of two flow periods of approximately 33,000 lb/hr and 63,000 lb/hr each.'The test rate/wellhead pressure/bottomhole pressure history is shown in Figure 3.The first flow pertod Reeth MAREE CT=4 now wrcphergmh1964 j / i s =,a 3 Sane 0,L ae 'i"=- a+ n., »05 2 =.=e.|oe jetgenPayonfwdtromivone n s -.s a a as a :" ao) lasted 15 days,while the second flowperiodatthehigherratelasted19days.During the 34 days of Flow from ST-1,therewereseveralminorchangesintheflowrate and/or a bypass of the measuring system in order to perform sampling experiments or to modify the flow equipment.However,the test proceeded relatively smoothly,with the two flow rates being maintained at essentially constant conditions throughout their respective test periods. Prior ta the initiation of flow from ST-l,a static temperature profitie of thewellborewasobtainedonJuly3andastaticpressureprofilewasobtainedon July 4,as shown in Figure 4,Thesesurveysclearlyindicatethatthewellhas a steam zone,with the vapor-liquid inter- face located at about 825 feet.Thts is shown by the constant temperature and pres- sure conditions existing in the upper part of the wellbore until very near the surface(#200 feet).Below 825 feet there is aliquidzonewhichincreasesto2maximum temperature of 399°F at the 1,500-foot depth,then shows a slight decline to a temperature of 395°F at the bottom of the wellbore (1,949 feet). FIGURE 4 STATIC TEMPERATURE (JULY 3,1984) ANG PRESSURE (JULY 4,1964}IN ST<4 Terenure coms mA ° ©90 190 100 200 B80 S08 300 <00 ae S00 SED 800 == "=- |} oe oe aay-_|aon omeseret INseesee ©3 103 19)208 Bd WO WO 8 8 OS Oe After flow was initiated onJulyS$,1984,the well stabilized at a flow rate of about 33,000 Ib/hr and this condi- tion was maintained until July 20,1984. Ouring this flow period the pressure tool was left at the bottom of the well (1,949 feet),continuous ly recording bottomhole pressure,except for the times when wellbore pressure and temperature profiles were obtained.Flowing pressure and temperature profiles were obtained on July 6.The results are shown in Figure §.A second §set of pressure/temperature profiles were odtained on July 19,which were exact overlays of the July 6 profiles.About one psi of drawdown was abserved over the 15 days at the low rate. Fallowing the change In the flow to the higher rate of 63,000 Ib/hr on July 20-21, another pressure/temperature profile was obtained (Figure 6).On August 7,1984,a final pressure profile was obtained which was again an exact overlay of the July 21 profile.OQuritng the high-rate flow pertod, the pressure tool was again left at the bottom of the hale continuously recording bottomhole pressure except when profiles were run.An additional one psi of draw- FIGURE 3 FLOWING TEMPERATURE (JULY &1984) ANO PRESSURE (JULY 6,1964}IN ST % TOOTAEOfer @ 3 100 80 208 Be we 3e 0 8 508 30 OO \i we _q 3 we 1008 r-j a 1208 1208-\- -NICiIN- 2000 ---|H NI down was observed during the 19-day highrateperiod.The well was shut-in on August 8,1984,with the pressure tool hanging in the well at bottom.The pres- sure tool recorded buildup data for the next 17 days,showing less than one pst of increase tn bottomhole pressure. FIGURE6FLOWINGTEMPERATURE(JULY 20.{984} ANG PRESSURE (JULY 2%,13984)IN ST-1 Teewutea comms 7 ©50 168 190 200 250 we SSO 100 we S00 8 C0 wLi \. . :LLIN i iN .ES 1900 N J 1808araN- meee ---||\ DISCUSSION AND INTERPRETATION OF RESULTS Although the resolution of the pressure equipment during this test was far supertor to that used during the 1983 test program, §t was again found that the drawdown pressure response in ST-]was extremely small,perhaps beyond the true sensitivity of the instrumentation.It appears that the pressure drawdown during the low-rate flow pertod was on the order of one psi, while the pressure drawdown in ST-1 during the high-flow rate was on the order of two psi.Thus,the productivity index derived from the two flow pertods equals 31,000-33,000 Jb/hr/psi.These values are very large (an order of magnitude more than the ones postulated in 1983),and indicate that the productivity of the Makushin reservoir ts extremely high.Precise calculation of the permeability-thickness product its not possible with these data, although {tt is easy to infer that the value 1s phenomenally large (1.e.,§00,000 to 1,000,000 md-ft). Produced fluid enters the wellbore at the bottom of the well,1,946-1,949 feet, at a temperature of 379°F,which is less than the static temperature in the wellbore at that Jevel (395°F).This indicates that colder water {is entering the well from some other area of the reservoir,probably shallower,along an unknown fracture path. After shut-in,the wellbore re-equilibrates to its static condition.Thus,the fluid density within auch of the wellbore column lightens over a period of time as it returns to a higher static temperature. Because there is essentially only one inflow potnt,however,and pressure bulldup was measured opposite this point,the re-equiltbration of the wellbore fluid density should have no effect on the accuracy of the measured reservoir pres- sure.Therefore,the lack of full pressure recovery (only one pst rather than two)fs not explained by thermal equilibration,bdut father may be attributable to a real decrease in average reservoir pressure. Well Potential The estimation of individual well power potenttal for commercial operations requires the fundamental]assumption that an extensive reservoir can be represented by the flutd properties,initial pressure, temperature,and productivity index derived from slim hole data such as that from ST-1.Given this as a basis,a wellbore flow model yielding wellhead pressure vs rate must first be validated against the Measured slim hole conditions.Once a match is achteved,then wellhead pressure vs rate curves for various commerctal-size wellbore configurations may be generated and related to appropriate power cycles with some degree of confidence. The flow simulator used for thts studywasdevelopedbyIntercomp(1982)and has been used extensively by the industry forgeothermalandgeopressuredwellboreflow calculations for several years.It 1s a vertical,multiphase flow simulator which Incorporates treatment for vartable wel} diameter with depth,heat losses,and noncondensable gases.The *nominal® commercial well conditions arrived at were as follows: Initial Pressure w 494 psig at 1,949 feet Inflow Temperature =379°F at 1,949 feet Salinity =4,000 ppm TDSC02Content=200 pps Productivity Index #=31,500 1b/hr/psi13-3/8 or 16 inch Wellbore Using these conditions,simulator- generated curves for wellhead pressure vs flow rate were constructed for the two different "commercial®wellbore sizes (Figure 7).At a reasonably optimuswellheadpressureof60psia(for power generation from this resource),a flow rate of 1,250,000 to 2,000,000 Ib/hr is predicted,depending on wellbore size. Reserve Estimation Using a Material SalanceCalculation Material balance calculations for largely incompressible systems,such as the one at the Makushin geothermal reservoir, have been developed and used by a number of investigators in the petroleum literature. The inttiating step {!s an expression providing the isothermal compressibility. ce-1 ov (1)¥a T Assuming that the total compressibility ofthesystemisconstant,Equation1 may beintegrated: ¥2 =ecdp (2) yy and because the recovery in terms of reservoir volumes is defined as: Ps V2-¥y °(3) Vy then a combination of Equations 2 and 3 results ins V2-V¥y a eh 2}y The cumulative production in terms of reservoir volumes is,of course,¥2-¥)and,because the fluid 1s considered incompressible,the ratio Vo-¥y (4)Vy may be taken as: ip id which 1$the ratio of the cumulative mass produced to the inttial «mass-in-place. Hence,Equation 4 becomes: Wy 2 e(CAD)1 (5) wee Of the variables tn Equation 5,Wpjstheoneknownwithcertainty.In this Case Wy 1s equal to: HO 5000 ot eg 2h 850000 =1324=4.06x107 Ibs reflecting the two flow periods. The variables contained in the exponential expression consist of the total compressibility of the system and the average reservoir pressure drop observed during the flow period.In this system, the total compressibility ts the sum of the individual rock and fluid compressibilities. ce »Cy >ce (6) Water compressibility 1s normally taken as3x10-5 psi-i,while the compressi- bility of the rock could reasonably rangebetween2x10-5 psi-l and 6 x 10-5 psi-l, depending on the lithology and the elasti- city of the geologic features.For most reservoirs the value of the compressibilityistakenasequalto6x10-5 pst-l. This value will be used here with the knowledge that it could be somewhat higher or lower. The total observed bottomhole pressure drop at ST-1 during the 34 days of the flow test was less than two psi.The subsequent pressure buildup test resulted in less than one psi pressure gain.Both tests indicate an extremely large permeability-thickness product which is conststent with the small pressure differences observed.The total average reservoir pressure drop is assumed to be roughly one psi. Using Equation 5,the itnitial- fluid-in-place may then be calculated: 4.06 x 107 (Sx 10-8 x1)14W yielding Ws 6.8 x 1012 tbs.Given the uncertainties inherent in this calculation,the value of '°W*can be considered order of magnitude only. Nonetheless,assuming a single full- size production well drilled on the site of ST-1 ytelding 1,500,000 Ib/hr (depending on the power cycle used it could generate 7-12 MWe),the longevity of this reservotr ts extremely large relative to the needs of Unalaska Island (currently only about 13 Mw peak).The calculated initial-mass-in- place could deliver this flow rate for over 500 years. CONCLUSIONS Results from the slim hote ST-1 flow test in 1984 confirmed the basic Makushin model of a shallow steam zone overlying a liquid-dominated reservoir in fractured diorite.A flowing temperature at1,949 feet was found to be 379°F.This fluid appears to be entering the wellbore along 2 fracture which brings in colder water than would be expected by the 395°F static temperature of the fracture zone. The flow testing of the well in 1984 proved that the reservoir is potentially highly productive,even with only three feet of fracture interval open to the wellbore. Sustatned flow through a three-inch dta- meter wellbore of 63,000 lb/hr was achieved with less than two psi of pressure drawdown from the initial pressure of 494 psi.This suggests a very =large permeability-thickness value for the reservoir.The well productivity index obtained during this test was approximately30,000 Ib/hr/pst.Wellbore flow modelingIndicatesthatcommerical-size wells should be capable of one to two million 1b/he rates.A material balance calculation indicates a theoretical electricity reservesufficientfortheneedsofthetslandfor several hundred years at current consump-tion rates.In general,the data obtained during the 1984 Flow test ts consistent with the results obtained during the short- term flow test of 1983,and confirms the existence of a substantial resource. REFERENCES 1.Isselhardt,C.F.,et at (1983), "Temperature Gradient Hole Results from Makushin Geothermal Area,Unalaska Island,Alaska,®Geothermal Resources Counct]Transactions,Vol.7,October 1983,pgs.95-98. 2.Isselhardt,C.F..et al (1983b) "Geothermal Resource Model for the Makushin Geothermal Area,Unalaska Island,Alaska.*Geothermal Resources Counei]Transactions,Vol.7,October 1983,pqs.99-102. 3.Campbell,0.A..and Economides,M.J. (1983),°A Sumeary of Geotherma) Exploration and Data from Stratigraphic Test Well No.1,Makushin Volcano, Unalaska Island,*Proceedings of the Ninth Workshop on Geothermal Reservoir Engineering,Stanford University,December 1983,pgs 167-178. 4.James,Russell (1980),"A Choke-Meter for Geothermal Wells Which Measures Both Enthalpy and Flow,*Geothermal Energy,May 1980,pgs.27-30. 5."Vertical Steam-Water Flow in Wells with Heat Transfer ,®Setentific Software-Intercomp,February 1982. ACKNOWLEDGEMENTS a The authors wish to thank the Alaska Power Authority for their support and numerous memebers of Republic's staff for their input to this report. SZ OX O8 ALASKA DIVISION OF GEOLOGICAL &GEOPHYSICAL SURVEYS STATE OF ALASKA DEPARTMENT OF NATURAL RESOURCES October 1982 Alaska Open-file Report 163 HYDROTHERMAL RESOURCES OF THE NORTHERN PART OF UNALASKA ISLAND,ALASKA By J.W.Reeder This report is for sale by DGGS for $1. the four DGGS information offices: Geist Rd.and University Ave.,Fairbanks,99701;323 E. Franklin St.,Juneau;and the State Office Bldg.,Ketchikan. orders should be addressed to DGGS,P.O.Box 80007,College,AK 99708. STATE OF ALASKA Department of Natural Resources DIVISION OF GEOLOGICAL &GEOPHYSICAL SURVEYS According to Alaska Statute 41,the Alaska Division of Geological and Geophysical Surveys is charged with conducting 'geological and geophysical surveys to determine the potential of Alaska lands for production of metals,minerals,fuels,and geothermal resources;the locations and supplies of ground waters and construction materials;the potential geologic hazards to buildings,roads,bridges,and other installations and structures;and shall conduct other surveys and investigations as will advance knowledge of the geology of Alaska.' In addition,the Division shall collect,eval- uate,and publish data on the underground,surface, and coastal waters of the state.It shall also process and file data from water-well-drilling logs. DGGS performs numerous functions,all under the direction of the State Geologist---resource investiga- tions (including mineral,petroleum,and water re- sources),geologic-hazard and geochemical investiga- tions,and information services. Administrative functions are performed under the direction of the State Geologist,who maintains his office in Anchorage (3001 Porcupine Dr.,99501,ph 274-9681). qi It may be inspected at any of Alaska National Bank of the North Bldg., 4th Ave.,Anchorage; CONTENTS Page Introduction.cccsccccccccccnc cece ncn cece veces ec eneseseee seer seseseces l Background.cccccccccccevcccvssvsevscecceccsesecseereceesasecessscessscces 1 APPLlicatLon.cece sccccccccvcvnncecececrcesceeseessesceesecstesesresseeses 3 Fumarole f1e1dsS..ccc ec scenes vcccsccscesccccessseseneseessscessenecees 3 Geologic Setting..cccccrcvccccevccnnsccnccvavcsescccsccssssscsesescseene 5 Hydrothermal resource potential....cwccesssccccccccscssscsenscessccessene 11 Acknowledgments...cccccccccsc ccc cccec cence ccc e sees senses scesccscesseeee 14 References CAtTed.cc crccccccccccccccesesncasseraccccccceesasccsceeececece 16 ILLUSTRATIONS Figure 1.Simplified geologic reconnaissance map of the northern part of Unalaska Tsland.cccrnccccccccccccccccsccccccesccsceces 2 2.The main part of fumarole field 1,looking northeast CJuly 24,1980).cece cccccc neces ccncccccccccccesesesesscce 5 3a.Makushin Volcano,looking west-northwest (Feb.27,1982)....6 3b.The main part of fumarole field 2,looking northwest (Aug.8,1980).ccc ccccccccvascnsccessccccsseneescceses 7 4.Part of fumarole field 3,looking northwest (Aug.11,1980).8 5.Part of fumarole field 4,looking east (Aug.8,1980).......9 6.Fumarole field 5,looking west (Aug.12,1980).....c.eseeeee 10 7.Fumarole field 6,looking northwest (Aug.11,1980).........11 8.Fumarole field 7,looking west (Aug.1968)......ccccececscce 12 9a.Fumarole field 8 and Sugarloaf Cone,looking east- mortheast (Aug.12,LOBL)ccc ccccrnccccccvecccscccccccce 13 9b.Old cairn that marks location of fumarole field 8 CJuly 23,1980).ccccccccsccccccccccccccccccccscccncccsees 14 10.Diagram showing the ratios of major ions of hot-spring waters from Unalaska Island and of hot waters from two exploration wells near Summer Bay on Unalaska Island.....15 TABLE Table 1.A summary of some of the characteristics of the fumaroles and hot springs of Unalaska Island....ccccccccseccccccens 4 iii HYDROTHERMAL RESOURCES OF THE NORTHERN PART OF UNALASKA ISLAND,ALASKA By J.W.Reeder INTRODUCTION During DGGS geologic investigations of Unalaska Island in the summer of 1980,previously unreported active fumaroles and hot springs were located in the Makushin Volcano region.To date,eight fumarole fields are known to exist there.Large vapor-dominated hydrothermal reservoirs are suspected to exist in the area of the fumarole fields located on the southeast flank of Makushin Volcano. BACKGROUND The Makushin Volcano of Unalaska Island is one of at least 36 volcanoes on the Aleutian Islands arc that have been reported active since 1760 (Coats, 1950).Volcanic regions such as this,with shallow magma bodies and deep tectonic fracture systems,represent a setting favorable for the existence of large hydrothermal reservoirs. Active hydrothermal surface manifestations have been known to exist on Unalaska Island for some time.Dall (1897,p.472)stated,"In Unalaska,nearCaptain's Harbor,a thermal spring exists,with a temperature of 94° Fahrenheit,containing sulphur in solution."This is believed to be the warm spring located near Summer Bay (Reeder,198la),5 km east of the community of Unalaska (fig.1). On rare clear days,a plume from an impressive fumarole field can be seen near the top of Makushin Volcano.This field has received attention in the past because of its known sulfur deposits (Maddren,1919).Early investigations of sulfur deposits throughout this region resulted in the discovery of other hot springs and fumarole fields on the lower flanks of Makushin Volcano.Some of these discoveries are still known (Henry Swanson, R.G.Schaff,and W.E.Long,pers.commun.,1980),even though no written documentation of these early observations have been found.Exploration pits and cairns (f9.7b)can still be seen at some of the fumarole fields. Drewes and others (1961)observed fumaroles and hot springs on the southern flank of Makushin Volcano.Later,Miller and Smith (1977)suggested that a high-level magma chamber exists under the 3-km-dia summit caldera of the volcano. Warm springs were also reported to exist in the northeastern part of Makushin Valley near Broad Bay (Swanson,pers.commun.,1980).Several large ponds in this region were checked during 1980,but no anomalously warm waters were found.Air reconnaissance in February 1982 showed ponds and swamps devoid of ice and snow in the northeastern part and along the southern edge of Makushin Valley.These unfrozen areas might be due to ground-water seeps at normal ground-water temperatures. -7-T |5 (t)§10 km Sea 166°30'|oo oooeoeoe 4 4 in g3mo05miBer i a i ; wtf,N\sruov AREA A . usenanoehte Valley -53°45' Makushin Bay owq Portage Bay Map symbols ----- 'Fault:dashed where approximate e Fumarole field ce)Warm or hot spring*Recent volcanic vent a)Caldera Unalaska Formation Unaltered volcanic rocks Plutonic rocks Figure 1,Simplified geologic reconnaissance map of the northern part of Unalaska Island. The DGGS field party (Reeder,1981b)discovered more active fumarole fields on the flanks of Makushin Volcano,bringing the total fields to eight (numbered clockwise in fig.1). APPLICATION The Unalaska community serves the largest American fishing fleet for the Bering and North Pacific region and it could play a major role in the development of a bottomfish industry.In addition,there is a nearby potential for Outer Continental Shelf oil,gas,and mineral production.Present peak electric utility demands for Unalaska is 15 MW,including both the publicly owned diesel generators and those operated by the private fish processors. Projections for future energy demands are very uncertain,but peak demands by the year 2000 could reach 50 MW.Such energy demands and the previously mentioned observations of fumaroles and hot springs prompted the state (Markle, 1979;Reeder and others,1980a,b)to develop a geothermal exploration plan for Unalaska Island. FUMAROLE FIELDS The Makushin fumarole fields vary in character and size (table 1). Fumarole fields 1-3 consist of fumarolic (boiling-point)activity,of warm ground,and of outcrops of highly hydrothermally altered plutonic and metavolcanic rocks (figs.2-4).Field 4 consists of fumarolic activity in lateral moraine deposits along a stream (fig.5).Pressurized fumarolic activity and warm ground occur in unaltered agglomerates at field 5 (fig.6). A fairly large steam vent and corresponding fumarole field occur near the summit of Makushin Volcano.Part of this field occurs on a small volcanic dome of unknown composition and within the remains of a cinder cone partly covered with sulfur deposits (fig.7).This field (no.6)is located near the center of the 3-km-dia summit caldera of Makushin Volcano.Field 7 consists of fumarolic activity located in andesites covered by pyroclastics and tills (fig. 8).Field 8 consists of minor fumarolic activity,and of hot rock positioned on top of a small knob (fig.9a);the field is located just west of Sugarloaf Cone in a region of unaltered basaltic andesites as based on the classification scheme of Jakes and White (1972). Some warm and hot springs were found near the fumarole fields at lower elevations (fig.1,table 1).Initial water analyses of some of these hot and warm springs (Motyka and others,1981)indicated near-neutral sodium-bicarbonate sulfate waters similar to hydrothermal waters described by Mahon and others (1980),which consisted predominantly of meteoric waters that had been heated by vapor-dominated hydrothermal systems generated from greater than 150°C alkali-chloride waters at greater depth.The term 'vapor-dominated hydrothermal systems'was originally coined by White and others (1971)for those systems in which the reservoir fluids are mainly vapor,not liquid;l.e., wet,dry-saturated,or superheated steam.The hot springs in the Makushin Volcano region probably derive most of their water from near surface-water or shallow ground-water sources,and most of their heat from the vapor-dominated hydrothermal systems that are the source of the fumaroles throughout the region.: -P-Table 1.Some of the characteristics of the fumaroles and hot springs of Unalaska Island. Fumarole |Elevation Types of Approx.area of Max.recorded |Hot Spring Max.recorded temp. Field (meters above |exposed fumarole activity |surface temp.|locations and corresponding ph sea level)rock incl.warm ground |within the for hot springs&assoc.altered |fumarole field immediately outside bedrock of fumarole field No.1 350 -370 Plutonics and some 3,000 m2 98°C W/in fumarole field,immed 68°C/5+ metavolcanics downslope from field along stream,&upstream from field up to 0.6 km No.2 650 -910 Plutonics and meta-0.30 km@ 97°C W/in fumarole field &90°C/5 5+volcanics (solifluct-immed.east of field in ion &landsliding is canyon at 600 m elevationoccurringinfield) No.3 520 -580 Plutonics and meta-0.20 km2 98°C W/in fumarole field &at 96°C/6+ volcanic several locations down- stream up to a distance of 1.0 km No.4 560 -590 Lateral moraine,vol-4,000 m2 97°C W/in fumarole field (can-- canics &metavolcanics yon to south was not ex-plored &might contain hotspringsand/or fumaroles) No.5 800 -820 Volcanic breccias 4,000 m2 97°C W/in fumarole field &to 71°C/Unknown (agglomerate)southwest by about 0.2 km No.6 1650 -1710 Volcanic dome of un-0.1 km (plus 94°C none found - known composition,0.2 km*regionpyroclastics&sulphur |shows some signsoficefieldthaw) No.7 820 and at Andesites covered by 1000 m2 96°C On the eastern margin of 67°C 860 pyroclastics and tills the lower fumarole field No.8 520 Basaltic andesite 1000 me B6°C None found - (at 0.25 m depth) Summer 3 Metavolcanics and Main wary spring Two closely located - Bay Warm alluvium about 2m",2nd 2 springs occur at edge of Springs spring @ 0.25 m -a marsh just SE of Summer(No fum-&warm ground to Bay lake.Max.temp.ofaroles)40 m of springs springs 35°C at pH of 7.0 Figure 2.The main part of fumarole field 1,looking northeast (July 24,1980). Geochemistry indicates that the fumaroles in the Makushin Volcano region are from more than one large vapor-dominated hydrothermal system.In 1980,two shallow exploration wells drilled into unconsolidated deposits near the Summer Ray warm springs encountered an artesian aquifer with a temperature of 50°C and a natural flow rate of 190 lpm (Reeder,198la).The waters from these wells and the main Summer Bay warm spring have similar ratios of major ions (fig. 10),which indicates a common thermal fluid ('parent').By contrast,the waters from the hot springs of the Makushin Volcano region all nave different ratios of major ions (fig.10),which indicates the existence of chemically different vapor-dominated systems.It is also possible (but less likely)that rising vapors are mixing with chemically different shallow ground waters or surface waters to cause different ratios of major ions at the different hot springs. GEOLOGIC SETTING The rocks of Unalaska Island include an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewes and others (1961),a group of intermediate-age plutonic rocks,and a younger group of unaltered volcanic rocks.The three groups can be correlated with those found throughout the eastern and central Aleutian Islands,namely,an early series of a marine volcanic and sedimentary sequence that has been metamorphosed to a greenschist grade,a middle series of plutonic rocks,and a late series of an -5- Figure 3a.Makushin Volcano,looking west-northwest (Feb.27,1982).Fumarole field 2 dominates the foreground,as outlined by thaw region (photograph taken 3 days after a fresh snow).Steam cloud near the summit of volcano marks the location of fumarole field 6. unaltered sequence of Tertiary subaerial volcanic and sedimentary rocks (Marlow and others 1973).The early series is believed by Marlow and others (1973), Scholl and others (1975),and DeLong and others (1978)to be Eocene to middle Miocene,53 to 15 m.y.old.The sedimentary and volcanic rocks of the Unalaska Formation found in the Makushin Volcano region have been altered by albitization,chloritization,epidotization,silicification,and zeolitization. The middle series or middle unit consists of plutons mainly of granodiorite that have intruded the early series.These rocks have radiometric dates of 10 to 15 m.y.before present (Marlow and others,1973;DeLong and others,1978). Perfit and Lawrence (1979)argued that the rocks of the Unalaska Formation were altered mainly during the emplacement of these plutonic bodies.The late series,which consists of basaltic and andesitic rocks that unconformably overlie the early and middle series,is up to at least 3 m.y.in age,based on radiometric ages from andesitic magmas (Cameron and Stone,1970). The region southeast of Makushin Volcano consists mainly of rock exposures belonging to the Unalaska Formation,whereas unaltered volcanics make up the Makushin Volcano and most of the rock exposures to the northwest of a line extending from Pakushin Cone to Table Top Mountain (fig.1).Except for Pakushin Cone,the cones contained in the area have been subjected to intense -6- Figure 3b.The main part of fumarole field 2,looking northwest (Aug.8,1980) glacial erosion.Both the Pakushin and Wide Bay Cones,which lack intense glacial erosion,are suspected to have formed since the last glacial maximum which ended about 11,000 yr ago (Black,1976).The line of cones trending toward Point Kadin (fig.1)and the corresponding extruded lavas are believed by Drewes and others (1961)to have formed within the last several thousand years;they based their claim on the lack of glacial erosion on the cones and flows,and on the degree of development of a submarine bench at Point Kadin. On the basis of the large lichens on the surfaces of some of the scoriaceous andesites exposed on the largest of these explosions craters,these craters are at least several hundred years in age. A fairly thick sequence of pyroclastic deposits,which are similar to the flow type described by Sheridan (1979),occur in three vallevs located in the region roughly outlined by fumarole fields 2 and 7,Bishop Point,Driftwood Bay,and Sugarloaf Cone.These tephras collectively represent a volume of about 0.21 km',about half of which occupies the upper reaches of Makushin Valley just below fumarole field 2 and near fumarole field 1.In the secondlargestdeposit,0.08 km of material occupies the valley leading from field 7 to Bishop Point.The remainder,0.03 km',occurs in a valley located between fields 7 and 8,and Driftwood Bay.There are other pyroclastic flow deposits in the Makushin Volcano region,such as a deposit between fields 3 and 4,butnoneapproachavolumeofmorethan0.001 km. -7- Figure 4,Part of fumarole field 3,looking northwest (Aug.11,1980). (Photograph courtesy K.E.Swanson). A 60-m-thick section of these pyroclastics is exposed across the creek from fumarole field 1.At the base of this section is a pyroclastic surge deposit at least 6 m thick with antidune bed forms.Glacial tills are exposed between pyroclastics and bedrock just upstream from this exposure,and tills probably underlie this unit at shallow depths.Atop the unit is a l-m-thick ungraded mixture of ash,lapilli,blocks,rounded boulders,and assorted debris.This lahar contains a few plutonic rock fragments.The next unit is ¢ welded tuffaceous agglomerate of up to 3 m thick.The dark-gray color and hardness of this unit distinguish it from the other units;andesitic glass blocks are plentiful here.Atop this unit are about six normally sorted ash-lapilli flows,each up to 12 m thick.Similar ash-lapilli flow units were recognized at the other two large pyroclastic deposits. eo Fens Sirti :aeeatsfa4g oneSasehueianeees Os RSaraSere arst - gt tab bag panesst _ee shoreOMEnetseeeSpeacere'one Tigger oo esaoaeercallTeeeraiseCESTdtlOeFaeeaeratesdereaaeomene sap st Ee es LP PE abeBo Pe wre id ee ee.Pr eeetnags ap vey a daceert ' =2 a a Syne aa ae a Ps »ate.aid ee testjae&FO d m aa t ees rey wed ors, Figure 5.Part of fumarole field 4,looking east (Aug.8,1980). The surfaces ending,the large pyroclastic deposits,which are thought toberelatedtoalargeeruptionofMakushinVolcanothatoccurredsincethelast glacial maximum ending about 11,000 yr ago,slope away from the volcano.The volume of pyroclastic material involved indicates that the eruption was related to the formation of the 3-km-dia Makushin summit caldera.On the basis of the sequence of pyroclastic deposits at fumarole field 1,the eruption probably began as a large vertical eruption cloud which collapsed to form large pyroclastic surges.Following this,enough time elapsed for debris to flow along some the drainages of the volcano.Explosions then destroyed the summit by ejecting large quantities of material into the atmosphere,the caldera collapsed,and large amounts of magma and debris flowed north and east.The lack of soil horizons within this sequence indicates that the deposits were probably formed over a fairly short period of time,certainly no longer than several years. The Unalaska Formation in the region of fumarole fields 1-3 has been extensively intruded by bodies of intermediate plutonic rocks and some gabbro. The bodies and the surrounding Unalaska Formation are extensively fractured, especially along contact boundaries.A common joint system that strikes between N.30°-35°E.with an 80°-90°S.dip in this contact region aligns roughly with fumarole fields 1,2,3,and 8 and with the orientation of many of the valleys.The fractures probably serve as conduits for hydrothermal convection.The hydrothermal surface manifestations of fumarole fields 1 and 2 -9- Figure 6.Fumarole field 5,looking west (Aug.12,1980). (fig.1)are oriented east to northeast along respective northern and southern boundaries of an intervening plutonic body.One prominent near-vertical fracture on the northern boundary of this pluton strikes east-west directly through fumarole field l. Other near-vertical fractures,striking N.40°-70°W.and appearing to be normal faults,were found near the fumarole fields (fig.1).One fault,which strikes N.60°W.at field 2,extends nearly the entire length of the northern part of Unalaska Island,a distance of over 36 km. The Aleutian arc is part of a ridge-trench system associated with active volcanism and seismicity.The Aleutian Trench is located about 180 km south of Unalaska Island.Global tectonics has the floor of the Pacific Ocean (the Pacific Plate)approaching the Aleutian arc (the North American Plate)in a northwesternly direction at a rate of about 7 cm/yr (Minster and others,1974). On the basis of seismic models,the Pacific Plate dips about 30°under the Aleutian arc until it reaches a depth of about 40 km,where its dip increases abruptly to about 70°(Jacob and Hamada,1972);thus,the Pacific Plate at the Aleutian Trench is being thrusted under the North American Plate. This underthrusting causes compressional stresses in the direction of plate convergence in the are region (Nakamura,1977).Therefore,because the Pacific and North American Plates converge at about N.45°W.at Unalaska -10- Figure 7.Fumarole field 6,looking northwest (Aug.11,1980). Island,these near-vertical northwest-striking fractures are suspected to have been caused by compressional tectonic stresses.The fractures,even though they correlate with most of the fumarole fields,do not appear to influence the actual surface configuration of the hydrothermal manifestations.Moreover, they do not appear to serve as conduits for hydrothermal convection,at least not near the ground surface. For Makushin Volcano,Nakamura (1977)determined,on the basis of orientation of flank eruptions,a maximum stress orientation of N.60°W.where the expected azimuth should be about N.45°W.If the expected azimuth is the actual one,the recognized fractures 'striking about N.60°W.should contain a strike-slip component.As shown in figure 1,one N.60°W.fault near the community of Unalaska has such a strike-slip component (based on observed slickensides). HYDROTHERMAL RESOURCE POTENTIAL Large vapor-dominated hydrothermal systems probably exist in the northeast-oriented zone roughly marked by fields 1-4.Lava flows that still retain details of their constructional forms can be found to the a)northwest (flows from the upper reaches of Makushin Volcano and from the prominent rift zone near point Kadin),b)northeast (flows surrounding the Sugarloaf Cone), and c)southwest (the volcanic rocks of the Pakushin Cone).Yet,no such -1l- Figure 8.Fumarole field 7,looking west (Aug.1968).(Photograph courtesy W.E.Long) deposits have been found within the northeast-oriented zone or in the region to the southeast.In fact,no unaltered volcanic rocks have been recognized as being extruded from this zone,which indicates that no magma extrusions have occurred in this region for the last 3 m.y.;this is corroborated by the known range of radiometric age dates for unaltered volcanics for the Aleutian arc (Cameron and Stone,1970).A few basaltic and andesitic dikes of unknown age are exposed in the region,but again no corresponding extruded deposits have been found.There have been few,if any,extrusions because the magma probably has not existed at depth.However,there is also the possibility that the magma has been and may still be at depths of several kilometers where it could be more viscous than magmas to the northeast or southwest.If such deep magma bodies exist in the region,they might have a dikelike configuration oriented in a direction corresponding to the N.60°W.fractures shown in figure 1; these bodies and any magma bodies located near the volcanic centers to the west,northwest,and north could be the heat sources for any large vapor-dominated hydrothermal systems. In contrast,any hydrothermal convective systems linked to fumarole fields 5-8 are suspected to be limited to shallow zones,where any heat sources would also be at shallow depths.Such sources might be due to either recent surface -12- Sugarloaf Cone Fumarole Field No.8 So , Figure 9a.Fumarole field 8 and Sugarloaf Cone,looking east-northeast (Aug.12,1981).(Photograph courtesy M.J.Larsen.) volcanic flows that still contain heat,as suspected at fumarole field 8,or to the cooling of shallow magma bodies,as reflected by the dome in field 6. Most of the recent extrusive rocks in the northern part of Unalaska Island are porous.Any heat in such rocks have been mostly removed,except for small isolated areas such as the one found at field 8.Hydrothermal convective systems might exist in the fractured Unalaska Formation and corresponding plutonic bodies that are suspected to underlie most of the unaltered volcanic rocks of the northern part of Unalaska Island.However,no real evidence has been found for the existence of such systems.In fact,except for the Summer Bay area near the community of Unalaska (Reeder,198la),no hydrothermal systems are known to exist in the Unalaska Formation beyond the immediate fumarole field regions of Makushin Volcano. A northeast-oriented zone roughly marked by fields 1-4 has been identified as possibly containing large vapor-dominated hydrothermal reservoirs.There are only a few places in the world,such as The Geysers,California,and Larderello,Italy,where hydrothermal systems consist mainly of vapor (White and others,1971).These systems have been developed where they now represent the major source of electrical geothermal power.Further exploration may better define the nature of reservoirs in the Makushin Volcano region,but deep exploratory drilling and well testing such as described by Economides and others (1982)is required to determine their potential. -13- e ane:RARE ab¥.'ob.;Sates"a chet eae Figure 9b.Old cairn that marks location of fumarole field 8 (July 23,1980). ACKNOWLEDGMENTS I thank field assistants Kirk E.Swanson (1980)and Mark J.Larsen (1981). Roman Motyka,Mary Moorman,Shirley Liss,and Malcomb Robb helped with water and gas sampling of the hot springs and funlaroles.I also thank Unalaska residents Abi Dickson,Kathy Grimmes,and the Currier family for their extensive help and advice. The project was funded by the Alaska Power Authority and the U.S. Department of Energy,where these funds were administered by the Alaska Division of Power and Energy Development. -14- -SI-1 Summer Bay Warm Spring. 2 Well No.1 at Summer Bay.60 60 a2 Well No.2 at Summer Bay. 4 Hot Spring near Fumarole Field No.1.Po 6&6 Hot Spring near Fumarole Field No.2. 8 Hot Spring near Fumarole No.3. 7 Hot Spring near Fumarole No.3 (Olfferent spring site) Figure 10.Diagram showing the ratios of major ions of hot-spring waters from Unalaska Island and of hot waters from two exploration wells near Summer Bay on Unalaska Island.(Data from Motyka and others,1981,and from author.) REFERENCES CITED Black,R.F.,1976,Geology of Umnak Island eastern Aleutians as related to the Aleuts:Arctic and Alpine Research,v.8,no.1,p.7=35. Cameron,C.P.,and Stone,D.B.,1970,Outline geology of the Aleutian Islands with paleomagnetic data from Shemya and Adak Islands:University of Alaska Geophysical Institute and Department of Geology,UAG R-213,152 p. Coats,R.R.,1950,Volcanic activity in the Aleutian arc:U.S.Geological Survey Bulletin 974-B,p.35-49. Dall,W.H.,1897,Alaska and its resources:Boston,Lee and Shepard Publishers, 627 p. DeLong,S.E.,Fox,P.J.,and McDowell,F.W.,1978,Subduction of the Kula Ridge at the Aleutian Trench:Geological Society of America Bulletin,v.89, p-83-95. Drewes,Harold,Fraser,G.D.,Snyder,G.L.,and Barnett,H.F.,Jr.,1961, Geology of Unalaska Island and adjacent insular shelf,Aleutian Islands, Alaska:U.S.Geological Survey Bulletin 1028-S,p.583-676. Economides,M.J.,Ogbe,D.O.,Miller,F.G.,and Ramey,H.J.,Jr.,1982, the-Seeiety-ei- Geothermal steam well testing,state of the art:Journal of Petroleum Technology,p.976-988. Jacob,K.,and Hamada,K.,1972,The upper mantle beneath the Aleutian Island are from pure-path Rayleigh-wave dispersion data:Seismological Society of America Bulletin,v.62,p.1439-1453. Jakes,P.,and White,A.J.R.,1972,Major and trace element abundance in volcanic rocks of orogenic areas:Geological Society of America Bulletin, v.83,p.29-40. Maddren,A.G.,1919,Sulphur on Unalaska and Akun Islands and near Stepovak Bay,Alaska:U.S.Geological Survey Bulletin 692,p.283-298, Mahon,W.A.J.,Klyen,L.E.,and Rhode,M.,1980,Neutral sodium/bicarbonate/ suphate hot waters in geothermal systems:Chinetsa (Journal of the Japan Geothermal Energy Association),v.17,no.1 (ser.64),p.11-23. Markle,D.R.,1979,Geothermal energy in Alaska:Site data base and development status:Oregon Institute of Technology,Geo-Heat Utilization Center, 572 p.; Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,Tau Rho,1973, Tectonic history of the central Aleutian arc:Geological Society of America Bulletin,v.84,p.1555-1574. Miller,T.P.,and Smith,R.L.,1977,Geothermal potential of high-level magma chambers in Alaska,in The relationship of plate tectonics to Alaskan geology and resources;Programs and Abstracts:Alaska Geological Society, p-56. Minster,J.B.,Jordan,T.H.,Molnar,P.,and Haines,E.,1974,Numerical modeling of instantaneous plate tectonics:Geophysical Journal of the Royal Astronomical Society,v.36,p.541-576. Motyka,R.J.,Moorman,M.A.,and Liss,S.A.,1981,Assessment of thermal spring sites,Aleutian arc,Atka Island to Becherof Lake -Preliminary results and evaluation:Alaska Division of Geological and Geophysical Surveys _Open-file Report 144,173 p. Nakamura,K.,1977,Volcanoes as possible indicators of tectonic stress orientation---principle and proposal:Journal of Volcanology and Geothermal Research,v.2,p.1-16. 16- Perfit,M.R.,and Lawrence,J.R.,1979,Oxygen isotopic evidence for meteoric water interaction with the Captains Bay pluton,Aleutian Islands:Earth and Planetary Science Letters,v.45,p.16-22.© Reeder,J.W.,198la,Initial assessment of the hydrothermal resources of the Summer Bay region on Unalaska Island,Alaska:Geothermal Resource Council Transaction,v.5,p.123-126. »198lb,Vapor-dominated hydrothermal manifestations on Unalaska Island,and their geologic and tectonic setting:1981 IAVCEL Symposium - Are volcanism,Volcanological Society of Japan and the International Association of Volcanology and Chemistry of the Earth's Interior, p.297-298. Reeder,J.W.,Coonrod,P.L.,Bragg,N.J.,Benig-Chakroff,D.,and Markle,D.R., 1980a,Alaska geothermal implementation plan:Draft prepared by the Alaska Department of Natural Resources and the Department of Commerce and Economic Development for the U.S.Department of Energy,108 p. Reeder,J.W.,Motyka,R.J.,and Wiltse,M.A.,1980b,The State of Alaska geothermal program:Geothermal Resource Council Transactions,v.4,p. 823-826. Scholl,D.W.,Duffington,E.C.,and Marlow,M.S.,1975,Plate tectonics and the structural evolution of the Aleutian-Bering Sea region,in Forbes,R.B., ed.,Contributions to the geology of the Bering Sea basin and adjacent regions:Geological Society of America Special Paper 151,p.1-31. Sheridan,M.F.,1979,Emplacement of pyroclastic flows:A review,in Chapin, C.E.,and Elston,W.E.,eds.,Ash-flow tuffs:Geological Society of America Special Paper 180,p.125-136. White,D.E.,Muffler,L.P.J.,Truesdell,A.H.,1971,Vapor-dominated hydrothermal systems compared with hot-water systems:Economic Geology, v.66,no.1,p.75-97. -17- on THE UNALASKA GEOTHERMAL EXPLORATION PROJECT PHASE IA FINAL REPORT Frc).Code: Fiie Coda:2&.O7.OZ J.Oate:X2./20.L _| a.jan "Tle..7,(f ri!ve aay . Fer,-,o.Gor,de ple FOOd.Te?i 5 BECEIVED OxAPR221982 ALASKA POWER AUTHORITY HYDROTHERMAL RESOURCES OF THE NORTHERN PART OF UNALASKA ISLAND,ALASKA JOHN W.REEDER Department of Natural Resources Division of Geological and Geophysical Surveys Alaska Open-File Report TD Rarwrtol e eeProj.Code: fila Code: INTRODUCTION During regional geologic investigations of Unalaska Island conducted during the summer of 1980,previously unreported active fumaroles and hot springs were located in the Makushin Volcano region.In total,8 fumarole fields are presently known to exist in the region.Large vapor-dominated hydrothermal reservoirs are suspected to exist in the area of the fumarole fields located on the southeast flank of Makushin Volcano. BACKGROUND Unalaska Island is part of the Aleutian Island arc.The Makushin Volcano on Unalaska Island is one of at least 36 volcanoes on this island arc which have been reported active since 1760 (Coats,1950).Such volcanic regions,with shallow magma bodies and deep tectonic fracture systems, represent a favorable setting for the existence of large hydrothermal reservoirs. Active hydrothermal surface manifestations have been know to exist on Unalaska Island for some time.Dall (1897,p.472)stated :"In Unalaska, near Captain's Harbor,a thermal srping exists,with a temperature of 94° Fahrenheit,containing sulphur in solution".This warm spring is believed to be the warm spring located near Summer Bay (Reeder,1981 b)at a distance of approximately 2.75 kms east of the community of Unalaska (Figure 1). With respect to the Makushin Volcano region,during rare clear days a plume from an impressive fumarole field can be easily seen near the top of Makushin Volcano.This field has received attention in the past because of its known sulphur deposits (Maddren,1919).Early investigations of sulphur deposits throughout this region resulted in the discovery of other hot springs and fumarole fields on the lower flanks of Makushin Volcano. Although some of these discoveries are still known (Henry Swanson of Unalaska,pers.commun.,1980;and Ross G.Schaff and William E.Long of DGGS,pers.commun.,1980),no written documentation of these early observations are known.Exploration pits and cairns (Figure 9b)can still be seen at some of the fumarole fields. During volcano investigations by the U.S.Geological Survey in the Aleutian Islands,observations of fumaroles and hot springs were made on the southern flank of Makushin Volcano (Drewes et al.,1961).Later,a high-level magma chamber was suggested to exist under the approximately 3 km diameter summit caldera (Miller and Smith,1977)of this volcano. In addition,warm springs were reported to exist in the northeastern part of Makushin Valley near Broad Bay (Henry Swanson of Unalaska,pers. commun.,1980).Several large ponds in this region were checked during 1980,but no anomalously warm waters were found.During air reconnaissance conducted in February of 1982,ponds and swamps lacking ice and snow,respectively,were found in the northeastern part and along the southern edge of Makushin Valley.These unfrozen regions might be due to groundwater seeps which are at normal groundwater temperatures. )The Unalaska community presently serves the largest American fishing fleet for the Bering and North Pacific region and it could play a major role in the development of a bottomfish industry.In addition there is a nearby potential for outer continental shelf oil,gas,and mineral production. Present peak electric utility demands for Unalaska is 15 MW,including both the publicly owned diesel generators and those operated by the private fish processors.Projections for future energy demands are very uncertain,but peak demands by the year 2000 could reach between 30-60 MW in response to expanding resource industries.Such energy demands and the previously mentioned observations of fumaroles and hot springs prompted Markle (1979)and Reeder et al.(1980 a and b)to develop a geothermal exploration plan for Unalaska Island. During more recent geologic investigations of Unalaska Island,Reeder (1981 a)discovered active fumarole fields on the flanks of Makushin Volcano.A total of eight fumarole fields have been identified.The locations of these fumarole fields are shown in Figure 1,where they have been arbitrarily numbered for identification purposes in a clockwise direction. FUMAROLE FIELDS The Makushin fumarole fields vary in character and dimensions as indicated in Table 1.Fumarole fields no.1,no.2,and no.3 consist of fumarolic activity (i.e.,at boiling point),of warm ground,and of outcrops of highly hydrothermally altered plutonic and metavolcanic rocks (Figures 2, 3,and 4 respectively).Field no.4 consists of fumarolic activity including a region along a stream (Figure5),as well as on a steep slope to the immediate west which consists of altered metavolcanic rocks. Pressurized fumarolic activity and warm ground occur in unaltered agglomerates at field no.5 (Figure 6).A fairly large steam vent and corresponding fumarole field occur near the summit of Makushin Volcano. Part of this field occurs on a small volcanic dome of unknown composition and within the remains of a cinder cone partly covered with sulphur deposits (Figure 7).This field,fumarole field no.6,is located near the center of the 3 km diameter summit caldera of Makushin Volcano.Field no.7 consists of minor activity located in till (Figure 8).Field no.8 consists of minor fumarolic activity and hot rock positioned on top of a small knob (Figure 9a).This field is located just west of Sugarloaf Cone in a region of unaltered basaltic andesites as based on the classification scheme of Jakes and White (1972). ' Some warm and hot springs were found near the fumarole fields at lower elevations as indicated in Figure 1 and Table 1.Initial water analyses of some of these hot and warm springs were done by Motyka et al.(1981). Their results indicated near neutral sodium/bicarbonate/sulphate waters that were similar in chemical character to hydrothermal waters described by Mahon et al.(1980).In the systems described by Mahon,many of the hot spring waters consist predominantly of meteoric waters which have been heated by vapor-dominated hydrothermal systems generated from greater than 150°C alkali-chloride waters at greater depth.The term "vapor-dominated hydrothermal systems"was originally coined by White et al.(1971)which includes the systems in which the reservoir fluids consist mainly of vapor instead of liquid.Such systems would contain wet,dry saturated,or superheated steam.The hot springs in the Makushin Volcano region probably derive most of their water from near surface-water and/or shallow ground-water sources,and derive most of their heat from vapor-dominated (dry steam)hydrothermal systems that are causing the fumaroles throughout the region. The fumaroles in the Makushin Volcano region probably are caused,based on geochemical evidence,not from one large vapor-dominated hydrothermal system but from several.During the summer of 1980,two shallow exploration wells were drilled into unconsolidated deposits near the Summer Bay warm springs (Reeder,1981 b).These wells encountered an artesian aquifer having a maximum recorded temperature of 50°C and a maximum recorded natural flow rate of 50 gpm.The waters from these wells 'and the main warm spring have similar ratios of major ions (Figure 10), indicating a common thermal fluid.The waters from the hot springs of the Makushin Volcano region in contrast all have different ratios of major ions (Figure 10),indicating the existence of chemically different vapor-dominated systems.It is also possible but less likely that mixing is occurring between rising vapors and chemically different shallow ground waters and/or surface waters such that different ratios of major ions result at the different hot springs. GEOLOGIC SETTING The rocks of Unalaska Island include an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewes et al. (1961),a group of plutonic rocks intermediate in age,and a younger group of unaltered volcanic rocks.Such rock groups can be correlated with rock groups found throughout the eastern and central Aleutian Islands;i.e.,an early series consisting mainly of a marine volcanic and sedimentary sequence that has been metamorphosed to a greenschist-grade,a middle series consisting mainly of plutonic rocks,and a late series consisting of an unaltered sequence of Tertiary subaerial volcanic and sedimentary rocks (Marlow et al.,1973).The early series is believed by Marlow et al.(1973),Scholl et al.(1975),and DeLong et al.(1977)to be Eocene to middle Miocene in age;i.e.,53 to 15 m.y.b.p.These altered sedimentary and volcanic rocks of the Unalaska Formation as found in the Makushin Volcano region have been altered by albitization,chloritization, epidotization,silicification,and zeolitization.The middle series or middle unit consists of epizonal plutons mainly of granodiorite composition that have intruded the early series.These rocks have radiometric dates that fall between 10-15 m.y.b.p.(Marlow et al.,1973; and DeLong et al.,1977).Perfit and Lawrence (1979)argued that the rocks of the Unalaska Formation were mainly altered during the emplacement of these plutonic bodies.The late series,consisting of basaltic and andesitic rocks that unconformally overlies the early and middle series, dates from the present back to at least 3 m.y.b.p.as based on radiometric age dates from andesitic magmas (Cameron and Stone,1970). The region to the southeast of Makushin Volcano consists mainly of rock exposures belonging to the Unalaska Formation,whereas unaltered volcanics make up the Makushin Volcano and most of the rock exposures to the northwest of a line connecting Pakushin Cone,Sugarloaf Cone,and Table Top Mountain (Figure 1).All of these cones have been,except for Pakushin Cone,subject to intense glacial erosion.Pakushin Cone,like the Wide Bay Cone,is suspected to have formed since the last glacial maximum which ended about 11,000 y.b.p.(Black,1976).The line of cones trending toward Point Kadin (Figure 1)and the corresponding extruded lavas were believed by Drewes et al.(1961)to have formed within the last several thousand years.Drewes et al.based their claim on the lack of glacial erosion on the cones and flows,and on the degree of development of a submarine bench at Point Kadin.Based on the large lichens on the surfaces of some of the scoraceous andesites exposed on the largest of these explosion craters,these craters must be at least several hundred years in age. A fairly thick sequence of pyroclastic deposits,which are mainly of the flow type as describedby Sheridan (1979),occur in three valleys in the region roughly outlined by fumarole field no.2,fumarole field no.7, Bishop Point,Driftwood Bay,and Sugarloaf Cone.These pyroclastics collectively represent a volume of about 0.21 km3,About 0.10 km?of material occupies the upper reaches of Makushin Valley just below fumarole field no.2 and in the area of fumarole field no.1.The second largest deposit,0.08 km3,occupies the valley leading from fumarole field no.7 toward Bishop Point.The third largest deposit,0.03 km3,occurs in a valley located between:fumarole field no.7,fumarole field no.8,and Driftwood Bay.Other pyroclastic flow deposits have been recognized in the Makushin Volcano region such as the one which has been found 'between fumarole field no.3 and fumarole field no.4.None of these other pyroclastic flow deposits approach even a 0.001 km>volume. A 60 meter thick section of these pyroclastics is exposed just across the creek from fumarole field no.1.At the base of this section is a pyroclastic surge deposit which has antidune bed forms.The thickness of this unit is unknown since its base is not exposed,but it is at least 6 meters in thickness.Because glacial tills are exposed between pyroclastics and bedrock just upstream from this exposure,it is suspected that tills underlie this unit at shallow depths.On top of this unit is an ungraded mixture of ash,lapilli,blocks,rounded boulders,and other rock debris that in places is less than 1 meter in thickness.This debris flow deposit,lahar,contains a few plutonic rock fragments.The next unit is a welded tuffaceous agglomerate that in places is up to 3 meters in thickness.The dark gray color and hardness of this unit make it quite distinct from the other-units.Andesitic glass blocks were found to be plentiful in this unit.On top of this unit is about 6 normally sorted ash-lapilli flows which have unit thicknesses of up to 12 meters.Similar ash-lapilli flow units were recognized at the other two large pyroclastic deposits. The surfaces of the large pyroclastic deposits in the Makushin Volcano region slope away from Makushin Volcano.These deposits are suspected to be related to a large eruption of Makushin Volcano.that occurred since the last glacial maximum of about 11,000 y.b.p.Because of the volume of pyroclastic material involved,this eruption was probably related to the formation of the 3 km diameter Makushin summit caldera.Based on the ,sequence of pyroclastic deposits at fumarole field no.1,this eruption probably began as a large vertical eruption cloud which collapsed to-form large pyroclastic surges.Following this eruption event,enough time elapsed for debris flows to occur along some -of the drainages of the volcano.Then a sequence of explosions,which destroyed the summit by ejecting parts of it into the atmosphere and by caldera forming collapses at the summit,resulted in the large pyroclastic flow deposits.The erupted debris from these summit eruptions was directed more to the north and the east than to the south and the west.Due to the lack of any soil horizons within this sequence of pyroclastic deposits,these deposits probably were formed over a fairly short period of time that could have ranged anywhere between several hours to several years.With respect to any geothermal development in this region,the hazard from future erputions should be addressed. The Unalaska Formationin the region of fumarole fields no.1,no.2,and no.3 has been extensively intruded by plutonic bodies of intermediate plutonic rocks and some gabbro.The instrusive bodies and the surrounding Unalaska Formation are extensively fractured especially along contact boundaries.A common joint system striking between N 30°E and N 35°E with a 80-90°dip to the south in this contact region aligns roughly with fumarole fields no.1,2,3,and 8 as well as with the orientation of many of the valleys.Such fractures probably serve as conduits for hydrothermal convection.A plutonic body occupies the region between fields no.1 and no.2 (Figure 1),where the hydrothermal surface | manifestations of fumarole fields no.1 and no.2 are oriented in an east to northeast direction along the northern and southern boundaries of this plutonic body,respectively.One prominent near vertical fracture on the -9.- northern boundary of this pluton strikes east-west directly through fumarole field-no.1.Such fractures,along the contact,probably serve as conduits near the ground surface for the hydrothermal convection that is driving the fumaroles. Several near vertical fractures,striking between N 40°W and N 70°W and appearing to be normal faults,were found near the vicinity of the fumarole fields as shown in Figure 1.One of these faults,which strikes about N 60°W at field no.2,extends nearly the entire length of the northern.part of Unalaska Island,which is a distance of over 36 km.This fault has been active recently because disrupted soil horizons were found along part of its southeastern length. The Aleutian arc is part of a ridge-trench system associated with active volcanism and seismicity.With respect to the northern part of Unalaska Island,the Aleutian trench is located about 180 km to the south.Based on the theory of global tectonics,the floor of the Pacific Ocean (i.e., the Pacific Plate)is presently approaching relatively the Aleutian arc (i.e.,the North American Plate)in a northwesterly direction at a rate of about 7 cm/year (Minster et al.,1974).Based on seismic models,the Pacific Plate dips about 30°under the Aleutian arc until it reaches a depth of about 40 km where its dip increases abruptly to about 70°(Jacob and Hamada,1972),i.e.,the Pacific Plate at the Aleutian trench is being underthrusted beneath the North American Plate. The underthrusting of the Pacific plate under the North American plate causes compressional stresses in the direction of plate convergence in the arc region as indicated by Nakamura (1977).Because the motion of -10- convergence of the Pacific and North American plates at Unalaska is approximately in a N 45°W direction,these near vertical northwest striking fractures are suspected to have been caused by compressional tectonic stresses.The fractures,even though they correlate with most of the fumarole fields,do not appear to influence the actual surface configuration of the hydrothermal manifestations.These fractures do not appear to serve as conduits for hydrothermal convection at least near the ground surface. For Makushin Volcano,Nakamura et al.(1977)determined,based on the orientation of flank eruptions,a maximum stress orientation of N 60°W where the expected azimuth should be about N 45°W.If the expected azimuth is the actual one,then the recognized fractures striking about N 60°W should contain a strike-slip component.-As shown in Figure 1,one N 60°W striking fault.in the community of Unalaska was found to have such a strike-slip component.as based on observed slickensides. HYDROTHERMAL RESOURCE POTENTIAL It is suspected that large vapor-dominated hydrothermal systems exist in the northeast oriented zone as roughly marked by fields no.1,no.2,no. 3 and no.4.Recent Java flows (i.e.,flows that still retain details of their constructional forms)can be found northwest of this zone as represented by the flows from the upper reaches of Makushin Volcano and from the prominent rift zone near Point Kadin,northeast of this zone as represented by the flows surrounding the Sugarloaf Cone,and southwest of this zone as represented by the volcanic rocks of the Pakushin Cone.Yet, no recent volcanic extrusions have occurred within this northeast oriented -ll- "zone nor from the region to the southeast.In fact no unaltered volcanic rocks have been recognized as being extruded from this zone,indicating that probably no magma extrusions have occurred in this region for the last three million years as based on the known range of radiometric age dates for unaltered volcanics for the Aleutian arc as determined by Cameron and Stone (1970)..Such magma extrusions have not occurred either because the magma does not exist at depth or because magma exists at large depths where it might be more viscous than any magmas to the northeast or the the southwest.If such magma bodies exist in the region,they might have a dike-like configuration oriented in a direction corresponding to the N 60°W fractures shown in Figure 1.Such deep magma bodies as well as any magma bodies located near the volcanic centers to the west,northwest, and north could be the heat sources for any large vapor-dominated hydrothermal systems. In contrast,any hydrothermal convective systems linked to fumarole fields no.5,no.6,no.7,and no.8 are suspected to be limited to shallow zones where any heat sources would also be at shallow depths.Such shallow heat sources might be due to the existence of recent surface volcanic flows that still contain heat as suspected at fumarole field no. 8.Such shallow heat sources also might be due to the cooling of shallow magma bodies as reflected by the dome in field no.6. Most of the recent extrusive rocks (i.e.,volcanic rocks that still show their surface constructional form)in the northern part of Unalaska Island are porous basaltic rocks.Any heat contained in such rocks has been mostly removed,except for small isolated areas such as the one found -12- "at field no.8.Hydrothermal convective systems might exist in the fractured Unalaska Formation and corresponding plutonic bodies which are suspected to underlie most of the unaltered volcanic rocks of the northern part of Unalaska Island.As of yet,no real evidence has been found for the existence of such systems.In fact no hydrothermal systems are known to exist in the Unalaska Formation beyond the immediate fumarole field regions of the Makushin Volcano except at Summer Bay near the community of Unalaska (Figure 1).This particular system does not at present show any substantial promise for geothermal utilization beyond a direct-use type of development (Reeder,1981 b). A northeast oriented zone roughly marked by fields no.1,no.2,no.3,and no.4 has been identified as possibly containing large vapor-dominated hydrothermal reservoirs.There are only a few places in the world,such as The Geysers,California,and Larderello,Italy,where hydrothermal systems consist mainly of vapor instead of liquid (White et al.,1971). Such systems have been developed where they now represent the major source of electrical geothermal power.Although further exploration may better define the nature of such reservoirs in the Makushin Volcano region,deep exploratory drilling along with appropriate well testing such as described by Economides et al.(1980)will be required to make any estimates of the nature and development potential of such geothermal reservoirs. -13- ACKNOWLEDGMENTS During the entire 1980 and 1981 summer field season,I was assisted by Kirk E.Swanson and Mark J.Larsen respectively.Roman Motyka,Mary Moorman,Sirley Liss,and Malcomb Robb helped with water and gas sampling of the hot springs and fumaroles during aproximately a two week visit. Extensive help was received from local residents of Unalaska such as Abi Dickson,Kathy Grimmes and the Currier family. Monies for undertaking this project were received from the Alaska Power Authority and from the U.S.Department of Energy,both being administered through the Alaska Division of Power and Energy Development. -14 - REFERENCES CITED Black,R.F.,1976,Geology of Umnak Island eastern Aleutians as relate to the Aleuts:Arctic and Alpine Research,v.8,no.1,pp.7-35. Cameron,C.P.and Stone,D.B.,1970,Outline geology of the Aleutian Istands with paleomagnetic data from Shemya and Adak islands:Alaska Univ.Geophys.Inst.,UAG R-213,152 p. Coats,R.R.,1950,Volcanic activity in the Aleutian Arc:U.S.Geological Survey Bull.974-B,pp.35-49. Dall,W.H.,1897,Alaska and its resources:Boston,Lee and Shepard, Publishers,627 p. DeLong,S.E.,Fox,P.J.,and McDowell,F.W.,1978,Subduction of the Kula Ridge at the Aleutain Trench:Geological Society of America Bull.,v.89, pp.83-95, Drewes,H.,Fraser,G.D.,Snyder,G.L.,and Barnett,H.F.,1961,Geology of Unalaska Island and adjacent insular shelf,Aleutian Islands,Alaska: U.S.Geological Survey Bull.1028-S,pp.5583-5676. Economides,J.J.,Ogbe,D.O.Miller,F.G.,and Ramey,H.J.Jr.,1980, Geothermal steam well testing:55th Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME,SPE 9272,15 p. Jacob,K.,and Hamada,K.,1972,The upper mantle beneath the Aleutian Island arc from pure-path Rayleigh-wave dispersion data:Bull.of Seismological Society of America,v.62,pp.1439-1453. Jakes,P.,and White,A.J.R.,1972,Major and trace element abundance in volcanic rocks of orogenic areas:Geological Society of America Bull., v.83 pp.29-40. Maddren,A.G.,1919,Sulphur on Unalaska and Akun Islands and near Stepovak Bay,Alaska:U.S.Geological Survey Bull.692,pp.283-298. Mahon,W.A.,Klyen,L.E.,and Rhode,M.,1980,Neutral sodium/bicarbonate/suphate hot waters in geothermal systems:Chinetsa (Journal of the Japan Geothermal Energy Association),v.17,no.1 (Ser. No.64)pp.11-23. Markle,D.,1979,Geothermal energy in Alaska --Site data base and development status:Oregon Institute of Technology,Geo-Heat Utilization Center,572 p. Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,Tau Rho,1973, Tectonic history of the central Aleutian Arc:Geol.Soc.America Bull., v.84,pp.1555-1574 -15- Miller,T.P.,and Smith,R.L.,1977,Geothermal potential of high-level magma chambers in Alaska,in The relationship of plate tectonics to Alaskan geology and resources:Alaska Geological Society,Anchorage, Program &Abstracts,56 p. Motyka,R.J.,Moorman,M.A.,Liss,S.A.,1981,Assessment of thermal spring sites,Aleutian Arc,Atka Island to Becherof Lake -preliminary results and evaluation:Alaska Div.of Geological &Geophysical Surveys, Alaska Open-File Report 144,173 p. Minster,J.B.,Jordan,T.H.,Molnar,P.,and Haines,E.,1974,Numerical modeling of instantaneous plate tectonics:Geophy.Jour.Royal Astr. Soc.,v.36,pp.541-576, Nakamura,K.,1977,Volcanoes as possible indicators of tectonic stress orientation --principle and proposal:Jour.Volcanology and Geothermal Res.,Ve 2 pp.1-16. Perfect,M.R.,and Lawrence,J.R.,1979,Oxygen isotopic evidence for meteoric water interaction with the Captains Bay pluton,Aluetian Islands: Earth and Planetary Science Letters,v.45,pp.16-22. Reeder,J.W.,Coonrod,P.L.,Bragg,N.J.,Benig-Chakroff,D.,and Markle, D.R.,1980 a,Draft - -Alaska Geothermal implementation plan:Report prepared by the State of Alaska Dept.of Nat.Resources and the Dept.of Commerce and Economic Development for the U.S.Dept.of Energy.108 p. Reeder,J.W.,Motyka,R.J.,and Wiltse,M.A.,1980 b,The State of Alaska geothermal program:Geothermal Res.Council,Trans.,v.4,pp.823-826. Reeder,J.W.,1981 a,Vapor-dominated hydrothermal manifestations on Unalaska Island,and their geologic and tectonic setting:1981 IAVCEI Symposium -Arc Volcanism,The Volcanological Soc.of Japan and the Int'l. Assoc.of Volcanology and Chemistry of the Earth's Interior,pp.297-298. Reeder,J.W.,1981 b,Initial assessment of the hydrothermal resources of the Summer Bay region on Unalaska Island,Alaska:Geothermal Res.Council,Trans.,v.5,pp.123-126. 'Scholl,D.W.,Duffington,E.C.,and Marlow,M.S.,1975,Plate tectonics and the structural evolution of the Aleutian-Bering Sea region,in The geophysics and geology of the Bering Sea region:Geol.Soc.of America, Spec.Paper 151,pp.1-31. Sheridan,M.F.,1979,Emplacement of pyroclastic flows:A review,in Chapin,C.E.and Elston,W.E.,eds.,Ash-flow tuffs:Geological Soc.of America,Spec.Paper 180,pp.125-136. White,D.E.,Muffler,L.P.J.,Truesdell,A.H.,1971,Vapor-dominated hydrothermal systems compared with hot-water systems:Economic Geology, ve 66,no.1,pp.75-97, -16 - TABLE 1.A summary of some of the characteristics of the fumaroles and hot springs of Unalaska Island. Fumarole |Elevation Types of Approx.area of |Max.recorded |Hot Spring Max.recorded tenp.Field (meters above |exposed fumarole activity |surface tenp.|locations and corresponding phsealevel)|rock incl.wam ground |within the for hot springs&assoc.altered |fumarole field immediately outsidebedrockoffumarolefield No.1 350 -370 Plutonics and some 3,000 m2 98°C W/in fumarole field immed.68°C/5+metavolcanics -downslope fran field along strean &upstrean fran field up to 0.25 km but still at lower elevation No.2 650 -910 Plutonics and meta-0.40 km2 97°C W/in furarole field &90°C/5.5+ volcanics (solifluct-immed.east of field in ion &landsliding is canyon at 600 m elevation occurring in field)- No.3 520 -580 Plutonics and meta-0.20 km2 98°C W/in fumarole field &at 96°C /6+ volcanic several locations down- strean up to a distance of 1.0 km No.4 560 -590 Lateral moraine,vol-4,000 m2 97°C W/in fumarole field (can - canics &metavolcanics yon to south was not ex- plored &might contain hot springs) No.5 800 -820 Volcanic breccias 4,000 me 97°C W/in fumarole field &to Hot to hand/(agglanerate)southwest by about 0.25 km unknown TABLE 1.(Continued) Fumarole |Elevation Types of Approx.area of |Max.recorded |Hot Spring Max.recorded tenp. Field (meters above |exposed fumarole activity |surface tenp.|locations and corresponding ph sea level)|rock inc].warm ground |within the for hot springs &assoc.altered |fumarole field immediately outside bedrock of fumarole field No.6 1650 -1710 |Volcanic done of un-25,000 m2 94°C none found - known conposition,(0.25 km2 regionpyroclastics&sulphur |shows some signsoficefieldthaw No.7 1040 Tills and possibly 40 m2 -None found - pyroclastics No.8 520 Basaltic andesite 1200 n@ 86°C None found - (at on foot depth) Sumer 3 Metavolcanic and Main wam spring |Maximum re-Two closely located - Bay Wam alluvium about ane,2nd corded temp.{springs occur at edge of Springs spring @ 0.25 m |of spring was |a marsh just SE of Sumer (No fun-&warm ground ob-|35°C at a ph_|Bay lakearoles)served up to 40 mj of 7.0 ]o 5 )5 10 Km Sea 166¢30° a ey Et SSS Bering 1 Reese 57)Gay =Pear ereS hareoreDriftwoodpretreateeviasBay»%Table Top vve"¢ NORTH 4 Ve Min.Spot a Pt.Kadin H-5 3°45' Makushin Bay Portage 167° ' ALASKA Map Symbols aN (USA) Fault:dashed where approximate ce. e Fumarole field O Warm.and/or hat snrinns --§3°45" sor| as«0.,Makushin14,44"Volcanoeatervee ot otetotete! Makushin Bay Portage Bay a weraeeg pg aA MYfataatAap,o_o. - ALASKA (USA)Map Symbols aN Fault:dashed where approximate D Fumarole field Warm.and/or hot springs Recent volcanic vent bCalderaoof \-Map location (Northern part ofUnalteredvolcanicrocksUnalaskaIsland) Plutonic rocks Unalaska Formation FIGURE 1.Simplified geologic reconnaissance map of ; the northern part of Unalaska Island. July 24,1980 FIGURE 2.The main part of fumarole field.no.1 as viewed lookinganortheasterndirection. February 27,1982 FIGURE 3a.Makushin Volcano as viewed looking in a west-northwestern direction.Fumarole field no.2 dominates the bottom center of the photograph as outlined by the thaw region.Photograph was taken three days after a fresh snow.A steam cloud near the summit of Makushin Volcano marks the location of fumarole field no.6. 1980August8 iningieldno.2 as viewed 100kinpartoffumarolef«The maFIGURE3b TON.a northwestern direct i mieTk a * a wha,*" a =Se reaakfoBEAugust 11,1980 FIGURE 4.Part of fumarole field no.3 as viewed looking in a northwest direction.Photograph by Kirk E.Swanson. August 8,1980 "FIGURE 5.Part of fumarol field no.4 as viewed looking in an eastern :direction. August 12,1980 FIGURE 6.Fumarole field no.5 as viewed in a western direction. August 11,1980 thwesternInanorFumarolefieldno.6 as viewed direction. FIGURE 7. oatt. -_We =:%*3 3Tah xDtaa 1968 Fumarole field no.7 as viewed looking in a westernFIGURE8.Photograph by William E.Long.direction. Sugarloaf Cone Fumarole Field No.'\ hi Biizhas3 Ma rare 1981>August 12 viewed through Photograph by Mark J.Id no.8 and Sugarloaf Cone as fog in an east Fumarole fie Larsen. FIGURE 9a..-northweastern direction. July 23,1980 View of an old cairn that marks the location of fumarole field no.8. FIGURE 9b. Summer Bay Warm Spring. Well No.1 at Summer Bay. Well No.2 at Summer Bay. Hot Spring near Fumarole Fleld No.1. Hot Spring near Fumarole Fleald No.2. Hot Spring near Fumarole No.3. Hot Spring near Fumarole No.3 (Different spring elite); Cl FIGURE 10.Diagram showing the ratios of major ions of hot-spring waters from Unalaska Island and of hot waters from two exploration wells near Summer Bay on Unalaska Island.Data from Motyka et al.,1981,and from author. wyme28.O7,03 ,glabe GEOLOGICAL AND ENGINEERING STUDIES FOR GEOTHERMAL DEVELOPMENT ON UNALASKA ISLAND John W.Reeder,Ph.D.*,Michael J.Economides,Ph.D.**,and Donald R.Markle****State of Alaska Division of Geological and Geophysical Surveys : , **University of Alaska,and**k*State of Alaska Division of Energy and Power Development,U.S.A. Summary Geothermal resource investigations on Unalaska Island have focused on the,'Makushin Volcano and the Summer Bay regions,12 km and 3 km respectively from the' 'community of Unalaska.In total,8 fumarole fields have been located in the Makushin Volcano region.Large hydrothermal reservoirs,having temperatures in excess of: :150°C and extendingto depths of about 2 km,are suspected to exist in the region 'marked by the fumarole fields on the southeast flank of Makuskin Volcano.The loca- tion of these southeast flanking fumarole fields are controlled by plutonic-metavol- -canic boundaries and corresponding fractures,as well as by large northwest oriented fracture systems that are interpreted to have been caused by tectonic stresses.'i. } -In this paper geological and engineering considerations with respect to any poten-. tial geothermal development in the Makushin Volcano region are presented.A plan for,. further exploration and exploratory drilling is also included. ° 1.Lis KRULL Lun Unalaska Island is art of the Aleutian Island i »The Makushin Volcano on Unalaska Island is one __at least 36 volcanoes on this land arc which have been re- ported active since 1760 (Ref.1).Such volcanic regions,with shallow magma bodies and deep tectonic fracture systems,represent a favorable setting for the existence of large hydrothermal reservoirs. During volcano investigations in the Aleutian Islands,Drewes et al.(Ref.2) observed fumaroles and hot springs on the top and on the south flank of Makushin Vol- cano.Later,Miller and Smith (Ref.3)suggested that a high-level magma chamber exists under the summit caldera of this volcano.During more recent geologic investi- gations of Unalaska Island,Reeder (Refs.4 and 5)discovered active fumarole and hot-spring fields on the flanks of Makushin Volcano.Many of these fumarole fields are probably the surface expressions of vapor-dominated hydrothermal systems. The Unalaska community presently serves the largest American fishing fleet for 'the:Bering and North Pacific region and it could play a major role in the development.of a bottomfish industry.In addition there is nearby potential for outer continental|shelf oil,gas,and mineral production.Present peak electric utility demands for|:Unalaska is 15 MW,including both the publicly owned diesel generators and those| operated by the private fish processors.Projections for future energy demands are| risky,but peak demands by the year 2000 could reach between 30-60 MW in response to. expanding:resource industries. While a sizeable portion of the island population appears to be "prodevelopment,”- there are prominent forces that are apprehensive.Apart from any development,Unalaska needs to develop an inexpensive and reliable supply of energy.Geothermal resources| 'can play an important part in Unalaska's energy picture,and could be the key to: total energy self-sufficiency.; _2.FUMAROLE FIELDS A total of eight fumarole fields were examined by Reeder (Refs.4 and 5)in the Makushin Volcano region during the summers of 1980 and 1981.They were arbitrarily . numbered for identification purposes in a clockwise direction.The location of these.fumarole fields-are shown in Figs.1 and 5.: The Unalaska fumarole fields vary in character and dimension.Fumarole field,no.1 consists of fumarolic activity (i.e.,at boiling point),of warm ground,and of -outcrops of highly hydrothermally altered plutonic and metavolcanic rocks covering.'approximately a 120 m by 60 m region as shown in Fig.2.Field no.2 has fumarolic.'activity and warm ground covering a region about 1 km long and up to 400 m wide as shown in Fig.3.Fig.3 also shows a region consisting of outcrops of highly hydrothermally altered plutonic and metavolcanic rocks.Like field no.2,field no.3 consists of fumarolic activity and warm ground covering a region about 500 m long©and about 450 m wide;a region also consisting of outcrops of highly hydrothermally-'altered plutonic and metavolvanic rocks.Field no.4 consist of fumarolic activity:covering a narrow region only about 60 m long,located along a stream and a lateral. moraine.Superheated fumarolic activity and warm ground covering a 90 m by 90 miregionofunalteredvolcanicbecciaoccursatfieldno.5.Field no.6 is a fairly;large steam vent on the top of Makushin Volcano.It occurs as shown in Fig.4 mainly;in a 100 m diameter region near a small dome of unknown composition and within the}remains of a small cinder cone partly covered with sulphur deposits.This field is:found in the 3 km diameter ice-filled summit caldera of Makushin Volcano.Field no.°7 consists of minor activity located in a glacial till.Field no.8 consists of ©minor fumarolic activity and hot rock positioned on top of a small knob located just| west of the Sugarloaf Cone,which is a region of unaltered basalts that have retained their constructional forms. Warm and hot water springs were found at lower elevations as shown in Fig.5.Initial water analyses of some of these hot and warm springs were done by Motyka et al. (Refs.6 and 7).Their results indicated near neutral sodiun/bicarbonate/sulphate waters that were similar in chemical character to hydrothermal waters described by Mahon et al.(Ref.8).°the systems described by Mahon,any of the hot spring waters consist predominantly of meteoric waters which have bee..heated by vapor dominated hydrothermal systems generated from greater than 150°C alkali-chloride waters at greater depth.Because the level of the ionic composition in the fluids are different for springs near different fumarole fields,the Makushin water analyses indicate thepossibilitythatseveralseparatehydrothermalsystemsexistintheregion. 3.GEOLOGIC SETTING The rocks of Unalaska Island include an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewes et al.(Ref.2},a group of plutonic rocks intermediate in age,and a younger group of unaltered volcanic rocks. The rocks of the Unalaska Formation have been altered under conditions of the zeolite and/or lower greenschist facies.Perfit and Lawrence (Ref.9)argued that these: rocks occurred mainly during the emplacement of the plutonic bodies.The region to the southeast of Makushin Volcano consists mainly of rock exposures of the Unalaska Forma- tion whereas unaltered volcanics make up the Makushin Volcano and most of the rock: exposures to.the northwest as shown in Fig.l. The Unalaska Formation in the region of fumarole fields no.1,no.2,and no.3 has been extensively intruded by plutonic bodies of gabbro and intermediate plutonic.rocks.The intrusive bodies and the surrounding Unalaska Formation are extensively fractured especially along contact boundaries.The fractures serve as conduits for any hydrothermal convection at least near the ground surface.For example,a plutonic. body occupies the region between fields no.1 and no.2,where the hydrothermal surface|manifestations of fumarole fields no.1 and no.2 are oriented in a general northeast|direction along the northern and southern boundaries of this plutonic body respectively.! One prominent near vertical fracture on the northern boundary of this pluton strikes east-west directly through fumarole field no.l. Several near vertical fractures,striking between N 40°W and N 70°W and appearing -to be normal faults,were found near the vicinity of the fumarole fields as shown in Fig.1.Two of these faults,which strike about N 60°W and bound the field no.2, 'extend nearly the entire length of the northern part of Unalaska Island;a distance :of over 36 km.These fractures are active since they disrupt soil horizons. The underthrusting of the Pacific plate under the North American plate causes| compressional stresses in the direction of plate convergeace in the are region as_ indicated by Nakamura (Ref.10).Because the motion of convergence of the PacificandNorthAmericanplatesatUnalaskaisapproximatelyinaN45°W direction,these | near vertical northwest striking fractures are suspected to have been caused by compressional tectonic stresses.The fractures,even though they correlate with most of the fumarole fields,do not appear to influence the actual surface configuration|of the hydrothermal manifestations.Thus,these fractures do not appear to serve as conduits near the ground surface for hydrothermal convection. For Makushin Volcano,Nakamura et al.(Ref.11)determined,based on the orienta-'tion of flank eruptions,a maximum stress orientation of N 60°W where the expected. azimuth should be about N 45°W.If the expected azimuth is the actual one,then the recognized fractures striking about N 60°W should contain a strike-slip component.As shown in Fig.1,one N 60°W striking fault in the community of Unalaska was found| to have such a strike-slip component as based on observed slickensides. It is suspected that large hydrothermal convective systems exist in a northeastorientedzoneasroughlymarkedbyfieldsno.1,no.2,no.3,and no.4.Recent -lava flows (i.e.,flows that still retain details of their constructional forms)can be found northwest of this zoné as represented by the flows from the upper reaches of . Makushin Volcano and from the prominent rift zone near Point Kadin,northeast of this zone as represented by the flows surrounding the Sugarloaf Cone,and southwest of this zone as represented by the volcanic rocks of the Pakushin Cone.Yet,no recent volcanic extrusions have occurred within this northeast oriented zone nor from the region to the southeast.In fact no unaltered volcanic rocks have been recognized as' being extruded IYTOM CMNLS ZONE,LNALCALiNg Liide PLUDAOLY LU GaZse taccusauus awe "cus red in this region for the last three million years as based on the known range of. radiometricage dates f unaltered volcanics describe y Cameron and Stone (Ref.12).Such magma extrusiv...have not occurred either bev.u se the magma does not existatdepthorbecausemagmaexistatlargedepthswhereitmightbemoreviscousthan any wagmas to the northeast or to the southwest.If such magma bodies exist in the region,they might have a dike-like configuration oriented in a direction corresponding to the N 60°W fractures shown in Fig.1.°Such deep magma bodies as well as any shallow magma bodies located near the volcanic centers to the west,northwest,and north. could be the heat sources for large hydrothermal convective systems, In contrast,any hydrothermal convective systems linked to fumarole fields No.: 5,no.6,no.7,and no.8 are suspected to be limited to shallow zones where any heat sources would also be at shallow depths.Such shallow heat sources might be duetotheexistenceofrecentsurfacevolcanicflowsthatstillcontainheatassuspected at fumarole field no.8.Such shallow heat sources also might be due to the cooling of shallow magma bodies as reflected by the dome in field no.6. Most of the recent extrusive rocks (i.e.,volcanic rocks that still show their-surface constructional form)in the northern part of Unalaska Island are porous basalt--ic rocks.Any heat contained in such.rocks have been mostly removed,except for|small isolated areas such as the one found at field no.8.Hydrothermal convectivesystemsmightexistinthefracturedUnalaskaFormationandcorrespondingplutonic°bodies which are suspected to underlie most of the unaltered volcanic rocks of the:northern part of Unalaska Island.As of yet,no real evidence has been found for the. existence of such systems.In fact no hydrothermal systems are known to exist in the.Unalaska Formation beyond the immediate fumarole field regions of the Makushin Volcano. except at Summer Bay near the community of Unalaska as shown in Figure 1.This: particular system as documented by Reeder (Ref.13)does not at present show any sub-. stantial promise for geothermal utilization beyond a direct-use type of development. The geothermal anomaly on the southeast flank of Makushin Volcano might not be_ unique for the Aleutian arc.For example,the rock groups found on Unalaska Island. Islands;i.e.,an early series consisting of a marine volcanic and sedimentary sequence "can be correlated with rock groups found throughout the eastern and central Aleutian© that has been metamorphased to a greenschist grade,a middle series of plutonic rocks,: and a late series consisting of an unaltered sequence of late Tertiary subaerial vol- canic and sedimentary rocks as described by Marlow et al.(Ref..14).In addition, the Quaternary calc alkaline magmatism found on Unalaska Island is similar to mag- matism found within the central sections of four major are segments as recognized by Ray et al.(Ref.15)which make up a good part of the Aleutian arc.The large frac- ture systems caused by the convergence of the Pacific -North American plates would also be expected near the Quaternary volcanic centers throughout the Aleutian arc, where such fractures should have strikes similar to the direction of maximum horizon-.tal compressionas determined by Nakumura (Ref.11). 4.PLAN OF ACTION A northeast oriented zone roughly marked by fields no.1,no.2,no.3,and no.4 has been identified as possibly containing substantial hydrothermal reservoirs.+Although further exploration may better define the nature of such reservoirs in the.Makushin Volcano region,deep exploratory drilling along with appropriate well testing :such as described by Economides et al.(Ref.16)will be required to make any estimates; of the nature and the development potential of such geothermal reservoirs.It is:' recommended that geothermal drilling with the capability of reaching depths of 2 ka |be considered in this northeast target zone. If any deep geothermal drilling is to be undertaken in the Makushin Volcano | region,an access road would be required to the drill site from the coast.With' respect to the northeast oriented target zone,there are only three potential road approaches:.the Glacier Valley,the Makushin Valley,and the Driftwood Valley asshowninFig.5.Of these,the Glacial Valley and the Makushin Valley approaches would require,especially in the upper reaches of the Makushin Valley,the routing of .the road across large rivers and through fairly deep'canyons.in ¢ofifras€,a 8664 'part of the 16 km Driftwood route as shown in Fig.5 would be at higher elevations,|avoiding canyons and ma drainages.In this route,c bridge would be required at-point A and.extensive veurock blasting would be requii:cd at point B (Fig.5).An existing road does connect Driftwood Bay with Sugarloaf Cone.However,this road is washed out at numerous places and considerable repairs would be necessary to make it passible.An abandoned airstrip,1100 m by 35 m,is located at Driftwood Bay as shown in Figs.5 and 6.It is expected that this airfield would serve as the logistical base.for any planned drilling.The surface of the airstrip is currently in poor condition but.it can be upgraded to receive heavy traffic in a short period of time.The cost for building the proposed road to site C and for rebuilding the airstrip at Driftwood| Bay should be under 2 million U.S.dollars,Table 1. Once entering the northwest oriented target zone at site C,any further road|'construction would require extensive rock removal and major bridge constructions. Further surface exploration could be conducted to determine drilling targets,but logistical constraints may limit the drilling target to site C.Directional drilling from this site could greatly extend the target region.Site C is located at an eleva- falls at any time of the year. The main emphasis suggested here for further exploration is deep drilling.Such tion of about 600 meters above sea level,a site that would be engulfed a good part of.the time by the famous Aleutian fog and could experience strong winds and snow: a recommendation should not be considered unusual especially when considering the: Aleutian weather conditions and due to the remoteness and ruggedness of the terrain. 'Such a recommendation is also consistent with the general exploration and reservoir 'assessment plan suggested by Reeder et al.(Ref.17)for site-specific investigations| in Alaska. Emphasis on deep drilling should not rule out other exploratory surveys conduct-' 'difficulty and expenses involved in undertaking standard exploration surveys due to: ed priorto and/or during deep exploratory drilling.For example,if shallow drill-holes (i.e.,less than 200 meters in depth)could be drilled by helicopter support,:'they would be of value in obtaining temperature gradients and even rock permeability© 'values for the Unalaska Formation and the plutonic bodies found in the region south-east of Makushin Volcano.Low temperature gradients and high permeability values .would be expected for most of the unaltered volcanics on Unalaska Island,thus shallow, exploratory drilling in these bodies would not be recommended.; In addition,resistivity and gravity surveys would be highly recommended prior to: drilling.These surveys would be geared toward defining the extent of the Unalaska-Formation and any hydrothermal reservoirs present.Passive seismic surveys which -should be conducted over a long period of time (i.e.,at least several months)could; -be very helpful in recognizing any magma bodies and/or reservoir.During the drilling. operation,a portable seismograph should be operated near the drilling operation because of volcanic hazards. 5.DEVELOPMENT ECONOMICS Geothermal energy is "location intensive".Hence unlike fossil fuels,there isaneedforthebenefitedmarkettobeincloseproximitywiththeresource.Unalaska Island,with its relatively sizeable population and a large fishing and processing-'industry presents an attractive target for geothermal development.A report by the.U.S.Bureau of Land Management (Ref.18)projects an electric utility demand of 50 NW by the year 2000 under a base case.Anticipated offshore petroleum exploration in the Bering sea will increase the demand.The same B.L.M.report projects a demand of 56 MW if moderate oil and gas leasing in the outer continental shelf proves successful. Their projections appear on Fig.7. The present economy of the island is dependent on its harbor and the associated fishing and processing operations.More than 15 plants are located on the island, processing a variety of seafoods,dominated by king crab and salmon.In 1978 Dutch Ugrhar (lTinalaska)was rated ag the nymber one port by the National Marine Fisheries Service on the basis OF UNE VALUE OL Line SEaLUUU Laukuce -The 1980 employmen 1 Unalaska was 1600 "average ual full time jobs”.This-figure is the result of u..extremely non-homogeneous emp..,ment picture with a peak of 6000 laborers during the fishing season.The B.L.M.report projects a total employment of 9000 by the year 2000 with moderate oil and gas development. At this time electric power is generated by the city and by each of the private processors.However,consolidation is likely if an attractive single power source (suchasgeothermal)becomes available. Table 1 presents a best estimate capital investment scenario for a 30 MW geothermalpowerplantonUnalaskaIsland.Such a geothermal power development would require a 36 km service road from Unalaska and possibly 16 more kms of road connecting the site with the abandoned military airstrip at Driftwood Bay.A similar calculation was done by Economides et al.(Ref.19)for a variety of plant sizes in increments of 10 MW. Because any new energy venture needs to be measured against existing or other:'possible options,a comparison between geothermal and diesel power plants of same©Maximum output sizes is presented in Fig.8.While geothermal.power plants of less|'than 30 MW appears less attractive when compared with diesel generators,they rapidly 'become desirable at larger plant sizes.Taking into account the Bureau of Land Manage- :ment extimate of a 50 MW demand by the year.2000,geothermal development on Unalaska: appears feasible.The picture becomes even brighter when one contemplates future prices'for petroleum fuels.The analysis presented by Economides et al.(Ref.19)presumed a price for diesel that would remain constant in relation to 1981 U.S.dollars.This is 'however,highly optimistic,a fact that makes geothermal energy development 1more attrac--'tive. 6.CONCLUSION Any geothermal resources under the southeast flanks of Makushin Volcano on Unalaska |:'Island might to be of the sizes and types that could be developed for electrical energy'production.Such energy development appears to be economically attractive if the elec-. 'tric utility needs of the island exceed 30 MW. The design.of any output power plant must follow the resource evaluation and the :'projection of future needs.The former point addresses the need for deep exploratory.'drilling within the geothermal resource area in order to define the potenial of the: 'reservoirs.The latter point touches on significant social and economic considerations that need to be addressed by the local residents,and by the local and state govern- ments. 7.REFERENCES 4,Coats,R.R.:"Volcanic activity in the Aleutian Arc".U.S.Geological Survey, 2.,Drewes,H.,Fraser,G.D.,Snyder,G.L.,Barnett,H.G.,Jr.:"Geology of Unalaska.Island and adjacent insular shelf,Aleutian Islands,Alaska”.U.S.Geological,Survey,Bull.1028-S,1961,pp.583-676. 3.Miller,T.P.,and Smith,R.L.-:"Geothermal potential of high-level magma chambers|;in Alaska".In:Programs and Abstracts,The Relationship of Plate Tectonics to; Alaskan Geology and Resources Symposium (Anchorage,Alaska,U.S.A.:April 4-6,1977),Alaska Geological Society,1977,p.56. 4,Reeder,J.W.:"Vapor-dominated hydrothermal manifestations on Unalaska Island,and their geologic and tectonic setting”.In:Abstracts,1981 IAVCEI Symposium -.Are Volcanism (Tokyo and Hakone,Japan:Aug.28-Sept.9,1981),The Volcanolog-- ical Society of Japan and the International Association of Volcanology andChectetryoftheEarth's Interior.1981.pp.279-298. 10, W. 12, "13, 14, 15. 16. 17. 18, Reeder,J.W.:"Hydrothermal manifestations on Unalaska Island”.Alaska Division of Geological and ophysical Surveys,Open File [ort,In press. Motyka,R.J.,Moorman,M.A.,Liss,S.A.:"Assessment of thermal spring sites, Aleutian arc,Atka Island to Becherof Lake -Preliminary results and evaluation". Alaska Division of Geological and Geophsysical Surveys,Open File Report,In presse * . ° . Motyka,R.J.,and Moorman,M.A.:"Reconnaissance of thermal spring sites in the Aleutian arc,Atka Island to Becherof Lake".In:Transactions,Geothermal Re- source Council 1981 Annual Meeting (Houston,Texas,U.S.A.:Oct.25-29,1981), Davis,California,U.S.A.,Geothermal Resource Council,v.5,1981,pp.111-114. Mahon,W.A.,Klyen,L.E.,and Rhode,M.:"Neutral sodium/bicarbonate/sulphate hot waters in geothermal system".Chinetsa,v.17,no.l (ser.no.64),1980,pp. 11-23. 'Perfect,M.R.,and Lawrence,J.R.:"Oxygen isotopic evidence for meteoric water interaction with the Captains Bay pluton,Aleutian Islands".Earth and Planetary Science Letters,v.45,1979,pp 16-22. Nakamura,K.:"Volcanoes as possible indicators of tectonic stress orientation--- principle and proposal".Journal Volcanology and Geothermal Research,v.2, 1977,pp.1-16. Nakamura,K.,Jacob,K.H.,and Davies,J.N.:"Volcanoes as possible indicators of tectonic stress orientation-Aleutians and Alaska”.Pageoph,v.15,1977,pp.: 87-112., Cameron,C.P.,and Stone,D.B.:"Outline geology of the Aleutian Islands with paleomagnetic data from Shenya and Adak islands”.University of Alagka Geophys- ical Institute,UAG R-213,1970,152 pp. Reeder,J.W.:"Initial assessment of the hydrothermal resources of the Summer Bay region on Unalaska Island,Alaska".In:Transactions,Geothermal Resource Coun- cil 1981 Annual Meeting (Houston,Texas,U.S.A.:Oct.25-29,1981),Davis, California,U.S.A.,Geothermal Resources Council,v.5,1981,pp.123-126. Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,7.R.:"Tectonic history of the central Aleutian arc”.Geological Society America,v.84,1973,pp. 1555-1574. Kay,S.M.,Kay,R.«W.,and Citron,G.P.:"Tectonic controls of Aleutian arc tholeitic and calc-alkaline magmatism”.In:Abstracts,1981 IAVCEL Symposium Arc Volcanism (Tokyo and Hakone,Japan:Aug.28 -Sept.9,1981),The Volcano- logical Society of Japan and the International Association of Volcanology andChemistryoftheEarth's Interior,1981,p.171. Economides,M.J.,Ogbe,D.O.,Miller,F.G.,and Ramey,H.J.,Jr.:"Geothermal steam well testing".In:55th Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME (Dallas,Texas,U.S.A.:Sept. 21-24,1980),SPE of AIME,SPE 9272,1980,15 pp. Reeder,J.W.,Motyka,R.J.and Wiltse,M.A.:"The State of Alaska geothermal pro- gram".In:Transactions,Geothermal Resource Council 1980 Annual Meeting (Salt Lake City,Utah,U.S.A.:Sept.9-11,1980),Davis,California,U.S.A.,Geothermal Resource Council,v.4,1980,pp.823-826.. United States Bureau of Land Management:"St.George Basin Petroleum Develop- ment Scenarios Local Socioeconomic Systems Analysis”.OCS Technical Report no. 59.,1981. 19.Economides,M.J.,Reeder,J.,and Markle,D.:"Unalaska geothermal development”. In:Proceedings,"'d Annual New Zealand Geothe --1 Workshop (Auckland,NewZealand:Nov.9-11.981),University of Auckland ¢the New Zealand Ministry ofWorks,1981,pp.7-12.- Table 1.Capital Investment for a 30 MW Geothermal Power Plant,Unalaska Island ITEM °NUMBER Well 6 Piping - Road from 'Driftwood - 'Generator 1 'Transformer Station 1 _Transmission 'Line Road along Transmission line Contingency "Total to be depreciated DESCRIPTION 2,500 m,20 em diameter (assumed 50%dry wells) 1 km,20 cm diameter pipe,installed 16 km of service road,5.5 m wide,gravel, $125,000/km . 55 MW maximum capacity generator,installed 55 MW at $30/kW,installed 18 km of transmission line overland (helicopter installed),8 km underwater,$62,000/km 26 km of 5.5 m wide gravel road,$125,000/km Subtotal 10%of capital COST $12,000,000 250,000 , $2,000,000. $20,000,000: $1,375,000: $1,612,000: .$3,250,000: $40,485,000| $4,048,700 $44,535,700- 1 5 -i°)5 10 Km s Bering "\Reese 5% :Driftwood -8 °F |Tobie Top:YC Mtn.Cy" -§3°45°F Makushin 8ay 4 Portage Bay we pe pte.oN tr | ea 166°30° §4°- "2 Unolaska : ge Bay Cone B oy Map Symbols .o>---Fault:dashed where approximate Fumarole field Warm and/or hot springs Recent volcanic vent e Oo * AAS)Caldera Unaltered volcanic rocks Plutonic rocks Unalaska Formation ALASKA: (USA) &a(Ff \-Map location :(Northern part of Unataska Island) Figure 1.Generalized geologic map of the northern part of Unalaska Island. Figure 2. oe gi 3 ran A O99Lee”"ed«xoroAPy.ihe xseneSanneyeetee hege©ee ak SAM,Even,POE The main part of.fumarole field no.:1 as viewed looking in a northeastern-:direction.Photograph by John W.Reeder,1980.:of,ae eo ceeeeeeSteelpeereheggoe Figure 3.The main part of fumarole field no.2 as viewed looking in a southwestern direction.Photograph by John W.Reeder,1981,: zwas:Megha et =PorenginearteSoFigure 4.Fumarole field no.6 as viewed from the air looking in a northwestern direction.Photogravh by John W.Reeder.1980.' . 22&°o ¢ al 'xr fo3w- -»2< =2 -2%96- VUo°c= °o °teeof€E-3 badww = e ' 8 e.>we o 3: BN3PBS , oohiULES POWAV showing the location ofregionapoftheMakushinVolcano le fields,hot and/or re 5.Topographic m drilling site 'Figu and a proposed deep exploratorySprings,warmfumaro Ss road,-and acce 1 epee eettaWVaaee,' ° '.Paty eS ie .+,STEA LIOE®thon nt ml pe:a :ree eta na wae Se -s .ae ae from *:: the Bering Sea...Photograph by Michael J.Economides and John W..Reeder,=|:"yp1981.re Los,a rertf4ut'bigs:Sota!« ;"rz ;Figure 6.View of the Driftwood Bay airstrip taken during a landing.approach nas 60 F- BLM(Mean scenario)aco)|io)[o)|"--BLM(Base case)Powerdemand(MW).S|10 9 LL |||| 1980 1985 1990 1995 2000 Year Figure 7.Electric utility demand for Unalaska Island from a BLM report (Ref.18). Rateofreturn(%)20 +" _ / | / "/ -/ 2 /10 0 ..+7 ----Geothermal power plant -Diesel power plant 0 rTTTyprrrrTy rrr ry rrr rye rrr pr rr101520253035 4 Plant capacity (MW) Figure 8.Comparative economics for geothermal and diesel power plants on UnalaskaIsland(Ref.19).; 35.97.oS THE GEOLOGY AND GEOTHERMAL RESOURCE OF THE MAKUSHIN VOLCANO REGION OF UNALASKA ISLAND,ALASKA John W.Reeder?),David Denig-Chakroff(2),and Michael J.Economides (3) (1)Alaska Division of Geological and Geophysical Surveys,Pouch 7-028,Anchorage, Alaska 99510,U.S.A.(2)Alaska Power Authority,334 West 5th Ave.,Anchorage,Alaska 99501,U.S.A.(3)Dowell-Schlumberger,Marble Arch House,66/68 Seymour St.,London WLH5AF,U.K. ABSTRACT Geological,geophysical,geochemical,andwellflow-test data suggest a 13+km™and a Slightly less than 193°C water-dominated reservoirbeneaththeMakushinVolcanocalderathatreaches a depth of about 4.4+km.Through numerousfractures,this reservoir is presently discharging on the northern,eastern,and southern flanks of the volcano as reflected by numerous fumaroles. Rising gases are also escaping directly to thesurfacethroughthecalderaasreflectedbythe largest fumarole on the summit caldera. INTRODUCTION The Makushin Volcano region of Unalaska Island,which is located in the eastern part of the Aleutian Islands,has been the site of a State of Alaska geothermal exploration program. Following extensive geological,geophysical,and geochemical investigations of the region,a 593mexploratorywellwasdrilledbyRepublicGeothermal,Inc.This well encountered a 192.8°C water-domi nated reservoir that has a 2.04 to 2.17(kg/hr)}/(N/m°)}productivity index (Economides andothers,1985).A very large water-dominated geothermal reservoir exists in the Makushin Volcano region. The objective of this paper is to develop a geothermal model for the Makushin Volcano region.This model will be based on geology,which in addition to general geology will includegeothermalsurfacemanifestations,faults,welltests,gravity,and whole-rock geochemistry. GEOLOGIC SETTING The Aleutian arc is part of a ridge-trench system associated with active volcanism and seismicity.For the Unalaska Island region of this arc,the Aleutian trench is located about 180 km to the south.The floor of the Pacific Ocean (Pacific Plate)approaches the Aleutian arc (NorthAmericanPlate)in a NW direction at a rate of about 7 cm/yr (Minster and others,1974)where the Pacific Plate is being subducted under the North American Plate at the Aleutian trench. The rocks of Unalaska Istand include an older group of altered sedimentary and volcanic rocksdesignatedtheUnalaskaFormationbyDrewesandothers(1961),a group of intermediate-ageplutonicrocksthathaveintrudedtheUnalaskaFormation,and a younger group of unalteredvolcanicrocks(fig.1).The region SE of Makushin Volcano consists mainly of rock exposures belonging to the Unalaska Formation,whereasunalteredvolcanicsmakeuptheMakushinVolcano and most of the rock exposures to the NW of a line extending from Pakushin Cone to Table TopMountain(fig.1). The Unalaska Formation is upper Oligocene tomiddleMiocene(30 to 15 mybp)as based on fossils (Lankford and Hill,1979;and Drewes and others, 1961).This formation in the N part of Unalaska Island consists of conglomerate and sandstone units,and of numerous volcanic lava and breccia flows with some suspected volcanic sills. The Unalaska Formation has been intruded by three plutons and several smaller intrusive bodies.Individual plutons are zoned from mafic margins to felsic interiors and show calc-alkalinechemicalcharacteristics(Perfit and others, 1980).Radiometric ages determined for two oftheseplutonsyieldedagesof11+mybp (Marlow andotnerss1973)and 13+mybp (Lankford and Hill,1979). The Makushin Volcano of Unalaska Island is one of at least 36 volcanoes on the Aleutian arc that have been active since 1760 (Coats,1950). The top of the volcano is dominated by a 2.4 km diameter caldera that erupted about 8,000 ybp(Reeder,1983).The most recent eruptions of Makushin Volcano occurred in 1938,1951,and 1980(?)as small flank eruptions with the 1938eventbeingthelargest(Simkin and others,1981). The unaltered volcanics unconformably blanket the Unalaska Formation as well as any intermediate age plutonics that have intruded it.Most of these unaltered volcanics are pre-Holocene and post-Pliocene,and have been derived mainly from the immediate Makushin Volcano region,Except for Pakushin Cone,Wide Bay Cone,and the Point Kadin cones,the volcanic cones of the area have Reeder and others 10 Km pering oe Driftwood NORTH Bishop Pt Pt.Kadin 2.Pakushin »” -*>,Cone: 53°45' Makushin Bay tec Top -2BANMINPANMS/ig wide Bay Cone | Sea 166°30° 54° Unalaska Bay Map Symbols Fumarole field Warm and/or hot springs Recent volcanic vent Caldera Unaltered volcanic rocks Plutonic rocks Unalaska Formation Fault:dashed where approximate aeoof\-Map location (Northern part of Unalaska Island) Figure 1.A simplified geologic map of the northern part of Unalaska Island,after Drewes and others(1961)and Reeder and others (1985c). Bouguer gravity profile in figure 2. undergone intense glacial erosion,which occurredbefore11,000 ybp (Black,1976).The Point Kadin cones as well as the Sugarloaf Cone occurred at about or shortly after the time of the Makushincalderaeruptionevent(Reeder and others,1985b). GEOTHERMAL SURFACE MANIFESTATIONS During regional geologic investigations of Unalaska Island during the summer of 1980, previously unreported active fumaroles and hot springs were discovered on the flanks of MakushinVolcano(Reeder,1982).Of the eight majorfumaroleareas(fig.1),only fumaroles no.3 and The A-A'line is the location of the complete no.5 (Drewes and others,1961)and fumarole no.6 (Maddren,1919)had previously been reported.Of these fumaroles,only the large plume'fromfumaroleno.6 can be seen from Unalaska,the only community on Unalaska Island. Some warm and hot springs exist in or atlowerelevationstothefumaroles.These springs are rich in HCO,,SO,,and Ca.They haveapparentlyoriginatedfrommeteoricwatersthat, after infiltration into fractured rock,have been heated by ascending gases and/or by conductionfrom,wall rock (Motyka and others,1983).The"He/"He compositions of these rising gases as. determined by Motyka and others indicate adefinitemagmaticinfluence.The fumarolicactivityisevidenceforatleastashallowvapor-dominated zone beneath each fumarole. "FAULTS Faults,mostly near vertical and having smalldisplacements,are found throughout the region.In a few cases,faults have been found trending directly into Quaternary volcano centers such asPakushinCone,Sugarloaf Cone,and even activeMakushinVolcano(Reeder and others,1985b).Thelocationofnearlyallofthefumarolesappeartobeatleastpartlycontrolledbyfaults(fig.1).For example,an EW striking fault and a N 50°Wstrikingfaulthavebeenrecognizedas'intersecting at fumarole no.1 (Reeder and others,1985c;and fig.1). Many of the fractures of the northern part of Unalaska Island reflect orientations expected for a regional stress caused by the subduction of the Pacific Plate,namely an approximately N 50°W striking set with approximate corresponding N 05°W,N 40°E,and N 85°E sets (Reeder,1985). Another observed N 68°W striking set has been explained by Reeder as being caused by the late Miocene rotation of the northern part of Unalaska Island.These fractures,before this rotation, would have had the expected N 50°W strike. WELL TESTS Three temperature gradient holes were drilled in 1982 to depths of 460 m on the Tower flanks of Makushin Volcano,and encountered temperatures of up to 195°C.These holes were drilled by Republic Geothermal,Inc.under the Alaska Power Authority contract.These holes and their temperature gradients are described by Isselhardt and others(1983a). In the summer of 1983,an exploratory wel]was drilled near fumarole no.1 (fig.1},a siteoriginallysuggestedbyReederandothers(1982). This well encountered a steam zone in fractured mafic crystalline rock (gabbro-norite)at 205 mdepthandthenencounteredawater-dominated zoneatalargefracture,also in mafic crystalline rock,at 593 m depth.These waters were moderately saline,low-bicarbonate waters at a temperature of 192.8°C and at a static bottomholepressureof3.4 x 10°N/m”gage. Several static temperature profiles of this well were obtained by Republic Geothermal,Inc. These surveys indicated that the well,which islocatedatabout360ma.s.1.(above sea level), has a steam zone with a vapor-liquid interface atadepthof250m(110 m a.s.1.).Below this depth is a liquid zone,which increases to a maximum temperature of 203.9°C at a 457 m depth,then declines slowly to a temperature of 201.7°C at thebottomofthehole.| A 34 day flow test was performed on this well as described by Campbell and Economides (1983)andEconomidesandothers(1985).Sustained flow Reeder and others through a 7.6 cm diameter well of 28,600 kg/hr wasachievedfor19aysofthistestwithTessthan6.9 x 10°N/m of pressure eirawdown from abottomholepressureof3.4 x 10°N/m”gage.The well productivity index that was obtained from thetestwas2.04 to 2.17 (kg/hr)/(N/m*).As based on a simple material balance calculation that assumes a constant total compressibility for the system,Economides and others (1985)estimated a reservoirmassofabout3.1 x 10°°+kg.For this detepmigation,a water compressibility of 4.351 x1049Mo/N and a rock compressibility of 8.702 x10m°/N were assumed.Such a reservoir wass would equate to a water volume of about 3.1 km”. GRAVITY A total of 155 gravity stations have beenobtainedforthenorthernpartofUnalaskaIsland (Reeder and others,1985a}.Figure 2 shows acompleteBouguergravityprofileacrossMakushinVolcano.Based on two-dimensional modeling,the dense (2.8 gm/cc)mafic crystalline rocks,whichareexposedjustSEofMakushinVolcano(fig.1),underlie the entire region (Reeder and others, 1985a;and fig.2).The only area where thisdenserockmightnotbecontinuouswouldbealongalinearNEorientedgravitylowthatpasses directly through the Makushin caldera.ThisgravityanomalyhasbeeninterpretedbyReederandothersasaNEorientedfracturezonewithinthe crystalline rocks that has been covered by Makushin volcanics. The most prominent gravity low occurs directly over the caldera of Makushin Volcano(fig.1).Such an anomaly is probably due to theveryporousnatureofthebodyof"broken-up"rockdebristhatfillsthecaldera.Such a geologic formation is the most likely,candidate in thisregionforcontianinga3+km?body of water. 'A DISTANCE (km)A'18 '14 '19 '8 '2 r140 COMPLETE BOUGUER Liz9 GRAVITY (Density 2.6) r (mgal) °Observed 100 nm 1 1 1 1 1 ,SN aa RESIDUALWAGRAVITYr-10 (mgal)ON «Calculated [-20 18 14 10 6 214i4Aii.1 i am 2.1 [2.5ee 25)pePrH2.3 (km) 2.8 2.8 r ml DENSITY MODEL (gm/cc) Figure 2.Gravity profiles and crustal density cross section for line A-A'of fig.1. Reeder and others The caldera may be modeled as a vertical cylinder with a conservative radius of 1.29 km. The caldera fill has been determined to have a bulk density between 2.0 and 2.2 gm/cc,and altered Makushin volcanics have been found to have an average density of about 2.62 gm/cc (Reeder andothers,1985a).If the average bulk density of the caldera fill is taken as 2.1 gm/cc,then the porosity of the fill would be about 20%if the actual rock density of the fill is 2.62 gm/cc. Because the vapor-liquid interface occurred at about a 110 m elevation a.s.1.at the exploratory well,then let's assume water saturation occurs also at this same elevation within the caldera. Then,the 1850 m a.s.1.Makushin caldera may be modeled as a 2.1 gm/cc cylinder to a depth of 1740m(110 m elev.)that is flanked by denser Makushin volcanics.Then the cylinder may be extended in depth at a 2.26 gm/cc bulk density for water Saturated fill. observed gravity profile,such a cylinder would need to be extended to a depth of 2.62 km below the initial water saturation elevation,which would be to a depth of 2.51 km b.s.1.(fig.2). In summary,the Makushin caldera has justbeenmodeledasa4.36 km vertical cylinder with a 1.29 km radius that is filled with fairly porousmaterial.If the bottom 2.62 km of this cylinder is actually saturated to 20%of volume with water, thgn the Makushin caldera would contain about 2.7km™of water within a 13.6 km'region.Thisvolumeofwaterisonlysjightlylessthanthecalculatedvolumeof3.1 km”as based on the well test. WHOLE-ROCK CHEMISTRY With respect to the nature of the resource, the characteristics of the heat source are important.Two generic types of geothermalresourceshaveingeneralbeenrecognizedbasedon the origin of heat that drives their convective circulation systems.These generic systems,inturn,correspond to high temperature (greater than200°C)versus moderate to Tow temperature resources.The classic major geothermal systems around the world,such as those at Wairakei,New Zealand;at The Geysers of California,U.S.A.3;and at Larderello,Italy are al}associated with less than 1 million year old igneous systems that consist of a high silicic magma such as rhyolite or dacite (McNitt,1970).By contrast,most other volcanic and/or plutonic igneous occurrences that do not consist of high silicic melts do not have associated high temperature hydrothermal systems. Rhyolitic and dacitic rocks are lacking for a majority of the 36 plus active volcanoes of theAleutianare(Coats,1962).Thus,these active volcanoes are most likely associated with low to: moderate temperature geothermal systems. Nevertheless,the larger andesitic volcanoes may be underlain by trapped magma that has risen from great depths.Such shallow magma bodies might serve as a significant heat source for largemoderatetemperaturegeothermalsystems. In order to obtain a fit with the The Makushin Volcano of Unalaska Island is typical of such large andesitic volcanoes.The Makushin volcanic field is dominantly a tholeiiticprovince(fig.3).The tholeiitic volcanoes of the Aleutian arc are large centers where magmas canmoreeasilyreachshallowdepthsunlikethe smaller calc-alkaline centers.Tectonicallycauseddeepfracturesandlargecrustalrotations as previously discussed under the fault section could help encourage the rapid rise of such magmas.OQnce such magmas reach shallow depths, they can undergo'shallow,closed systemdifferentation(Kay and others,1982).The: tholeiitic magmas show a Fe enrichment trend (fig.3),which is consistent with low-pressure and.high-temperature crystallization in a _largeshallowmagmabody. Part of the shallow magma body underneath Makushin Volcano has been violently extruded from the system as reflected by the existence of a Makushin caldera.Magma probably still remains beneath and around the caldera fill,and it is this magma that would be the principal drivingheatsourcefortheMakushingeothermalsystem.Based on the gravity model,such magma would bedeeperthan2.51 km b.s.1.immediately beneath thecalderabutcouldbeatshallowerelevations beneath its flanks. iL 4 re n n 1 1 rn 1 1 1 744 VOLCANOES r FeO"/MgO FeO"(total Fe as Fe0}/MgO ratio versus Si0,for Quaternary volcanic rocks ofthe°northern part of Unalaska Island as shown in figure 1.The calc-alkaline(CA)and tholeiite (TH)boundary lineisfromMiyashiro(1974).Data is from samples that were collected by Reeder and others (1985c). Figure 3. DISCUSSION A large water-dominated reservoir exists beneath the Makushin caldera at a depth of 1.74. km to 4.36+km beneath the summit.Rising gases from this hot water reservoir are presently escaping to the surface through the caldera fill as reflected by the largest fumarole near the summit of the volcano.Through the numerous fractures,this reservoir is also discharging fluids to the N,E,and S,as reflected by the numerous fumaroles on the N,E,and S flanks of the volcano (fig.1).Such fluids,as they slowlymovealongfractureswithinthedensemaficcrystallinerocksoftheregion,may slowly gain heat by conduction from wal]rock.For example, the highest static temperature observed in the exploratory well was 203.9°C,and yet the inflowing bottomhole fluids remained at a constant 192.8°C temperature.This exploratory well, possibly by means of the recognized E-W strikingfracture(fig.1),is in direct hydraulic connection to the Makushin geothermal reservoir. Nevertheless,the inflowing 192.8°C fluids have probably been heated by the massive crystalline rocks,and such fluids are probably slightly warmer than the main Makushin geothermalreservoir.Recharge might be occurring veryslowlyfromtheWflankofthevolcanoaswellas from the summit region. It is possible that large quantities of hot water may also be located beneath the flanks of the volcano,especially beneath its NE and SW flanks where gravity has suggested a fairly large NE striking rift zone.Indeed,fumaroles no.5 and no.7 are located directly over this zone,and they represent the presence of at least some fluids within this zone.Nevertheless,large quantities of andesitic and basaltic lava extrusions have occurred on both the S and N flanks of this volcano during the Holocene (Reederandothers,1985b).Such large quantities of lava extrusion have occurred with no indication of any large phreatomagmatic explosions,which would be expected if magma came into contact with large ground-water bodies. In contrast,over 0.21 km?of phreatomagmatic flow deposits have been recognized as originating directly from the Makushin caldera during its8,000 ybp eruptive activity (Reeder,1982;andReederandothers,1985b).This suggest that a caldera and a ground-water reservoir within the caldera might have existed before the large 8,000 -ybp phreatomagmatic eruption.If magma is everintroducedagainintotheMakushingeothermal 'reservoir,large phreatomagmatic eruptions would be expected.Such phreatomagmatic eruptions may represent the principal cause for caldera formation in the Aleutian arc. The Makushin geothermal reservoir has been suggested to be confined to a 3 km wide NE oriented fracture zone underneath fumaroles no.1, 2,and 3 (Isselhardt and others,1983b).Field observations (Reeder and others,1985c)andgravitymodeling(Reeder and others,1985a) indicate the lack of any such highly fractured NE Reeder and others striking zone.In addition,the flowing bottomhole fluid temperature in the exploration well near fumarole no.1 was 192.8°C.This temperature is lower than the measured static temperature of 201.7°C at that same depth.Thisphenomenon,coupled with an _observed =statictemperaturegradientreversalfroma203.9°C maximum,indicates that the reservoir proper is actually located some distance from the well and not just beneath it. CONCLUSION The most likely place for a large geothermalsystemasrepresentedbyabout3km”of water at slightly less than 192°C would be within the Makushin caldera at a depth of up to 4.4 km.Such hot water would discharge gases through thecalderafill,which is reflected by the largest fumarole near the top of the volcano.Hot waters would also slowly discharge along fractures,which is reflected by fumaroles on the N,E,and S flanks of the volcano. Although this is a very simplistic model and not one without flaws,it does appear to be theonlymodelthatfitsthelimitedamountofdata presently available.Most geothermal reservoirsintheworldthatareassociatedwithQuaternaryvolcanoesarewithincalderastructures(McNitt,1970).The Makushin geothermal reservoir appearstobeanotherthatshouldbeaddedtothelist. ACKNOWLEDGMENTS Special thanks is given to the people ofUnalaskafortheircontinuoussupportofall aspects of this investigation.In addition,veryspecialthanksisgiventoAbi&Jim Dickson, Kathy &Bob Grimnes,Nancy Gross,and the Currier family for their help in keeping Reeder,duringhismanyyearsofdifficultfieldwork,from getting lost in the famous Aleutian fog. REFERENCES Black,R.F.,1976.Geology of Umnak Island eastern Aleutians as related to the Aleuts, Arctic and Alpine Research,v.8(1),p.7-35. Campbell,D.A.,and Economides,M.J.1983.A summary of geothermal exploration and data from stratigraphic test well no.1,Makushin Volcano,Unalaska Island,Proceedings of the Ninth Workshop on Geothermal Reservoir Engineering,SGP-TR-74,Stanford University,Stanford,Ca.,p.167-174. Coats,R.R.,1950.Volcanic activity in theAleutianarc,U.S.Geological SurveyBulletin974-B,p.35-49. Coats,R.R.,1962.Magma type and crustal structure in the Aleutian arc,in The Crust of the Pacific Basin,G.A.MacDonald and H. Kuno,Editors,American Geophysical Union Monograph Number 6,p.92-109. Reeder and others Drewes,H.,Fraser,G.D., Barnett,H.F.,dJr.,1961.Geology of Unalaska Island and adjacent insular shelf, Aleutian Islands,Alaska,U.S.Geological Survey Bulletin 1028-S,p.583-676. Economides,M.J.,Morris,C.W.,and Campbell, D.A.,1985.Evaluation of the Makushin geothermal reservoir,Unalaska Island, Proceedings of the Tenth Workshop on Geothermal Reservoir Engineering,SGP-TR-84, Stanford University,Stanford,Ca.,in press. Isselhardt,C.F.,Matlick,J.S.,Parmentier,P.P., and Bamford,R.W.,1983a.Temperature gradient hole results from Makushin geothermal area,Unalaska Island,Alaska, Geothermal Resource Council Transactions,v. 7,p.95-98. Isselhardt,C.F.,Motyka,R.,Matlick,J.S., Parmentier,P.P.,and Huttrer,G.W.,1983. Geothermal resource model for the Makushin geothermal area,Unalaska Island,Alaska, Geothermal Resource Council Transactions,v. 7,p.99-102. Kay,S.M.,Kay,R.W.,and Citron,G.P.,1982.Tectonic controls on tholeiitic and calc-alkaline magmatism in the Aleutizn arc,Journal of Geophysical Research,v.87(B5), p.4051-4072. Lankford,S.M.and Hill,J.M.,1979.Stratigraphy and depositional environment of the Dutch Harbor Member of the Unalaska Formation, Unalaska,Alaska,U.S.Geological Survey Bulletin 1457-B,p.1-14. Maddren,A.G.,1919.Sulphur on Unalaska and Akun Islands and near Stepovak Bay,Alaska,U.S. Geological Survey Bulletin 692,P.283-298. Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,T.R.,1973.Tectonic history of thecentralAleutianarc,The Geological Society of America Bulletin,v.84,p.1555-1574. McNitt,J.R.,1970.The geologic environment ofgeothermalfieldsasaguidetoexploration,Proceedings of the United Nations SymposiumontheDevelopmentandUtilizationofGeothermalResources,Geothermics,Special Issue 2,v.1,p.24-31. Minster,J.B.,Jordan,T.H.,Molnar,P.,and Haines,E.,1974.Numerical modeling ofinstantaneousplatetectonics,Geophysical Journal of the Royal Astronomical Society,v. 36,p.541-575. Miyashiro,A.,1974.Volcanic rock series inislandarcsandactivecontinentalmargins, American Journal of Science,v.274,p. 321-355. Snyder,G.L.,and Motyka,R.J.,Moorman,M.A.,and Poreda,R.,1983. Progress report -Thermal fluid investigations of the Makushin geothermalarea,Alaska Div.of Geol.&Geophys.Surveys Report of Investigations 83-15,52 pp. Perfit,M.R.,Brueckner,H.,Lawrence,J.R.,and Kay,R.W.,1980.Trace element and isotopic variations in a zoned pluton and associated rocks,Unalaska Island,Alaska:A model for fractionation in the Aleutian calc-alkaline suite,Contrib.Min.Pet.,v.73,p.69-87. Reeder,J.W.,1982.Hydrothermal resources of Makushin Volcano region of Unalaska Island, Alaska,in Circum-Pacific Energy and Mineral Resources Conference,3rd,S$.T.Watson, Editor,American Assoc.of Petroleum Geologist Circum-Pacific Series,p.441-450. Reeder,J.W.,1983.Preliminary dating of the caldera forming Holocene volcanic events for the eastern Aleutian Islands,The Geological Society of America 1983 Annual Meeting,Abstracts with Programs,v.15(6),p.668. Reeder,J.W.,1985.An analysis of fault and volcanic dike orientations for the Makushin Volcano region of the Aleutian arc,The Royal Society of New Zealand Bulletin,in press. Reeder,J.W.,Economides,M.J.,and Markle,D.R., 1982.Economic and engineering considerations for geothermal development in the Makushin Volcano region of Unalaska Island,Alaska,Geothermal Resource Council Transactions,v.6,p.385-388. Reeder,J.W.,Edge,D.B.,and Swanson,K.E.,1985(a).Complete Bouguer gravity map of the Makushin Volcano and Dutch Harbor region of Unalaska Island,Alaska,Alaska Div.of Geol. &Geophy.Surveys Report of Investigation,1 plate,in press. Reeder,J.W.,Swanson,D.E.,and Larsen,M.J., 1985(b).Unconsolidated deposits and geologically Recent volcanic rocks and faults of the Makushin Volcano and Dutch Harbor region,Unalaska Island,Alaska,Alaska Div. of Geol.&Geophy.Surveys Report of Investigation,1 plate,in press. Reeder,J.W.,Swanson,K.E.,Larsen,M.J.,and Edge,0.B.,1985(c).Geologic bedrock observation and map of the Makushin Volcano and Dutch Harbor Region,Unalaska Island, Alaska.Alaska Div.of Geol.&Geophy. Surveys Report of Investigations,2 plate,in press. Simkin,T.,Siebert,L.,McClelland,L.,Bridge, D.,Newhall,C.,and Latter,J.H.,1981. Volcanoes of the World,A Regional Directory, Gazetteer,and Chronology of Volcanism during the Last 10,000 Years,Smithsonian Institute, Hutchinson Ross Pub.Co.,Stroudsburg,Penn., 232 pp. s Ke ome ane)S DEVELOPMENT POTENTIAL OF THE MAKUSHIN GEOTHERMAL RESERVOIR OF UNALASKA ISLAND,ALASKA David Denig-Chakroff(!)John w.Reeder'2)michael J.Economides(3) (1)Alaska Power Authority,334 West Fifth Avenue,Anchorage,AK 99501, U.S.A. (2)Alaska Division of Geological and Geophysical Surveys,Pouch 7-028, Anchorage,AK 99510,U.S.A.(3)Dowell-Schlumberger,Marble Arch House,66/68 Seymour Street, London W1H5AF,U.K. ABSTRACT Flow tests and reservoir analyses haveconfirmedtheexistenceofa_productivegeothermalreservoirbeneathMakushinVolcanoon Unalaska Island in the Aleutian Chain.A prelim- inary economic analysis has been conducted todeterminethepotentialfordevelopingthe resource to meet the electric power demands of the Unalaska/Dutch Harbor community.The analy- sis was based on characteristics of the resource, deliverability of the reservoir,logistics of development and operation,and power market conditions at Unalaska.The analysis indicates that a geothermal power system may be econom- ically competitive with a diesel power system on the island.A detailed feasibility study of the project should be conducted which concentrates on electric load projections and market conditions at Unalaska. INTRODUCTION Unalaska Island is located in the Aleutian Archipelago about 800 miles southwest of Anch-orage,Alaska (Figure 1).The City of Unalaska, consisting of the adjacent communities of Unalaska and Dutch Harbor,is situated at the northern end of the island on a well-protected bay.Unalaska was an important crossroads for shipping and trade during Russian occupation(1741-1867)and during the Klondike and Nome gold rushes from 1897 to 1900.Its sheltered, deep-water port made Dutch Harbor a prime loca- tion for a major naval base during World War II. Since that time,the fishing and crabbing indus- tries have been the mainstay of Unalaska's economy. The Alaska Power Authority has recently completed a geothermal exploration program at Makushin Volcano near Unalaska and is involved in studies of both energy needs at Unalaska and alternatives for meeting those needs,including the geothermal alternative.The Alaska Power Authority is a state agency governed under execu- tive and legislative oversight by a seven-member board of directors appointed by the Governor of Alaska.Its goal is the orderly and economic development of energy resources to provide power at the Towest possible cost to the consumer and to encourage the long-term economic growth of the state. One objective of this paper is to summar- jze the final results of the Unalaska geothermal exploration program.A second objective is to present a preliminary economic analysis of utilizing geothermal resources, which were discovered in the vicinity of Makushin Volcano,to meet the current and future power needs of Unalaska.The'economic analysis has taken into account the charac- teristics of the resource,the deliverability of the reservoir,the logistics of development and operation,and the demand of the power market. vacces”UNALASKA ISLAND X ease came ©twcnasas onseio0 vocesFemSLOTASAEACSOUACEwe ™_ Figure 1.Map showing the location of the Unalaska geothermal project. THE RESOURCE AND THE RESERVOIR In 1981,the Alaska Legislature appropri-ated $5 million to the Alaska Power Authority for geothermal drilling and exploration at Makushin Volcano located 14 miles west of the Denig-Chakroff and others City of Unalaska (Figure 1).The appropriation was preceded by a number of geologic investigations that indicated potential for a significant resource at Makushin Volcano. A competitive request for proposals was issued in 1981 and,after evaluation of the responses,Republic Geothermal,Inc.,of Santa Fe Springs,California was selected by the Power Authority to plan and coordinate the exploration and drilling program.The program consisted of three phases.Phase I activities included data review and synthesis;technical planning;Jand status determination;permitting requirements; acquisition of baseline environmental data; geological,geochemical,and geophysical inves- tigations and mapping;and the drilling of three temperature gradient holes.Phase II activities included the drilling of a deep exploratory well and initial testing of the geothermal resource encountered.Phase III activities included continued and more extensive testing of thegeothermalresource,the drilling of a fourth temperature gradient hole,and an electrical resistivity survey to delineate the extent of the reservoir. Under Phase I,the first three temperature gradient holes were drilled in 1982 to depths of 1500 feet and encountered temperatures of up to383°F.Two of the holes indicated a close proximity to geothermal resources below,while the third appeared to be on the fringe of the geothermal system.The Phase I findings conciud- ed the strong probability of a water-dominated geothermal system in excess of 480°F on the eastern flank of Makushin Volcano at a depth of1983).4,000 feet (Republic Geothermal,Inc.,1983). Phase II of the exploration program was initiated in the Spring of 1983.The exploratory well was started in early June.The well encoun- tered a fracture at 1,946 to 1,949 feet that contained a substantial geothermal resource. Initial well tests confirmed a water-dominated geothermal system with a steam cap and with abottomholepressureof478psi(RepublicGeothermal,Inc.,1984a).The bottomhole flowing temperature was measured at 379°F;however,a static temperature of 395°F was measured at that depth.This temperature difference coupled with an observed static temperature gradient reversal from a maximum 399°F at 1500 feet indicates that the geothermal reservoir is located some distance from the well and communicates with the wellbore through a high conductivity fracture system(Economides and others,1985).The results of gravity and geologic investigations add substan- tial support to this conclusion (Reeder andothers,1985).The fluid from the producing horizon.is approximately 16%vapor and 84%liquid by mass at usable wellhead pressures.It mea- sures 7800 ppm total dissolved solids. Phase III of the project,conducted in 1984, consisted of further well testing and reservoir analysis,drilling a fourth temperature gradient hole,and conducting an electrical resistivity survey.The temperature gradient hole,drilled in an area that would be more accessible to development than the exploration wellsite,showed no indications of the exis- tence of a similar geothermal resource.The electrical resistivity survey revealed that the site of the current exploration well is ac- tually the most accessible site for encounter- ing the geothermal resource at a reasonable depth. Flow tests and reservoir analyses conduct- ed in 1984 confirmed a highly productivegeothermalreservoir(Economides and others,1985).Sustained flow of 63,000 Ib/hr was achieved through the three-inch diameter wellbore with less than two psi pressure drawdown from the initial 494 psi bottomhole pressure after 34 days.The productivity index derived from the flow test was in excess of 30,000 Ib/hr/psi,which indicates a phenomenal permeability-thickness product in the range of 500,000 to 1 million md-ft.Wellbore flow modeling indicated that a commercial -size wel] at the site should be capable of flow rates of 1.25 to 2 million lb/hr at a wellhead pressure of 60 psia.A material balance calculation byEconomidesandothers(1985)provided an estimate of reserves that could maintain this flow rate (capable of producing 7 to 12 MW ofelectricpower)for over 500 years. LOGISTICS OF DEVELOPMENT AND OPERATION The location of Unalaska in the Aleutian Islands creates difficulties for any capital project development.Although there are daily scheduled air freight and passenger flights and regularly scheduled barge service from Anchorage and Seattle,its distance from population centers may increase construction and operation expenses by a factor of 50%or more over continental U.S.costs. The Makushin geothermal exploration wellsite is located approximately 13 miles westoftheCityofUnalaskainaremote,rugged,roadiess terrain.Access to the site from the city requires crossing a three-mile wide bay, traversing the length of a seven-mile long, wetland valley,and contending with three miles of steep,rocky slopes and canyons.This location would clearly have a significant effect on the costs of both construction and operation of a power plant at the site and a transmission line to the City of Unalaska. In addition,weather conditions may be a serious impediment to development and opera- tion.Although the average annual temperature(38°F)at Unalaska is higher than many other regions of the state,heavy construction is generally limited to a four-month construction "window"due to wind and snow conditions.Even during summer months,when the average tempera- ture is around 50°F,high winds,heavy rains,and fog could impede construction,operation,and maintenance of a remote power facility. POWER DEMAND The power demand of the Unalaska/Dutch Harbor community has been marked by large fluc- tuations that follow the cyclical trend of the fish-processing industry.In 1978,Dutch Harbor was the nation's leading fishing port based on the value of its landed catch (Morrison-Knudsen Company,Inc.,1981).It has been estimated that the population of Unalaska Island has reached over 5,000 during peak fishing seasons.At such times,the peak power demand has reached 13+MW. However,over the past year,during a sertous slump in the fish-processing industry,the population has been estimated at about 2,000 and the peak demand has fallen as low as 4+MW. Unalaska is pursuing numerous options to diversify its economy,which could both increase and stabilize electrical loads.These options include developing additional marine support facilities,establishing a bottomfish industry, and increasing its tourist trade.In addition, the U.S.Coast Guard is considering the island as the site for a large search-and-rescue facility to respond to calls in the Bering Sea and North Pacific and the petroleum industry may use Dutch Harbor as a staging area for offshore oil development.Any one or combination of these ventures or a rejuvenation of the established fish-processing industry on the island could significantly change the power demand outlook at Unalaska over a very short period of time. The electric power demand on the island is met entirely with diesel powered generators.The city-owned electric utility primarily serves residential and small commercial users.The city has a current installed capacity of 3.9 MW and plans to increase its diesel generating capacity to 9.5 MW by 1987.Larger commercial establish- ments and industrial users generate power with their own diesel generators.They have expressed interest in tying into the city system once it has sufficient capacity to economically and dependably meet their demand. ECONOMIC ANALYSIS The analysis presented here is meant to pro- vide only a cursory look at the economics of developing a geothermal power facility on Unalaska Island.Prior to design and con- struction,a far more detailed feasibility study would be required. This analysis used present worth calcu- lations to compare numerous energy plans for Unalaska based on three possible load growth scenarios and three types of power systems. Binary and total flow geothermal systems of various sizes were analyzed to determine the optimum size for each of the three growth scenar- Denig-Chakroff and others ios.Each geothermal energy plan assumes an on-line date of 1990 and a 35-year useful life. The net present worth in 1985 of each geothermal power plan is "compared to the net present worth of comparable diesel power system plans that would meet the demands of the respective growth scenarios over the same period. The choice of geothermal systems analyzed and the system cost estimates were based on the actual reservoir characteristics,logistics of development and operation,and market con- ditions.Since the exploration well is be- lieved to have encountered a high conductivity fracture that communicates with a geothermal reservoir some distance away,there is no guarantee that a well at a second location in the vicinity of the exploration well will encounter an equally productive resource. Consequently,geothermal!power conversion systems with high resource use factors were an- alyzed so that the economics could be based on an assumption of drilling a single commercial- size well at the exploration wellsite.Because the geothermal fluids encountered are of excellent quality with respect to undesirable constituents and total dissolved solids,power system costs were considered both with and without the need for an injection well. Preliminary hydrologic data indicate that geothermal effluent may be disposed of in surface drainage without adversely affecting the environment.Consequently,the results presented here assume that reinjection will not be required.Due to the remote location of the site,conservative cost estimates for a road and transmission line were used,and the total cost of each geothermal power system was subjected to a 20%contingency factor.Final- ly,because of the relatively low demand at Unalaska,only geothermal power systems that . are cost competitive in smal]unit sizes were considered. The electric load forecasts used in the analysis were based on three population growth scenarios over a 20-year planning period(1985-2005).Populations and loads were assumed to remain level from year 2005 until 2025--the end of the 40-year period used for the economic analysis.A 2%annual increase in population was considered to be a minimum and somewhat conservative growth scenario for the planning period.A 4%growth scenario was analyzed as a reasonable expectation of moderate growth.An 11%growth scenario was considered,based on a population projection byDamesandMoore(1982)which assumed a low level of bottomfish harvest and processing on the island.For each growth scenario,electric load forecasts were developed for residential, commercial,and industrial users and for city services.Figure 2 illustrates the total electric load forecast for each growth scenario. Denig-Chakroff and others A diesel power system plan was developedasthe"base case"to compare the geothermal power system plans under consideration.A dieselgeneratorcapacityaddition/replacement schedulewasdevisedsuchthattheneedsprojectedinthe electric load forecasts would be met even with the largest power unit down for maintenance.Thereplacementschedulewasbasedonanassumption that diesel generators have a 20-year usefullife.A separate diesel power system plan wasdevelopedforeachofthethreegrowthscenarios. UNALASKA/DUTCH HARBOR TOTAL LOAD FORECAST MR grewth sceneries ENERGYUSE(uwWhyyr)(Troucsende)4%growth scenarie mo 2%growth ocenarie Figure 2.Graph showing the total electric load forecast for Unalaska/Dutch Harbor from 1985 to 2025. The geothermal power system plans weredevelopedbyassumingthatoneormoregeothermalunitswouldcomeonlinein1990.Geothermal units were based on net MW deliverable to the power grid after making deductions necessary to supply station service.Ten geothermal power plans were analyzed for each of the three growth scenarios.These included plans for installing from one to six 2.1 MW net total flow geothermal units and from one to four 3.35 MW net binary geothermal units.It was assumed that the geothermal units would produce 90%of the annual energy demand or 90%of the potential net production of the geothermal system,whicheverwasless.The remaining energy demand would be met with backup diesel generators. The net present worth of each power system plan was calculated using a 3.5%annual discount rate.Geothermal system construction costs weretakenfromRepublicGeothermal,Inc.(1984c)and modified to reflect a 20%contingency factor. Construction of a 34.5 kv transmission Tine and a road to the geothermal site were estimated at $15.473 million,including a 30%contingency factor.Diesel fuel prices were held constant through 1988 and then were escalated at 3.0%per year until 2010.Fuel costs were based on a production of 12 kilowatt-hours per gallon of fuel.Diesel generator cost and salvage value were estimated at $700 per kilowatt of installed capacity.Annual operation and maintenancecostswereassignedconstantvaluesof $1.012 million for the "base case"diesel system and $1.275 million for the geothermal systems. RESULTS The net present worth was calculated for each power system plan.The net present worth of the optimum systems analyzed is depicted in Figure 3.Geothermal system plans were compared to the diesel system plan for each respective growth scenario using acost-to-cost ratio (Figure 4).For the 2% scenario,the diesel/total flow cost-to-cost ratio fs very near unity for all sizes of the geothermal system considered.With the binary system,at 2%growth,the cost-to-cost ratio is at unity for a 3.35 MW unit and declines to .73 for a 13.4 MW system.Considering a 4%growth scenario,the optimum total flow system is 4.2 MW with a 1.23 cost-to-cost ratio and the optimum binary system is 3.35 MW with a 1.14 ratio.At 11%growth,the geothermal systems are clearly more economical than the diesel plan considered,with optimum cost/cost ratios of 1.80 for a 13.4 MW binary system and 2.05 for a 12.6 MW total flow system. 'COST OF OPTIMUM POWER PLAN 22 AND 4%GROWTH SCENAnIOS NETPRESENTWORTHOsihene)4%seoneric ZZ]dtecet biucry ER)total New 41%CROWTH SCENARIO RetPAZGENTwoatH(ititiione)s111%seonerte CZ tose blaery SE]total Now Figure 3.Graphs showing the net present worth of optimum power system plans forthreegrowthscenarios. oercageeeemerSereDenig-Chakroff and others COST/COST RATIO DIESEL VS TOTAL FLOW SYSTEM c"CRATIO0.9 t ;:r q 2.1 4.2 6.3 8.4 10.5 12.8 NET GEOTHERMAL CAPACITY (MW)is)2%scenario +4%scenario °11%scenario A DIESEL VS BINARY SYSTEM 1.8 -b 1.7 + 1.6 + 1.47 c/YCRATIO-_eo1.2 - 0.7 T T 3.35 6.70 10.05 13.40 NET GEOTHERMAL CAPACITY (MW) 2%scenario +4%scenario °11%scenario Figure 4.Graphs showing the cost/cost ratios of diesel power system plans to geothermal power system plans for three growth scenarios. Denig-Chakroff and others CONCLUSIONS Although this is a very preliminary economicanalysis,some general conclusfons can be drawnfromtheresults.It appears that a geothermal power system may be competitive with a dieselpowersystemonUnalaskaIsland.Major factorscontributingtotheeconomicfeasibilityofageothermalsystemarethecharacteristicsoftheresource,the logistics of development and operation,and the power market conditions.In the case of Unalaska,construction and operation costs can be developed with a fair amount of certainty because the characteristics of the geothermal fluid and the deliverability of the reservoir have been well defined through flowtestsandreservoiranalyses(Economides and others,1985).Major factors affecting the logistics of development have also been ascer- tained.Factors that are not known with the same degree of certainty are the future load growth of the community,the projected escalation rate of diesel fuel prices,and whether reinjection of geothermal fluids is necessary.Aspects of development that have not been addressed in this analysis,but which may have an effect on the feasibility of a geothermal project,are the potential benefits that may be achieved from utilizing waste heat from the diesel power system for district heating in the community and the potential for cascading uses of the spent geothermal fluid after it leaves the power plant. Based on this preliminary economic analysis,a more detailed study should be conducted to determine the feasibility of developing the Makushin geothermal reservoir for power generation on Unalaska Island,concentrating on load projections and market conditions in the community of Unalaska. ACKNOWLEDGMENTS The authors wish to extend a_sincere expression of gratitude to Nancy Gross and Jeff Currier of the City of Unalaska and to Brent Petrie,Bob Loeffler,and Irene Tomory of the Alaska Power Authority for their assistance and support. REFERENCES Dames and Moore,1982.Aleutian regional airport,project documentation,report for the City of Unalaska,p.44-45, Economides,M.J.,Morris,C.W.,and Campbell, D.A.,1985.Evaluation of the Makushin geothermal reservoir,Unalaska Island, Proceedings of the Tenth Workshop on Geothermal Reservoir Engineering,SGP-TR-84, Stanford University,Stanford,Ca.,in press. Morrison-Knudson Company,Inc.,1981.Geother- mal potential in the Aleutians:Unalaska, report for the Alaska Division of Energy and Power Development,p.2-5. Reeder,J.W.,Denig-Chakroff,0.,and Economides,M.J.,1985.The geology and geothermal resource of the Makushin vol- cano region of Unalaska Island,Alaska, Transactions of the 1985 International Symposium on Geothermal Energy,Kailua- Kona,Hawafi,in press. Republic Geothermal,Inc.,1983.Unalaska geo- thermal project,phase IB final report for the Alaska Power Authority contract CC-08-2334,v.1,p.2.: Republic Geothermal,Inc.,1984a.The Unalaska geothermal exploration project,phase I! final report for the Alaska Power Authority,contract CC-08-2334,p.Xx19- X25. Republic Geothermal,Inc.,1984b.The Unalaska geothermal exploration project,executive final report for the Alaska Power Authority,contract CC-08-2334,p.16-18. Republic Geothermal,Inc.,1984c.The Unalaska geothermal exploration project:electrical power generation analysis,final report for the Alaska Power Authority,contract CC-08-2334,p.48-51. SELOS.OZ, THE GEOLOGY AND GEOTHERMAL RESOURCE OF THE MAKUSHIN VOLCANO REGION OF UNALASKA ISLAND,ALASKA John W.Reeder (1)|David Denig-Chakroff!2),and Michael J.Economides!3) (1)Alaska Division of Geological and Geophysical Surveys,Pouch 7-028,Anchorage, Alaska 99510,U.S.A. (2)Alaska Power Authority,334 West 5th Ave.,Anchorage,Alaska 99501,U.S.A.(3)Dowell-Schlumberger,Marble Arch House,66/68 Seymour St.,London WIHSAF,U.K. ABSTRACT Geological,geophysical,geochemical,andwellflow-test data suggest a 13+km™and a slightly less than 193°C water-dominated reservoirbeneaththeMakushinVolcanocalderathatreaches a depth of about 4.4+km.Through numerous fractures,this reservoir is presently discharging on the northern,eastern,and southern flanks of the volcano as reflected by numerous fumaroles. Rising gases are also escaping directly to thesurfacethroughthecalderaasreflectedbythe largest fumarole on the summit caldera. INTRODUCTION The Makushin Volcano region of Unalaska Island,which is located in the eastern part of the Aleutian Islands,has been the site of a State of Alaska geothermal exploration program. Following extensive geological,geophysical,and geochemical investigations of the region,a 593 m exploratory well was drilled by Republic Geothermal,Inc.This well encountered a 192.8°C water-dominated reservoir that has a 2.04 to 2.17(kg/hr )/(N/m°)productivity index (Economides andothers,1985).A very large water-dominated geothermal reservoir exists in the Makushin Volcano region. The objective of this paper is to develop a geothermal model for the Makushin Volcano region. This model will be based on geology,which in addition to general geology will includegeothermalsurfacemanifestations,faults,well tests,gravity,and whole-rock geochemistry. GEOLOGIC SETTING The Aleutian arc is part of a ridge-trench system associated with active volcanism and seismicity.For the Unalaska Island region ofthisarc,the Aleutian trench is located about 180 km to the south.The floor of the Pacific Ocean (Pacific Plate)approaches the Aleutian arc (NorthAmericanPlate)in a NW direction at a rate of about 7 cm/yr (Minster and others,1974)where thePacificPlateisbeingsubductedundertheNorth American Plate at the Aleutian trench. The rocks of Unalaska Island include an older group of altered sedimentary and volcanic rocksdesignatedtheUnalaskaFormationbyDrewesandothers(1961),a group of intermediate-ageplutonicrocksthathaveintrudedtheUnalaskaFormation,and a younger group of unalteredvolcanicrocks(fig.1).The region SE of Makushin Volcano consists mainly of rock exposures belonging to the Unalaska Formation,whereasunalteredvolcanicsmakeuptheMakushinVolcano and most of the rock exposures to the NW of a line extending from Pakushin Cone to Table TopMountain(fig.1). The Unalaska Formation is upper Oligocene to middle Miocene (30 to 15 mybp)as based on fossils(Lankford and Hill,1979;and Drewes and others, 1961).This formation in the N part of Unalaska Island consists of conglomerate and sandstone units,and of numerous volcanic lava and breccia flows with some suspected volcanic sills. The Unalaska Formation has been intruded by three plutons and several smaller intrusive bodies.Individual plutons are zoned from mafic margins to felsic interiors and show calc-alkaline chemical characteristics (Perfit and others, 1980).Radiometric ages determined for two oftheseplutonsyieldedagesof11+mybp (Marlow andones1973)and 13+mybp (Lankford and Hill,1979). The Makushin Volcano of Unalaska Island is one of at least 36 volcanoes on the Aleutian arc that have been active since 1760 (Coats,1950). The top of the volcano is dominated by a 2.4 km diameter caldera that erupted about 8,000 ybp(Reeder,1983).The most recent eruptions of Makushin Volcano occurred in 1938,1951,and 1980(?)as small flank eruptions with the 1938 event being the largest (Simkin and others,1981). The unaltered volcanics unconformably blanket the Unalaska Formation as well as any intermediate age plutonics that have intruded it.Most of these unaltered volcanics are pre-Holocene and post-Pliocene,and have been derived mainly fromtheimmediateMakushinVolcanoregion.Except forPakushinCone,Wide Bay Cone,and the Point Kadin cones,the volcanic cones of the area have Reeder and others 10 Km Bering A agese xinokayde Driftwood mA Bay f. NORTH Bishop Pt. Pt.Kadin 53°45' Makushin Bay fF «Table Top-Mtn.¥G. MF "Tt | Sea 166°30' §4°- Unalaska Bay Map Symbols Fumarole field Warm.and/or hot springs Recent volcanic vent Caldera Unaltered volcanic rocks Plutonic rocks Unalaska Formation --w-Fault:dashed where approximate aoF\-map location (Northern part of Unalaska Island) Figure 1.A simplified geologic map of the northern part of Unalaska Island,after Drewes and others(1961)and Reeder and others (1985c). Bouguer gravity profile in figure 2. undergone intense glacial erosion,which occurred before 11,000 ybp (Black,1976).The Point Kadin cones as well as the Sugarloaf Cone occurred at about or shortly after the time of the Makushincalderaeruptionevent(Reeder and others,1985b). GEOTHERMAL SURFACE MANIFESTATIONS During regional geologic investigations of Unalaska Island during the summer of 1980, previously unreported active fumaroles and hot springs were discovered on the flanks of MakushinVolcano(Reeder,1982).Of the eight majorfumaroleareas(fig.1),only fumaroles no.3 and The A-A'line is the location of the complete no.5 (Drewes and others,1961)and fumarole no.6 (Maddren,1919)had previously been reported.Of these fumaroles,only the large plume from fumarole no.6 can be seen from Unalaska,the only community on Unalaska Island. Some warm and hot springs exist in or at lower elevations to the fumaroles.These springs are rich in HCO.,SO,,and Ca.They haveapparentlyoriginatedfrommeteoricwatersthat, after infiltration into fractured rock,have been heated by ascending gases and/or by conductionrom,wall rock (Motyka and others,1983).The"He/"He compositions of these rising gases as determined by Motyka and others indicate adefinitemagmaticinfluence.The fumarolicactivityisevidenceforatleastashallowvapor-dominated zone beneath each fumarole. FAULTS Faults,mostly near vertical and having smal] displacements,are found throughout the region. In a few cases,faults have been found trending directly into Quaternary volcano centers such asPakushinCone,Sugarloaf Cone,and even activeMakushinVolcano(Reeder and others,1985b).The location of nearly all of the fumaroles appear tobeatleastpartlycontrolledbyfaults(fig.1). For example,an EW striking fault and a N 50°W striking fault have been recognized as intersecting at fumarote no.1 (Reeder and others, 1985c;and fig.1). Many of the fractures of the northern part of Unalaska Island reflect orientations expected for a regional stress caused by the subduction of the Pacific Plate,namely an approximately N 50°W striking set with approximate corresponding N 05° W,N 40°E,and N 85°E€sets (Reeder,1985). Another observed N 68°W striking set has been explained by Reeder as being caused by the late Miocene rotation of the northern part of Unalaska Istand.These fractures,before this rotation, would have had the expected N 50°W strike. WELL TESTS Three temperature gradient holes were drilled in 1982 to depths of 460 m on the lower flanks of Makushin Volcano,and encountered temperatures of up to 195°C.These holes were drilled by Republic Geothermal,Inc.under the Alaska Power Authority contract.These holes and their temperature gradients are described by Isselhardt and others(1983a). In the summer of 1983,an exploratory wellwasdrillednearfumaroleno.1 (fig.1),a siteoriginallysuggestedbyReederandothers(1982). This well encountered a steam zone in fractured mafic crystalline rock (gabbro-norite)at 205 m depth and then encountered a water-dominated zone at a large fracture,also in mafic crystalline rock,at 593 m depth.These waters were moderately saline,low-bicarbonate waters at a temperature of 192.8°C ang at a static bottomholepressureof3.4 x 10°N/m"gage. Several static temperature profiles of this well were obtained by Republic Geothermal,Inc. These surveys indicated that the well,which islocatedatabout360ma.s.1.(above sea level), has a steam zone with a vapor-liquid interface atadepthof250m(110 ma.s.1.).Below this depth is a liquid zone,which increases to a maximum temperature of 203.9°C at a 457 m depth,thendeclinesslowlytoatemperatureof201.7°C at thebottomofthehole. A 34 day flow test was performed on this well as described by Campbell and Economides (1983)andEconomidesandothers(1985).Sustained flow Reeder and others through a 7.6 cm diameter well of 28,600 kg/hr was achieved for 19 days of this test with less than6.9 x 10°N/m”of pressure girawdpwn from abottomholepressureof3.4 x 10°N/m"gage.The well productivity index that was obtained from thetestwas2.04 to 2.17 (kg/hr)/(N/m°).As based on a simple material balance calculation that assumes a constant total compressibility for the system,Economides and others (1985)gstimated a reservoirmassofabout3.1 x 10°"kg.For this detepmination,a water compressibility of 4.351 x1040mo/N and a rock compressibility of 8.702 x10m°/N were assumed.Such a reservoir mass would equate to a water volume of about 3.1 km”. GRAVITY A total of 155 gravity stations have been obtained for the northern part of Unalaska Island(Reeder and others,1985a).Figure 2 shows a complete Bouguer gravity profile across Makushin Volcano.Based on two-dimensional modeling,thedense(2.8 gm/cc)mafic crystalline rocks,whichareexposedjustSEofMakushinVolcano(fig.1),underlie the entire region (Reeder and others, 1985a;and fig.2).The only area where this dense rock might not be continuous would be along a linear NE oriented gravity low that passes directly through the Makushin caldera.This gravity anomaly has been interpreted by Reeder and others as a NE oriented fracture zone within the crystalline rocks that has been covered by Makushin volcanics. The most prominent gravity low occurs directly over the caldera of Makushin Volcano (fig.1).Such an anomaly is probably due to the very porous nature of the body of "broken-up"rock debris that fills the caldera.Such a geologic formation is the most likely,candidate in thisregionforcontianinga3+km?body of water. 'A DISTANCE (km)A»1,"4 ©1,6 1 2 rt4o COMPLETE Regional | BOUGUER 129 GRAVITY (Density 2.6) -(mgal) °Observed 100 yt t L ri 1 fo#a/ N RESIDUAL GRAVITYb-10 (mgal)ON *Calculated [-20 18 14 10 6 2iirTLLa41irt4 1. 2.48 2.1 [2.8 2.5oe 2 DEPTH 2.3 (km) 2.8 2.8 DENSITY MODEL (gm/cc) Figure 2.Gravity profiles and crustal density cross section for line A-A'of fig.1. Reeder and others The caldera may be modeled as a verticalcylinderwithaconservativeradiusof1.29 km. The caldera fill has been determined to have a bulk density between 2.0 and 2.2 gm/cc,and altered Makushin volcanics have been found to have an average density of about 2.62 gm/cc (Reeder andothers,1985a).If the average bulk density of the caldera fill is taken as 2.1 gm/cc,then the porosity of the fill would be about 20%if the actual rock density of the fill is 2.62 gm/cc. Because the vapor-liquid interface occurred atabouta110melevationa.s.1.at the exploratory well,then let's assume water saturation occurs also at this same elevation within the caldera. Then,the 1850 m a.s.1.Makushin caldera may be modeled as a 2.1 gm/cc cylinder to a depth of 1740m(110 m elev.)that is flanked by denser Makushin volcanics.Then the cylinder may be extended in depth at a 2.26 gm/cc bulk density for watersaturatedfill. observed gravity profile,such a cylinder would need to be extended to a depth of 2.62 km below the initial water saturation elevation,which would be to a depth of 2.51 km b.s.1.(fig.2). In summary,the Makushin caldera has just been modeled as a 4.36 km vertical cylinder with a 1.29 km radius that is filled with fairly porousmaterial.If the bottom 2.62 km of this cylinder is actually saturated to 20%of volume with water, then the Makushin caldera would contain about 2.7km”of water within a 13.6 km region.Thisvolumeofwaterisonlysjightlylessthanthecalculatedvolumeof3.1 km”as based on the well test. WHOLE-ROCK CHEMISTRY With respect to the nature of the resource, the characteristics of the heat source are important.Two generic types of geothermal resources have in general been recognized based on the origin of heat that drives their convective circulation systems.These generic systems,in turn,correspond to high temperature (greater than200°C)versus moderate to low temperature resources.The classic major geothermal systems around the world,such as those at Wairakei,New Zealand;at The Geysers of California,U.S.A.3 and at Larderello,Italy are all associated with less than 1 million year old igneous systems that consist of a high silicic magma such as rhyoliteordacite(McNitt,1970).By contrast,most other volcanic and/or plutonic igneous occurrences that do not consist of high silicic melts do not have associated high temperature hydrothermal systems. Rhyolitic and dacitic rocks are lacking for a majority of the 36 plus active volcanoes of theAleutianarc(Coats,1962).Thus,these active volcanoes are most likely associated with low to- moderate temperature geothermal systems. Nevertheless,the larger andesitic volcanoes maybeunderlainbytrappedmagmathathasrisenfrom great depths.Such shallow magma bodies mightserveasasignificantheatsourceforlargemoderatetemperaturegeothermalsystems. In order to obtain a fit with the The Makushin Volcano of Unalaska Island is typical of such large andesitic volcanoes.The Makushin volcanic field is dominantly a tholeiiticprovince(fig.3).The tholeiitic volcanoes of the Aleutian arc are large centers where magmas can more easily reach shallow depths unlike the smaller calc-alkaline centers.Tectonically caused deep fractures and large crustal rotations as previously discussed under the fault section could help encourage the rapid rise of such magmas.Once such magmas reach shallow depths,they can undergo shallow,closed =systemdifferentation(Kay and others,1982).The. tholeiitic magmas show a Fe enrichment trend (fig.3),which is consistent with low-pressure and.high-temperature crystallization in a _largeshallowmagmabody. Part of the shallow magma body underneath Makushin Volcano has been violently extruded from the system as reflected by the existence of a Makushin caldera.Magma probably still remains beneath and around the caldera fill,and it is this magma that would be the principal drivingheatsourcefortheMakushingeothermalsystem. Based on the gravity model,such magma would bedeeperthan2.51 km b.s.1.immediately beneath thecalderabutcouldbeatshallowerelevations beneath its flanks. 1 in 1 nl L n 1 4 rn 1 1 744 VOLCANOES r 2 FeO*/MgO Fed'(total Fe as Fe0)/MgO ratio versusSi0,for Quaternary volcanic rocks ofthe"northern part of Unalaska Island as shown in figure 1.The calc-alkaline(CA)and tholeiite (TH)boundary lineisfromMiyashiro(1974).Data is from samples that were collected by Reeder and others (1985c). Figure 3. DISCUSSION A large water-dominated reservoir exists beneath the Makushin caldera at a depth of 1.74: km to 4.36+km beneath the summit.Rising gases from this hot water reservoir are presently escaping to the surface through the caldera fill as reflected by the largest fumarole near the summit of the volcano.Through the numerous fractures,this reservoir is also discharging fluids to the N,E,and S,as reflected by the numerous fumaroles on the N,E,and S flanks of the volcano (fig.1).Such fluids,as they slowly move along fractures within the dense mafic crystalline rocks of the region,may slowly gainheatbyconductionfromwallrock.For example, the highest static temperature observed in the exploratory well was 203.9°C,and yet the inflowing bottomhole fluids remained at a constant 192.8°C temperature.This exploratory well, possibly by means of the recognized E-W strikingfracture(fig.1),is in direct hydraulic connection to the Makushin geothermal reservoir. Nevertheless,the inflowing 192.8°C fluids have probably been heated by the massive crystalline rocks,and such fluids are probably slightly warmer than the main Makushin geothermalreservoir.Recharge might be occurring veryslowlyfromtheWflankofthevolcanoaswellas from the summit region. It is possible that large quantities of hot water may also be located beneath the flanks of the volcano,especially beneath its NE and SW flanks where gravity has suggested a fairly large NE striking rift zone.Indeed,fumaroles no.5 and no.7 are located directly over this zone,and they represent the presence of at least some fluids within this zone.Nevertheless,largequantitiesofandesiticand=basaltic lavaextrusionshaveoccurredonboththeSandN flanks of this volcano during the Holocene (Reederandothers,1985b).Such large quantities of lava extrusion have occurred with no indication of any large phreatomagmatic explosions,which would be expected if magma came into contact with large ground-water bodies. In contrast,over 0.21 km?of phreatomagmatic fiow deposits have been recognized as originating directly from the Makushin caldera during its8,000 ybp eruptive activity (Reeder,1982;andReederandothers,1985b).This suggest that a caldera and a ground-water reservoir within the caldera might have existed before the large 8,000 -ybp phreatomagmatic eruption.If magma is everintroducedagainintotheMakushingeothermalreservoir,large phreatomagmatic eruptions would be expected.Such phreatomagmatic eruptions mayrepresenttheprincipalcauseforcaldera formation in the Aleutian arc. The Makushin geothermal reservoir has been "suggested to be confined to a 3 km wide NE oriented fracture zone underneath fumaroles no.1, 2,and 3 (Isselhardt and others,1983b).Field observations (Reeder and others,1985c)and gravity modeling (Reeder and others,1985a) indicate the lack of any such highly fractured NE Reeder and others striking zone.In addition,the flowing bottomhole fluid temperature in the exploration well near fumarole no.1 was 192.8°C.This temperature is Tower than the measured static temperature of 201.7°C at that same depth.This phenomenon,coupled with an observed static temperature gradient reversal from a 203.9°C maximum,indicates that the reservoir proper is actually located some distance from the well and not just beneath it. CONCLUSION The most likely place for a large geothermalsystemasrepresentedbyabout3km”of water at slightly less than 192°C would be within the Makushin caldera at a depth of up to 4.4 km.Such hot water would discharge gases through the caldera fill,which is reflected by the largestfumarolenearthetopofthevolcano.Hot waters would also slowly discharge along fractures,whichisreflectedbyfumarolesontheN,E,and § flanks of the volcano. Although this is a very simplistic model and not one without flaws,it does appear to be the only model that fits the limited amount of data presently avajlable.Most geothermal reservoirs in the world that are associated with Quaternaryvolcanoesarewithincalderastructures(McNitt,1970).The Makushin geothermal reservoir appearstobeanotherthatshouldbeaddedtothelist. ACKNOWLEDGMENTS Special thanks is given to the people ofUnalaskafortheircontinuoussupportofal] aspects of this investigation.In addition,veryspecialthanksisgiventoAbi&Jim Dickson, Kathy &Bob Grimnes,Nancy Gross,and the CurrierfamilyfortheirhelpinkeepingReeder,duringhismanyyearsofdifficultfieldwork,from getting lost in the famous Aleutian fog. REFERENCES Black,R.F.,1976.Geology of Umnak Island eastern Aleutians as related to the Aleuts, Arctic and Alpine Research,v.8(1),p.7-35. Campbell,D.A.,and Economides,M.J.1983.A summary of geothermal exploration and data from stratigraphic test well no.1,Makushin Volcano,Unalaska Island,Proceedings of the Ninth Workshop on Geothermal Reservoir Engineering,SGP-TR-74,Stanford University,Stanford,Ca.,p.167-174. Coats,R.R.,1950.Volcanic activity in the Aleutian arc,U.S.Geological SurveyBulletin974-B,p.35-49. Coats,R.R.,1962.Magma type and crustal structure in the Aleutian arc,in The Crust of the Pacific Basin,G.A.MacDonald and H. Kuno,Editors,American Geophysical Union Monograph Number 6,p.92-109. Reeder and others Drewes,H.,Fraser,G.D.,Barnett,H.F.,Jr.,1961.Geology of Unalaska Island and adjacent insular shelf, Aleutian Islands,Alaska,U.S.Geological Survey Bulletin 1028-S,p.583-676. Economides,M.J.,Morris,C.W.,and Campbell, D.A.,1985.Evaluation of the Makushin geothermal reservoir,Unalaska Island, Proceedings of the Tenth Workshop on Geothermal Reservoir Engineering,SGP-TR-84, Stanford University,Stanford,Ca.,in press. Isselhardt,C.F.,Matlick,J.S.,Parmentier,P.P., and Bamford,R.W.,1983a.Temperature gradient hole results from Makushin geothermal area,Unalaska Island,Alaska, Geothermal Resource Council Transactions,v. 7,p.95-98. Isselhardt,C.F.,Motyka,R.,Matlick,J.S., Parmentier,P.P.,and Huttrer,G.W.,1983. Geothermal resource model for the Makushin geothermal area,Unalaska Island,Alaska, Geothermal Resource Council Transactions,v. 7,p.99-102. Kay,S.M.,Kay,R.W.,and Citron,G.P.,1982.Tectonic controls on tholeiitic and calc-alkaline magmatism in the Aleutian arc,Journal of Geophysical Research,v.87(85), p.4051-4072. Lankford,S.M.and Hill,J.M.,1979.Stratigraphy and depositional environment of the Dutch Harbor Member of the Unalaska Formation, Unataska,Alaska,U.S$.Geological Survey Bulletin 1457-B,p.1-14. Maddren,A.G.,1919.Sulphur on Unalaska and Akun Islands and near Stepovak Bay,Alaska,U.S. Geological Survey Bulletin 692,P.283-298. Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,T.R.,1973.Tectonic history of thecentralAleutianarc,The Geological Society of America Bulletin,v.84,p.1555-1574. McNitt,J.R.,1970.The geologic environment of geothermal fields as a guide to exploration,Proceedings of the United Nations SymposiumontheDevelopmentandUtilizationof Geothermal Resources,Geothermics,Special Issue 2,v.1,p.24-31. Minster,J.B.,Jordan,T.H.,Molnar,P.,and Haines,E.,1974.Numerical modeling of instantaneous plate tectonics,Geophysical Journal of the Royal Astronomical Society,v. 36,p.541-575. Miyashiro,A.,1974.Volcanic rock series inislandarcsandactivecontinentalmargins, American Journal of Science,v.274,p. 321-355. Snyder,G.L.,and Motyka,R.d.,Moorman,M.A.,and Poreda,R.,1983. Progress report -Therma]fluid investigations of the Makushin geothermalarea,Alaska Div.of Geol.&Geophys.Surveys Report of Investigations 83-15,52 pp. Perfit,M.R.,Brueckner,H.,Lawrence,J.R.,and Kay,R.W.,1980.Trace element and isotopic variations in a zoned pluton and associated rocks,Unalaska Island,Alaska:A model for fractionation in the Aleutian calc-alkaline suite,Contrib.Min.Pet.,v.73,p.69-87. Reeder,J.W.,1982.Hydrothermal resources of Makushin Volcano region of Unalaska Island, Alaska,in Circum-Pacific Energy and Mineral Resources Conference,3rd,S.T.Watson, Editor,American Assoc.of Petroleum Geologist Circum-Pacific Series,p.441-450. Reeder,J.W.,1983.Preliminary dating of the caldera forming Holocene volcanic events for the eastern Aleutian Islands,The Geological Society of America 1983 Annual Meeting,Abstracts with Programs,v.15(6),p.668. Reeder,J.W.,1985.An analysis of fault and volcanic dike orientations for the Makushin Volcano region of the Aleutian arc,The Royal Society of New Zealand Bulletin,in press. Reeder,J.W.,Economides,M.J.,and Markle,D.R., 1982.Economic and engineering considerations for geothermal development in the Makushin Volcano region of Unalaska Island,Alaska,Geothermal Resource Council Transactions,v.6,p.385-388. Reeder,J.W.,Edge,D.B.,and Swanson,K.E.,1985(a).Complete Bouguer gravity map of the Makushin Volcano and Dutch Harbor region of Unalaska Island,Alaska,Alaska Div.of Geol. &Geophy.Surveys Report of Investigation,1 plate,in press. Reeder,J.W.,Swanson,D.E.,and Larsen,M.J., 1985(b).Unconsolidated deposits and geologically Recent volcanic rocks and faults of the Makushin Volcano and Dutch Harbor region,Unalaska Island,Alaska,Alaska Div. of Geol.&Geophy.Surveys Report of Investigation,1 plate,in press. Reeder,J.W.,Swanson,K.E.,Larsen,M.J.,and Edge,D0.B.,1985(c).Geologic bedrock observation and map of the Makushin Volcano and Dutch Harbor Region,Unalaska Island, Alaska.Alaska Div.of Geol.&Geophy. Surveys Report of Investigations,2 plate,in press. Simkin,T.,Siebert,L.,McClelland,L.,Bridge, D.,Newhall,C.,and Latter,J.H.,1981. Volcanoes of the World,A Regional Directory, Gazetteer,and Chronology of Volcanism during the Last 10,000 Years,Smithsonian Institute, Hutchinson Ross Pub.Co.,Stroudsburg,Penn., 232 pp. Geothermal Energy in the ALEUTIANS An Untapped Resource ee, State of Alaska Dept.of Commerce &Economic Development Division of Energy &Power Development 1981 Introduction Unalaska stands at the crossroads of the Aleutians, and could play a major role in the developing bot- tomfish industry and outer continental shelf oil, gas and mineral production.To meet the energy demands of an expanding industrial base,Una- laska needs to develop an inexpensive,reliable supply of energy.Geothermal resources can play an important part in Unalaska's energy picture and could be the key to total energy self-sufficiency. The result would be a stable,resource based economy for this Alaskan community. DRIFTWOOD,BAY jor Unalaska Island Unalaska Island is part of the Aleutian Chain,an arc of active volcanos extending 1400 miles from the Alaska Peninsula to the Kamchatka Peninsula of Russia.The town of Unalaska is a traditional Aleut village.The port of Dutch Harbor in the city of Unalaska became the nation's leading fishing port in 1979.King crab is by far the most important species,but markets are developing for tanner crab and bottomfish. Unalaska is prospering due to its excellent harbor and strategic location on the shipping routes to the western Alaska mainland,the North Slope,and the Aleutians.The official 1970 census listed a popula- tion of 342;by 1980 the population had grown to 1322.During the peak fishing season,the popula- tion swells to over 5000,and the continued growth of the town is a certainty.Expansion of its role as a transhipment point (it is the only place between Kodiak and Yokohama that a container ship can dock),outer continental shelf oil and gas explora- tion,and increased bottom fishing by the U.S.tn the Bering Sea guarantee a prosperous and flourishing future. Diesel currently supplies all of the energy on the island.The city-owned electric utility primarily serves residential and small commercial users in Unalaska.All of the seafood processors have their own diesel generators to supply processing and domestic needs.Presently,the installed electric capacity on Unalaska is under 14,000 kilowatts.The BLM projects power demands exceeding 50,000 kilowatts by the year 2000.The city is considering establishing an REA and expanding the central util- ity system to meet industrial power demands. Energy costs on the island are high.The town passed a balanced budget for its electric utility in 1981,which could mean raising its rates from 17¢ per kilowatt-hour to 46¢per kilowatt-hour.At these rates,the annual power bill for a typical residence would be over $4000. Clearly,there is a critical need in Unalaska for: e Expanded electric capacity Central generation e Cheaper energy e Less dependence on fossil fuels Geothermal energy can help meet these goals. Geothermal -The Potential Geothermal energy is derived from the earth's in- terior heat.In areas where the earth's heat reaches close to the surface,there is the potential for economic energy recovery.Geothermal resources are particularly abundant in the Pacific "ring of fire,””a region of high volcanic and seismic activity resulting from shifting of the earth's plates.The Aleutian Islands are part of this "ring of fire.” There are three primary types of geothermal re- sources:hydrothermal,hot dry rock,and geopres- sured zones.Nearly all of the currently developed geothermal resources are hydrothermal systems, where naturally occurring ground water is heated at depth.These systems can be either vapor- dominated (steam)or hot water dominated,de- pending on temperature and pressure. The essential ingredients for a hydrothermal sys- tem are a heat source,a sufficient supply of ground water,and a mechanism for transporting the heated ground water to near the surface (por- ous rock or natural fractures).The two other types of geothermal resources are hot dry rock,which requires injecting water as a heat transfer medium, and geopressured zones,in which water is trapped with natural gas under thousands of feet of sedi- ments. The use of geothermal resources depends on the nature of the resource (temperature,quality,quan- tity)and the energy demand around it.Conven- tional generation of electricity usually requires re- source temperatures of about 350°F.Lower tem- perature resources can be utilized directly in such applications as space heating,aquaculture,and process heating. CONVENTIONAL (°360°)POWER PRODUCTION 180 350°and UP 340° 1602 320° ALUMINA PROCESSING |-300° DRYING FARM PRODUCTS |140°280° EXTRACTION OF SALTS |! |-|260° REFRIGERATION (mod.temp.)120° -240° CONCRETE BLOCK CURING |220° CRAB PROCESSING 100° l :200° DRYING FISH > SPACE HEATING bone 180°80 REFRIGERATION (low temp.)160° GREENHOUSES |60°|140° 120° BALNEOLOGICAL BATHS 3 SOIL_WARMING j 40°1002 FERMENTATION,DE-ICING. |goe FISH FARMING 20° -60° °C °F OY TYPICAL TEMPERATURES FOR GEOTHERMAL RESOURCE APPLICATIONS Geothermal on Unalaska Two areas with geothermal potential have been identified on Unalaska.The Summer Bay resource area includes a warm springs with a temperature of 95°F.At greater depths the resource is estimated to be 180°F.Potential economic uses for the Summer Bay resource include greenhousing,cement cur- ing,kelp processing,and aquaculture. GEOLOGIC CROSS-SECTION OF SUMMER BAY RESOURCE The Makushin Volcano is one of the most promis- ing geothermal prospects in Alaska.(The State has included 241,000 acres in the Makushin Potential Geothermal Resource Area.)Seven fumarole fields on the volcano are evidence of a high- temperature geothermal resource which could be developed for power production.Geologists esti- mate that development of these fumarole fields could supply at least 100,000 kilowatts of electricity. It is possible that a more extensive geothermal resource underlies the Makushin region.If so,the total power production potential could be several times greater. For more information about Unalaska's geothermal resources,contact: Don Markle or Duane Bessette Preliminary economic analyses indicate that de- velopment of a remote geothermal power plant on Makushin could produce power at costs that are less than the existing diesel system in Unalaska. Geothermal development or a combined geothermal/hydroelectric/gas turbine power sys- tem could provide a reliable,long-term economic power supply to meet all of Unalaska's projected energy needs and provide the necessary energy base for expansion of the local economy. Major tax incentives for geothermal developments, including intangible drilling costs,depletion allo- wances,and investment tax credits,have been enacted in recent federal energy legislation.In ad- dition,the State of Alaska is actively involved in supporting power developments.In 1981,the State put $500 million into energy projects on a grant basis.The State provides power development loans at low interest rates.With the reliable energy market in Unalaska and the opportunity for crea- tive financing,geothermal energy development on Unalaska would be a relatively low risk venture. FUMAROLES Alaska Dept.of Commerce &Economic Development Division of Energy &Power Development 338 Denali Anchorage,AK 99501 (907)276-0508 Photos by John Reeder GEOLOGIC CROSS-SECTION OF MAKUSHIN VOLCANO RESOURCE Exploration drilling is needed to define the re- source before substantial development can occur. The State is investing $5 million in resource con- firmation drilling on Makushin this year.Energy is needed before Unalaska can expand its industrial potential.Development of Unalaska's geothermal resources could stimulate the area's economic growth through development of a competitive and reliable energy supply. MORRISON KNUDSEN Funded by the U.S.Dept.of Energy onSn ,$%57.08 'fy ;. . ;/RECEIVED GEOLOGICAL AND ENGINEERING STUDIES FOR 7GEOTHERMALDEVELOPMENTONUNALASKAISLANDNOV27,G5" RLASYA POWER AUtiia5. John W.Reeder,Ph.D.*,Michael J.Economides,Ph.D.**,and Donald R.Markle****State of Alaska Division of Geological and Geophysical Surveys **kUniversity of Alaska,and***State of Alaska Division of Energy and Power Development,U.S.A. Summary Geothermal resource investigations on Unalaska Island have focused on the .Makushin Volcano and the Summer Bay regions,12 km and 3 km respectively from the.community of Unalaska.In total,8 fumarole fields have been located in the Makushin ;Volcano region.Large hydrothermal reservoirs,having temperatures in excess of: :150°C and extending to depths of about 2 km,are suspected to exist in the region marked by the fumarole fields on the southeast flank of Makuskin Volcano.The loca- tion of these southeast flanking fumarole fields are controlled by plutonic-metavol- canic boundaries and corresponding fractures,as well as by large northwest oriented. fracture systems that are interpreted to have been caused by tectonic stresses. In this paper geological and engineering considerations with respect to any poten- 'tial geothermal development in the Makushin Volcano region are presented.A plan for 'further exploration and exploratory drilling is also included. 1.INTRODUCTION Unalaska Island is part of the Aleutian Island a...The Makushin Volcano on Unalaska Island is one of at least 36 volcanoes on this island are which have been re- ported active since 1760 (Ref.1).Such volcanic regions,with shallow magma bodies and deep tectonic fracture systems,represent a favorable setting for the existence of large hydrothermal reservoirs. During volcano investigations in the Aleutian Islands,Drewes et al.(Ref.2) observed fumaroles and hot springs on the top and on the south flank of Makushin Vol- cano.Later,Miller and Smith (Ref.3)suggested that a high-level magma chamber exists under the summit caldera of this volcano.During more recent geologic investi- gations of Unalaska Island,Reeder (Refs.4 and 5)discovered active fumarole and hot-spring fields on the flanks of Makushin Volcano.Many of these fumarole fields are probably the surface expressions of vapor-dominated hydrothermal systems. The Unalaska community presently serves the largest American fishing fleet for the Bering and North Pacific region and it could play a major role in the development of a bottomfish industry.In addition there is nearby potential for outer continental. 'shelf oil,gas,and mineral production.Present peak electric utility demands for Unalaska is 15 MW,including both the publicly owned diesel generators and those operated by the private fish processors.Projections for future energy demands are risky,but peak demands by the year 2000 could reach between 30-60 MW in response to|: expanding resource industries. While a sizeable portion of the island population appears to be "prodevelopment,”- there are prominent forces that are apprehensive.Apart from any development,Unalaska needs to develop an inexpensive and reliable supply of energy.Geothermal resources| can play an important part in Unalaska's energy picture,and could be the key to total energy self-sufficiency. 2.FUMAROLE FIELDS A total of eight fumarole fields were examined by Reeder (Refs.4 and 5)in theMakushinVolcanoregionduringthesummersof1980and1981.They were arbitrarily-numbered for identification purposes in a clockwise direction.The location of these fumarole fields.are shown in Figs.1 and 5. The Unalaska fumarole fields vary in character and dimension.Fumarole field| no.1 consists of fumarolic activity (i.e.,at boiling point),of warm ground,and of outcrops of highly hydrothermally altered plutonic and metavolcanic rocks covering approximately a 120 m by 60 m region as shown in Fig.2.Field no.2 has fumarolic activity and warm ground covering a region about 1 km long and up to 400 m wide as- shown in Fig.3.Fig.3 also shows a region consisting of outcrops of highly hydrothermally altered plutonic and metavolcanic rocks.Like field no.2,field no.3 consists of fumarolic activity and warm ground covering a region about 500 m long> and about 450 m wide;a region also consisting of outcrops of highly hydrothermally altered plutonic and metavolvanic rocks.Field no.4 consist of fumarolic activity;covering a narrow region only about 60 m long,located along a stream and a lateral.moraine.Superheated fumarolic activity and warm ground covering a 90 m by 90 m- region of unaltered volcanic beccia occurs at field no.5.Field no.6 is a fairly|large steam vent on the top of Makushin Volcano.It occurs as shown in Fig.4 mainly|in a 100 m diameter region near a small dome of unknown composition and within the|remains of a small cinder cone partly covered with sulphur deposits.This field is found in the 3 km diameter ice-filled summit caldera of Makushin Volcano.Field no.|7 consists of minor activity located in a glacial till.Field no.8 consists of,minor fumarolic activity and hot rock positioned on top of a small knob located just| west of the Sugarloaf Cone,which is a region of unaltered basalts that have retained their constructional forms. Warm and hot water springs were found at lower elevations as shown in Fig.5. Initial water analyses of some of these hot and warm springs were done by Motyka et al. (Refs.6 and 7).Their.results indicated near neutral sodium/bicarbonate/sulphate waters that were similar in chemical character to hydrothermal waters described by Mahon et al.(Ref.8).the systems described by Mahon.ny of the hot spring waters consist predominantly ot meteoric waters which have be.heated by vapor dominated|hydrothermal systems generated from greater than 150°C alkali-chloride waters at greater depth.Because the level of the ionic composition in the fluids are different for springs near different .fumarole fields,the Makushin water analyses indicate thepossibilitythatseveralseparatehydrothermalsystemsexistintheregion. 3.GEOLOGIC SETTING The rocks of Unalaska Island include an older group of altered sedimentary and volcanic rocks designated the Unalaska Formation by Drewes et al.(Ref.2),a group of plutonic rocks intermediate in age,and a younger group of unaltered volcanic rocks. The rocks of the Unalaska Formation have been altered under conditions of the zeolite and/or lower greenschist facies.Perfit and Lawrence (Ref.9)argued that these rocks occurred mainly during the emplacement of the plutonic bodies.The region to the southeast of Makushin Volcano consists mainly of rock exposures of the Unalaska Forma-tion whereas unaltered volcanics make up the Makushin Volcano and most of the rock | exposures to.the northwest as shown in Fig.1.; i The Unalaska Formation in the region of fumarole fields no.1,no.2,and no.3 has been extensively intruded by plutonic bodies of gabbro and intermediate plutonic.'rocks.The intrusive bodies and the surrounding Unalaska Formation are extensively|fractured especially along contact boundaries.The fractures serve as conduits for. any hydrothermal convection at least near the ground surface.For example,a plutonic; body occupies the region between fields no.1 and no.2,where the hydrothermal surface;manifestations of fumarole fields no.1 and no.2 are oriented in a general northeast| direction along the northern and southern boundaries of this plutonic body respectively.| 'One prominent near vertical fracture on the northern boundary of this pluton strikes; 'east-west directly through fumarole field no.1. Several near vertical fractures,striking between N 40°W and N 70°W and appearing -.to be normal faults,were found near the vicinity of the fumarole fields as shown in Fig.1.Two of these faults,which strike about N 60°W and bound the field no.2,. 'extend nearly the entire length of the northern part of Unalaska Island;a distance:of over 36 km.These fractures are active since they disrupt soil horizons. The underthrusting of the Pacific plate under the North American plate causes| 'compressional stresses in the direction of plate convergeace in the arc region as' indicated by Nakamura (Ref.10).Because the motion of convergence of the Pacific'and North American plates at Unalaska is approximately in a N 45°W direction,these | near vertical northwest striking fractures are suspected to have been caused by compressional tectonic stresses.The fractures,even though they correlate with most of the fumarole fields,do not appear to influence the actual surface configurationofthehydrothermalmanifestations.Thus,these fractures do not appear to serve as' conduits near the ground surface for hydrothermal convection. For Makushin Volcano,Nakamura et al.(Ref.11)determined,based on the orienta- 'tion of flank eruptions,a maximum stress orientation of N 60°W where the expected azimuth should be about N 45°W.If the expected azimuth is the actual one,then the recognized fractures striking about N 60°W should contain a strike-slip component.As shown in Fig.1,one N 60°W striking fault in the community of Unalaska was found™ to have such a strike-slip component as based on observed slickensides. It is suspected that large hydrothermal convective systems exist in a northeast oriented zone as roughly marked by fields no.1,no.2,no.3,and no.4.Recent: 'lava flows (i.e.,flows that still retain details of their constructional forms)can' be found northwest of this zone as represented by the flows from the upper reaches of| Makushin Volcano and from the prominent rift zone near Point Kadin,northeast of this zone as represented by the flows surrounding the Sugarloaf Cone,and southwest of this zone as represented by the volcanic rocks of the Pakushin Cone.Yet,no recent volcanic extrusions have occurred within this northeast oriented zone nor from the region to the southeast.In fact no unaltered volcanic rocks have been recognized as” being extruded from this -ne,indicating that probably no magma extrusions have occur- red in this region for 2 last three million years as sed on the known range of radiometric age dates for unaltered volcanics describeu vy Cameron and Stone (Ref. 12).Such magma extrusions have not occurred either because the magma does not exist at depth or because magma exist at large depths where it might be more viscous than any magmas to the northeast or to the southwest.If such magma bodies exist in the region,they might have a dike-like configuration oriented in a direction corresponding to the N 60°W fractures shown in Fig.1.°Such deep magma bodies as well as any shallow magma bodies located near the volcanic centers to the west,northwest,and north could be the heat sources for large hydrothermal convective systems. In contrast,any hydrothermal convective systems linked to fumarole fields no. 5,no.6,no.7,and no.8 are suspected to be limited to shallow zones where any heat sources would also be at shallow depths.Such shallow heat sources might be due to the existence of recent surface volcanic flows that still contain heat as suspected at fumarole field no.8.Such shallow heat sources also might be due to the cooling of shallow magma bodies as reflected by the dome in field no.6. Most of the recent extrusive rocks (i.e.,volcanic rocks that still show their surface constructional form)in the northern part of Unalaska Island are porous basalt- ic rocks.Any heat contained in such.rocks have been mostly removed,except for small isolated areas such as the one found at field no.8.Hydrothermal convective systems might exist in the fractured Unalaska Formation and corresponding plutonic bodies which are suspected to underlie most of the unaltered volcanic rocks of the northern part of Unalaska Island.As of yet,no real evidence has been found for the; existence of such systems.In fact no hydrothermal systems are known to exist in the Unalaska Formation beyond the immediate fumarole field regions of the Makushin Volcano except at Summer Bay near the community of Unalaska as shown in Figtre 1.This particular system as documented by Reeder (Ref.13)does not at present show any sub-|:stantial promise for geothermal utilization beyond a direct -use type of development. The geothermal anomaly on the southeast flank of Makushin Volcano might not be. unique for the Aleutian arc.For example,the rock groups found on Unalaska Island -can be correlated with rock groups found throughout the eastern and central Aleutian Islands;i.e.,an early series consisting of a marine volcanic and sedimentary sequence. that has been metamorphased to a greenschist grade,a middle series of plutonic rocks, and a late series consisting of an unaltered sequence of late Tertiary subaerial vol-' canic and sedimentary rocks as described by Marlow et al.(Ref.,14).In addition, the Quaternary calc-alkaline magmatism found on Unalaska Island is similar to mag- matism found within the central sections of four major arc segments as recognized by: Ray et al.(Ref.15)which make up a good part of the Aleutian arc.The large frac- ture systems caused by the convergence of the Pacific -North American plates would: also be expected near the Quaternary volcanic centers throughout the Aleutian arc, where such fractures should have strikes similar to the direction of maximum horizon-|tal compressionas determined by Nakumura (Ref.11). 4.PLAN OF ACTION _A northeast oriented zone roughly marked by fields no.1,no.2,no.3,and no.4. has been identified as possibly containing substantial hydrothermal reservoirs. Although further exploration may better define the nature of such reservoirs in the Makushin Volcano region,deep exploratory drilling along with appropriate well testing such as described by Economides et al.(Ref.16)will be required to make any estimates of the nature and the development potential of such geothermal reservoirs.It is recommended that geothermal drilling with the capability of reaching depths of 2 km be considered in this northeast target zone. If any deep geothermal drilling is to be undertaken in the Makushin Volcano region,an access road would be required to the drill site from the coast.With respect to the northeast oriented target zone,there are only three potential road. approaches:the Glacier Valley,the Makushin Valley,and the Driftwood Valley asshowninFig.5.Of these,the Glacial Valley and the Makushin Valley approaches would require,especially in the upper reaches of the Makushin Valley,the routing of the road across large 1 rs and through fairly deep'canvons.In contrast,a good part of the 16 km Drift d route as shown in Fig.5 w 4d be at higher elevations, avoiding canyons and major drainages.In this route,one bridge would be required at point A and.extensive bedrock blasting would be required at point B (Fig.5).An existing road does connect Driftwood Bay with Sugarloaf Cone.However,this road is washed out at numerous places and considerable repairs would be necessary to make it passible.An abandoned airstrip,1100 m by 35 m,is located at Driftwood Bay as shown in Figs.5 and 6.It is expected that this airfield would serve as the logistical base for any planned drilling.The surface of the airstrip is currently in poor condition but it can be upgraded to receive heavy traffic in a short period of time.The cost for building the proposed road to site C and for rebuilding the airstrip at Driftwood Bay should be under 2 million U.S.dollars,Table l. Once entering the northwest oriented target zone at site C,any further road construction would require extensive rock removal and major bridge constructions. Further surface exploration could be conducted to determine drilling targets,but logistical constraints may limit the drilling target to site C.Directional drilling| from this site could greatly extend the target region.Site C is located at an eleva- tion of about 600 meters above sea level,a site that would be engulfed a good part of the time by the famous Aleutian fog and could experience strong winds and snowfallsatanytimeoftheyear. The main emphasis suggested here for further exploration is deep drilling.Such. a recommendation should not be considered unusual especially when considering the difficulty and expenses involved in undertaking standard exploration surveys due to Aleutian weather conditions and due to the remoteness and ruggedness of the terrain. Such a recommendation is also consistent with the general exploration and reservoir assessment plan suggested by Reeder et al.(Ref.17)for site-specific investigations in Alaska. Emphasis on deep drilling should not rule out other exploratory surveys conduct ed prior to and/or during deep exploratory drilling.For example,if shallow drill: holes (i-e.,less than 200 meters in depth)could be drilled by helicopter support, 'they would be of value in obtaining temperature gradients and even rock permeability values for the Unalaska Formation and the plutonic bodies found in the region south- east of Makushin Volcano.Low temperature gradients and high permeability values would be expected for most of the unaltered volcanics on Unalaska Island,thus shallow exploratory drilling in these bodies would not be recommended. In addition,resistivity and gravity surveys would be highly recommended prior to drilling.These surveys would be geared toward defining the extent of the Unalaska|Formation and any hydrothermal reservoirs present.Passive seismic surveys which| should be conducted over a long period of time (i.e.,at least several months)could be very helpful in recognizing any magma bodies and/or reservoir.During the drilling operation,a portable seismograph should be operated near the drilling operation because of volcanic hazards. 5.DEVELOPMENT ECONOMICS Geothermal energy is "location intensive”.Hence unlike fossil fuels,there isaneedforthebenefitedmarkettobeincloseproximitywiththeresource.Unalaska.Island,with its relatively sizeable population and a large fishing and processing° industry presents an attractive target for geothermal development.A report by the, U.S.Bureau of Land Management (Ref.18)projects an electric utility demand of 50 MW. by the year 2000 under a base case.Anticipated offshore petroleum exploration in. the Bering sea will increase the demand.The same B.L.M.report projects a demand of 56. MW if moderate oil and gas leasing in the outer continental shelf proves successful.. Their projections appear on Fig.7. The present economy of the island is dependent on its harbor and the associated fishing and processing operations.More than 15 plants are located on the island, processing a variety of seafoods,dominated by king crab and salmon.In 1978 Dutch Harbor (Unalaska)was rated as the number one port by the National Marine Fisheries Service on the basis of the value of the seafood caught. The 1980 employment on Unalaska was 1600 "average w....ual full time jobs".This figure is the result of an extremely non-homogeneous employment picture with a peak of 6000 laborers during the fishing season.The B.L.M.report projects a total employment of 9000 by the year 2000 with moderate oil and gas development. At this time electric power is generated by the city and by each of the private processors.However,consolidation is likely if an attractive single power source (such as geothermal)becomes available. Table 1 presents a best estimate capital investment scenario for a 30 MW geothermal power plant on Unalaska Island.Such a geothermal power development would require a 36 km service road from Unalaska and possibly 16 more kms of road connecting the site with the abandoned military airstrip at Driftwood Bay.A similar calculation was done by Economides et al.(Ref.19)for a variety of plant sizes in increments of 10 MW. Because any new energy venture needs to be measured against existing or other possible options,a comparison between geothermal and diesel power plants of same. maximum output sizes is presented in Fig.8.While geothermal power plants of less than 30 MW appears less attractive when compared with diesel generators,they rapidly become desirable at larger plant sizes.Taking into account the Bureau of Land Manage- ment extimate of a 50 MW demand by the year 2000,geothermal development on Unalaska. appears feasible.The picture becomes even brighter when one contemplates future prices for petroleum fuels.The analysis presented by Economides et al.(Ref.19)presumed a> price for diesel that would remain constant in relation to 1981 U.S.dollars.This is however,highly optimistic,a fact that makes geothermal energy development more attrac-- tive. '6.CONCLUSION Any geothermal resources under the southeast flanks of Makushin Volcano on Unalaska -'Island might to be of the sizes and types that could be developed for electrical energyproduction.Such energy development appears to be economically attractive if the elec _ 'tric utility needs of the island exceed 30 MW. 'projection of future needs.The former point addresses the need for deep exploratory'drilling within the geothermal resource area in order to define the potenial of the The design of any output power plant must follow the resource evaluation and the| 'reservoirs.The latter point touches on significant social and economic considerations 'that need to be addressed by the local residents,and by the local and state govern- ments. '7.REFERENCES t Bull.974-B,1950,47 pp. 2.Drewes,H.,Fraser,G.D.,Snyder,G.L.,Barnett,H.G.,Jr.:"Geology of Unalaska Island and adjacent insular shelf,Aleutian Islands,Alaska”.U.S.Geological Survey,Bull.1028-S,1961,pp.583-676. 2 3,Miller,T.P.,and Smith,R.L.:"Geothermal potential of high-level magma chambers in Alaska".In:Programs and Abstracts,The Relationship of Plate Tectonics to Alaskan Geology and Resources Symposium (Anchorage,Alaska,U.S.A.:April 4-6, 1977),Alaska Geological Society,1977,p.56. 4,Reeder,J.W.:"Vapor- dominated hydrothermal manifestations on Unalaska Island, "|,Coats,R.R.:"Volcanic activity in the Aleutian Arc".U.S.Geological,Survey, and their geologic and tectonic setting”.In:Abstracts,1981 IAVCEI Symposium -.Arc Volcanism (Tokyo and Hakone,'Japan:Aug.28-Sept.9,1981),The Volcanolog- ical Society of Japan and the International Association of Volcanology and Chemistry of the Earth's Interior,1981,pp.279-298. 10. 12. 13, 15, 16, 18, Reeder,J.W.:"Hyc thermal manifestations on Unal 'a Island".Alaska Division of Geological and veophysical Surveys,Open File R_rt,In press. Motyka,R.J.,Moorman,M.A.,Liss,S.A.:"Assessment of thermal spring sites, Aleutian arc,Atka Island to Becherof Lake -Preliminary results and evaluation”. Alaska Division of Geological and Geophsysical Surveys,Open File Report,In press.- Motyka,R.J.,and Moorman,M.A.:"Reconnaissance of thermal spring sites in the Aleutian arc,Atka Island to Becherof Lake".In:Transactions,Geothermal Re- source Council 1981 Annual Meeting (Houston,Texas,U.S.A.:Oct.25-29,1981), Davis,California,U.S.A.,Geothermal Resource Council,v.5,1981,pp.111-114. Mahon,W.A.,Klyen,L.E.,and Rhode,M.:"Neutral sodium/bicarbonate/sulphate hot waters in geothermal system".Chinetsa,v.17,no.l (ser.no.64),1980,pp. 11-23. Perfect,M.R.,and Lawrence,J.R.:"Oxygen isotopic evidence for meteoric waterinteractionwiththeCaptainsBaypluton,Aleutian Islands".Earth and Planetary- -Science Letters,v.45,1979,pp 16-22. Nakamura,K.:"Volcanoes as possible indicators of tectonic stress orientation--: principle and proposal".Journal Volcanology and Geothermal Research,v.2, 1977,Pppe 1-16.. Nakamura,K.,Jacob,K.H.,and Davies,J.N.:"Volcanoes as possible indicators of tectonic stress orientation-Aleutians and Alaska”.Pageoph,v.15,1977,PP... Cameron,C.P.,and Stone,D.B.:"Outline geology of the Aleutian Islands with paleomagnetic data from Shenya and Adak islands”.University of Alaska Geophys- ical Institute,UAG R-213,1970,152 pp. Reeder,J.W.:"Initial assessment of the hydrothermal resources of the Summer Bay region on Unalaska Island,Alaska".In:Transactions,Geothermal Resource Coun-: cil 1981 Annual Meeting (Houston,Texas,U.S.A.:Oct.25-29,1981),Davis, California,U.S.A.,Geothermal Resources Council,v.5,1981,pp.123-126. Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,T.R.:"Tecton'tc history© of the central Aleutian arc”.Geological Society America,v.84,1973,pp.1555-1574. Kay,S.M.,Kay,RW.,and Citron,G.P.:"Tectonic controls of Aleutian arc:tholeitic and calc-alkaline magmatism".In:Abstracts,1981 IAVCEI Symposium|Are Volcanism (Tokyo and Hakone,Japan:Aug.28 -Sept.9,1981),The Volcano- logical Society of Japan and the International Association of Volcanology and |Chemistry of the Earth's Interior,1981,p.171. ° Economides,M.J.,Ogbe,D.O.,Miller,F.G.,and Ramey,H.J.,Jr.:"Geothermal| Steam well testing".In:55th Annual Fall Technical Conference and Exhibition of the Seciety of Petroleum Engineers of AIME (Dallas,Texas,U.S.A.:Sept.21-24,1980),SPE of AIME,SPE 9272,1980,15 pp. Reeder,J.W.,Motyka,R.J.and Wiltse,M.A.:"The State of Alaska geothermal pro-. gram".In:Transactions,Geothermal Resource Council 1980 Annual Meeting (Salt-Lake City,Utah,U.S.A.:Sept.9-11,1980),Davis,California,U.S.A.,Geothermal- Resource Council,v.4,1980,pp.823-826. United States Bureau of Land Management:"St.George Basin Petroleum Develop-_ ment Scenarios Local Socioeconomic Systems Analysis".OCS Technical Report no. 59.,1981.us , 19.Economides,M.J.,der,J.,and Markle,D.:"Unal--a geothermal development”. In:Proceedings,'uscd Annual New Zealand Geothe 1 Workshop (Auckland,New Zealand:Nov.9-11,1981),University of Auckland and the New Zealand Ministry of Works,1981,pp.7-12. Table 1.Capital Investment for a 30 MW Geothermal Power Plant, ITEM NUMBER DESCRIPTION Well 6 2,500 m,20 cm diameter (assumed 50%dry wells) Piping -1 km,20 cm diameter pipe,installed Road from Driftwood -16 km of service road,5.5 m wide,gravel, ;$125,000/km Generator 1 55 MW maximum capacity generator,installed Transformer ° Station 1 55 MW at $30/kW,installed Transmission Line 18 km of transmission line overland (helicopter installed),8 km underwater,$62,000/km Road along Transmission line 26 km of 5.5 m wide gravel road,$125,000/km Subtotal Contingency 10%of capital 'Total to be depreciated Unalaska Island COST $12,000,000 250,000 $2,000,000.$20,000,000; $1,375,000. $1,612,000. $3,250,000. $40,485,000| $4,048,700 $44,535,700- 1 ReeTE A are | 166°30' Pt.Kodin --53°45' (°)5 10 Km Fa B er in g Driftwood c grloot Coneoo Mokushin Bay Portage Bay 167° ! ;ALASKA Map Symbols ay (USA) -Fault:dashed where approximate © Fumarole field Warm and/or hot springs Recent volcanic vent pK Caldera oof X\-Map location Peony aaty ag?" .wataaerLarreapers Unaltered volcanic rocksa a? 2 (Northern part of Unataska Island)beyPlutonic rocks Unalaska Formation Figure l.Generalized geologic map of the northern part of Unalaska Island.STerTIT VTEFFeniioe uf 07s {Et aonwee .ee erasedMe ee,C +3 sit bee leg Spe 4 'y.on,Atay tal g an al as Figure 2.The main part of fumarole field no.1 as viewed looking in direction.Photograph by John W.Reeder,1980. a northeastern ate Figure 3.The main part of fumarole field no.2 as viewed looking in a southwesterndirection.Photograph by John W.Reeder,198],- TR Te omen ae Bite ag i ee!ads aoibic ' ..wererearrangeno it NT ale ee lanFigure4, Fumarole field no.6 as viewed from the air looking in a northwesterndiraotianRhatagranhhyIohnW.Reeder.19979 ' 1 omy 'a @ Fumoarole field -&Extent of large fumarole field O Warm and/or hot springs 166°S5' 54°00' 400 1 \ 3SO)o70e 400 oSwo CS°2 fs)¥S©|mMIS©cs Figure 5.Topographic map of the Makushin Volcanofumarolefields,hot and/or warm springs,and access road.drilling site Nae. region showing the location of .and a proposed deep exploratory +erymemnesFigure 6.::=. View of the Driftwood Bay airstrip taken during a landing approach fromtheBeringSea,_Photograph by Michael J.Economides and John W.Reeder,1981.s 60 F- BLM(Mean scenario), 50 ;--BaO°|w[o>]|"--BLM(Base case)-Powerdemand(MW)O|10 --- 9 LL |||| 1980 1985 1990 1995 2000 Year Figure 7.Electric utility demand for Unalaska Island from a BLM report (Ref.18). 40 -o oS vat c }a 3 - - ® a Co oO eb) -) oO am 10 -- , -.17 -----Geothermal power plant =Diesel power plant 0 rrrryrrrryrrrrytrrrryrrrr pri ir101520253035 40 Plant capacity (MW) Figure 8.Comparative economics for geothermal and diesel power plants on Unalaska Island (Ref.19). 55.97 OS oa JAY S.HAMMOND,GOVERNORr©STATE OF ALASHA [gran©)|]Fan)ANCHORAGE,ALASKA 99501 PHONE:"907-688-3555 DEPARTMENT OF NATURAL RESOURCES O PO ex oALASKA 99708 DIVISION OF GEOLOGICAL &GEOPHYSICAL SURVEYS PHONE: November 20,198] C.A.Stapleton (Mrs.) BHRA Fluid Engineering Cranfield,Bedford MK43 OAJ England Dear C.A,Stapleton: Enclosed is the paper entitled "Geological and engineering studies for geothermal development on Unalaska Island!'which |would like to present at the International Conference on Geothermal Energy which is to be held May 11-14 in Florence. The enclosed eight figures for this paper have been kept separate from the manuscript so that the publishers can assemble them on theappropriatepages.-at _ Cordially John W.Reeder Geologist Enclosures 19-128,H GEOTHERMAL PARAMETERS IN SIGNIFICANT SITES,WORLDWIDE, AND THEIR IMPLICATIONS ON THE UNALASKA DRILLING PROJECT NelPRESENTED TO THE ALASKA POWER AUTHORITY PATTI DEJONG,PROJECT MANAGER SUBMITTED BY J.A.ANSARI and M.J.ECONOMIDES UNIVERSITY OF ALASKA,FARIBANKS JANUARY 11,1981 We. ": :: e od AAWenenteINTRODUCTION Geothermal resources are found throughout the world.Some of the more important geothermal fields such as the Geysers,California;Cerro Prieto,Mexico; Lardarello,Italy and Wairakei,New Zealand;are discussed in detail in this report. | In addition,a brief but comprehensive review of the geology and tectonics of the Unalaska Geothermal Resource is presented. The Wairakei Geothermal Field (N.Z.)was found to be the one most similar to the Unalaska Geothermal Resource,both in terms of geology/tectonics and fluid behavior.A brief review of the state of knowledge of the Wairakei Field at the time of the initial drilling project and a brief history since then is also presented. WORLDWIDE GEOTHERMAL ENERGY Historically,commercial application of geothermal energy for generating Sart.oo i,OS IRelectricitydatesbackto1906inItalyandfor'the last quarter of 'a century to New Zealand.Today,geothermal power plants are generating electricity in Mexico,Iceland,Indonesia,the Philippines,Soviet Union,Japan,El Salvador, People's Republic of China and the United States (Table 1).The most intense development of geothermal energy is in Northern California,where there is a match between large resources of geothermal power and a demand for it. The world's foremost producing geothermal field is at The Geysers just north of San Francisco.Dry steam is found there in abundance and enough electricity is produced to meet the demands of a city the size of San Francisco. The current capacity of power production is expected to more than double (2,000 megawatts by 1990). The dry steam supply from The Geysers geothermal field has been so economi- cal and consistent over the years that traditionallyy cautious utility companies are confident about the reliability of this geothermal source and are now invest- ing hundreds of millions of dollars in the development of new geothermal power plants. In Southern California,where the geothermal resource is hot water,the potential is also large.There is more energy beneath the 3,000 square mile Imperial Valley in the form of compressed hot water than there is in all the oil reserves of Alaska's North Slope.It has been estimated that the commercially exploitable geothermal energy there is equivalent to the output of twenty large nuclear power plants running for over a century. TABLE 1 WORLDWIDE GEOTHERMAL ENERGY (MW) COUNTRY 1981 1985 (projected) U.S.A.932 1,900 Philippines 446 900 Italy 440 550 New Zealand 203 350 Mexico 180 650 Japan 168 650 El Salvador 95 150 Iceland 32 60 Others 19 170 TOTAL:2,515 5,380 In the Mexican part of the Imperial Valley,electricity has been generated from geothermal energy at the Cerro Prieto Power Plant since 1973.Production has been as economical and reliableyas in California,hence the Mexican govern- ment is expanding development as fast as new wells can be drilled and generating equipment can be installed. On the American side of the Imperial Valley,commercial power generation is just beginning.Production wells have been completed and several methods of generating electric power from hot waters have been tested.Preliminary agree- ments to produce electricity have been signed and many pilot plants to prove technology are now under construction or in operation. The Larderello Geothermal Field in Central Italy is a superheated steam that has produced electric power since 1906.It is producing 380 MW which makes it the second largest geothermal power production center in the world,after The Geysers. The Wairakei Geothermal Field in New Zealand is a large two-phase geothermal resource and has been producing 150 MW of electric power since 1958,and is the third largest scheme in terms of power production in the world.The 150 MW power production that has remained constant for the last decade was planned to be in- creased before the discovery of natural gas in New Zealand. In addition to power generation,geothermal energy can be used in a number of other applications such as space heating,light industries and agriculture. One of the problems associated with geoheat is the transportability factor. The unit cost of the geothermal energy delivered to the user must be competitive with other sources of energy/heat.Since the production costg at the wellhead depends,to a great degree,on the production characteristics of the geothermal field,the distribution costs within the market area are determined by a number of local factors.The long distance transmission cost is the principal variable. '. ° 1MbolerheaRRRoReee* It follows that there is a maximum distance over which the geoheat can be trans- ported and still be competitive to alternate sources of heat. Other factors which have significant influence on the cost of the geoheat delivered are: (i)Temperature (ii)Size of the market in terms of annual energy consumption (iii)Annual load factor for the system Figure 1 graphically shows how the various parameters mentioned affect the com- petitiveness of the geoheat for direct applications. LARDERELLO-MONTE AMIATA (TOSCANA,ITALY) Steam at Larderello is produced from permeable to cavernous limestone, dolomite and anhydrite of Upper Triassic to Upper Jurassic age.Field depth is controlled by a decrease in permeability with penetration into the carbonate sequence and underlying crystalline basement.The reservoir is capped by a thrust sheet comprising impermeable carbonates,argillites and aphialites of Jurassic to Eocene age.Surface leakage of steam occurs along faults extending to the carbonate anhydrite reservoir beneath the thrust plane.(Ref.1) There is no obvious source of heat in the immediate vicinity,although the presence of a deep pluton has been suggested.Tertiary granitic rocks are ex- posed on the Island of Elba about 80 km to the southwest.The closest Late Tertiary volcanics are exposed at Roccastrada. Monte Amiata consists of Pliocene and Pleistocene acidic and alkaline volcanic rocks extended through a sequence of shales,marls,limestones and sandstones similar to those at Larderello.The steam reservoir is also beneath an imper- meable thrust sheet.Past volcanic collapse is believed to have occurred,frag- ee websAAEIEAD|.19SPEIERANANS28s7fteeaie.**eSyOPTOBEN.Oe,OCPamenting the reservoir and controlling mercury mineralization and weak hot spring activity.More basic volcanic rocks occur at Radiocofari and Monte Valsini to the south. The tectonic setting of the "basement"in Larderello -Monte Amiata region has been reconstructed by Puxeddu and others (1977)(Ref.2)from the information gathered on.the possible stratigraphical position of the geological formations crossed by the wells.The following observations were made: (i)In some wells there are vertical repetitions of the same geological formations,each characterized by slight differences in the degree of metamorphism and above all,by different tecto-microfacies; (ii)In wells 68 and 152,in particular (Fig.2),intervals of overturned series can easily be recognized,thus leading to the hypothesis of folded structures.The latter are limited to one part of the well profile only and provide further evidence of strong vertical dis- harmony}; (iii)The plane corresponding to the top of the clastic Triassic and Paleozoic formations cuts across the above mentioned structures (Figs.2 &3). | Finally,the attempt at correlating the various wells (Figs.2 &4)has led to a "basement"structure characterized by overthrust planes.The latter forms the boundaries of several tectonic units with independent deformations.These units comprise rocks of the Paleozoic substratum that were folded during the pre-Alpine tectonic phases and younger formations,folded in the Alpine age only, lying with unconformity over the former.The undulating trent of the overthrust planes leads to the fact that the whole assemblage was affected by tectonic deformation after at least part of the overthrusts. 'The Halian geothermal resources consist primarily of superheated steam.As ° such,they are ideal for the generation of electricity since the fluid can be -used directly as the feed to the turbines.The composition of the geothermal fluid often contains substantial amounts of non-condensable gases (primarily co.) which must be separated from the turbine effluent.Major environmental problems are not evident in Italy,althougha continuous effort to optimize the disposal of the used geothermal fluid is underway. As in other geothermal reservoirs,the notion of reinjecting and reproducing the fluid is attractive since almost 85%of the total energy present is stored in the rock rather than the resident fluid.Yet,problems of fast breakthrough between injectors and producers have been observed.In view of potentially disastrous results,it is often preferred to reinject far away from the producers without the benefit of immediate further recovery. Much of the electricity produced in Toscana is used to power the national railroad network. THE GEYSERS The reservoir consists of highly fractured,slightly metamorphosed,sedi- mentary and igneous rocks of Cretaceous and Upper Jurassic age.The deepest wells have surpassed 2,500 metres in depth without any notable reduction in fracture permeability.Low grade metamorphic reactions,including the deposition of silica and calcite,may have contributed to a lateral decrease in permeability,but this is not clearly documented. Reservoir temperatures reach about 250°C.The heat source is apparently an igneous mass at a depth of perhaps 5 to 8 km,which has yielded a series of alkaline and acidic volcanic rocks at the surface.The age of these volcanics ae.etae:oriAMGBoaRARdoceRoeyraOrnateARIA2D,SATENEEOOSI08is believed to be Pleistocene and they cover an area of perhaps 300 to 400 km”, (Ref.3). Of the few unproductive deep boreholes,almost all encountered high temp- eratures.Permeability remains the critical variable and it is not clear whether this is controlled by local or regional fracture patterns or by mineral solution and deposition activity. The Geysers is the "other"major superheated steam reservoir in the world. All of the production (in contrast to the government owned facilities in Italy) is done by private industry.Union Geothermal is by far the largest producer in the area. While the present installed capacity of the field is just over 900 MW,a projected capacity of 1800 MW is anticipated by the middle of the decade.The maximum capacity of the field is a matter of intense speculation.Conservative estimates suggest 3000 MW,while more liberal ones propose a figure of 5000 MW or even more. Average well yield in The Geysers is 150,000 PPH while approximately 20,000 PPH are needed for each MW installed. Reinjection problems are evident here.After evaporative losses in cooling of the turbine effluent only 20%of the initial fluid is available for reinjection. High boron and ammonia content of the fluid preclude the disposal in local streams.Hence,reinjection is indicated but fear of breakthrough problems dic- tated a remote location for the reinjection well.No enhanced heat recovery is expected. The power produced at The Geysers is bought by a number of utility companies and is fed in their distribution systems. WLREeeteAFaAAADAMaBAMMraeFeBatFaReees,RMACERRO PRIETO (MEXICO) The Cerro Prieto geothermal field is located in the alluvial plain of the Mexicali Valley and is made up in part of Quaternary piedmont sediments from the Cucapah Range,and in part by deltaic sediments deposited by the meandering currents of the Colorado River.The only prominent topographic feature in the Valley is the Cerro Prieto rhyodacitic volcano,which is less than 700,000 years old. The Quaternary deposits overlay metamorphosed cenozoic sediments,which in turn are discordant on the granitic and metasedimentary Upper Cretaceous basement, Figs.5 &¢.(Ref.4). The field is located within the San Andreas tectonic system,which can be divided into different segments,the geothermal area is located along a segment that has been named Cerro Prieto (a possible prolongation of the San Jacinto fault).Some authoris have termed these segments transform faults which connect spreading centers.The evidence of these spreading centers in recent volcanic activity swarms of earthquakes,oceanic depressions and geothermal activity (Figs. 7 &8).(Ref.4). The principal fault system has a general NW-SE strike,vertical offsets either to the east or west and is parallel to such prominent faults as Imperial, Cucapah,Laguna Salada,Algodones,San Andreas,Elsinone,Banning,Mission Creek and San Jacinto (Fig.7).The faults that have been designated to the secondary volcano system,with a predominant SW-NE strike and vertical offsets to the north- west and southeast,are perpendicular to the Cerro Prieto system.The combination of these two fault systems has apparantly formed a step-faulted horst and graben topography. A geological model of the basement has been conceived based on the preceding e data.This model has been defined as a series of truncated and step-faulteda oe +0GOurayBier:tH!+eMeestatepyramidal prisms,which are elongated and strike northwest and southeast (Figs. 9&10).(Ref.4). The geothermal fluid in the Cerro Prieto area and the associated Imperial Valley field is high temperature compressed water.It is,therefore,a signifi- cantly different resource than those found in The Geysers and Toscana.The fluid temperature may reach 350°C with pressures above the corresponding satura tion pressures.The Mexicans are using the "double flash"for the evolution of steam.The method is simple,employing a separator where the geothermal fluid is allowed to expand.The reduced pressure necessarily results in some evapora- tion.The steam passes,then,through the turbines. The method,although simple,is highly inefficient.A variety of schemes are tested now to improve the energy recovery from the geothermal fluid. On the American side,Republic Geothermal and Chevron have been working with binary cycles.Instead of flashing the geothermal fluid,they are using highly volatile fluids such as isobutylene and butane in shell-and-tube heat exchanges. The geothermal fluid never comes in contact with the auxiliary fluids.Following the heat exchange,the geothermal fluid is disposed of while the auxiliary fluid turns specially designed turbines. The geothermal fluids at Cerro Prieto pose horrendous handling problems.The particulate concentration reaches,at times,200,000 parts per million.Salt content is exceedingly high with severe effects on the flow equipment.Corrosion and plugging problems are the main hindering factors in the geothermal energy production at Cerro Prieto. 8APR...PNAaon,Beecor.OMereoeroe+otOOaPsS.APt+aORTP,.POPES,RNPOSITPE,PTWALRAKEE (NEW ZEALAND) _.«The Wairakei Geothermal Field is underlain by nearly horizontal,Quaternary, volcanic and clastic rock sequence and is situated in the Central Volcanic Region POeeeieeeLeof the North Island of New Zealand.Within this region,near the Wairakei field, are two main structural features:a belt of active normal faulting called the Taupo Fault Belt,and a major structural depression,known as the Taupo Basin. Both of these structural features are believed to be associated with the divergent boundaries of the Australian and the Indian plates.The field,as defined by resistivity measurements and the main production borefield lies across a zone at the junction of these structural features (Fig.11).(Ref.5). The Taupo Volcanic depression extends for over 200 km in a north-northeasterly direction,parallel to the main structural grain and culminates in the north at the active volcano White Island,in the Bay of Plenty.The zone is some 25-30 km broad at its widest.Fumargles and hot springs are abundant in the central 100 km long portion of the depression.Mud volcanos and ground subsidence are also associated with the Wairakei geothermal field.(Ref.6). Power production commenced in 1958 with a 69 MW plant. The scheme was to tap a vast underground water system heated by perhaps molter rocks at depth. About 100 wells have been drilled in the area of which sixty-one are commercially attractive,a ratio that is the best in the world. The fluid production in the reservoir has been declining so in order to assume continuous power output at installed level,new wells are drilled and the inlet pressure at the turbines has been reduced from 13.5 bars +7.5 bars. | About 80%(by weight)of the discharge from the wells is hot water.Separa- tors at the wellhead remove the liquid water and the remaining dry steam is piped to the turbines.The hot water from some of the high pressure separators is reflashed at a lower pressure.Three batteries of turbines are employed: High pressure (H.P.),intermediate pressure (I,P.)and low pressure (L.P.).The iL latter use an inlet pressure of 2 bar with an outlet pressure of barely 1.03 bar . '"absolute.The effluent from the power plant is discharged into the Wairakei stream.No environmental effects from the discharge have been observed.The particulate composition of the discharge is lower than the adjoining streams. The electricity is fed at 200,000 volts into the North Island grid system. GEOTHERMAL RESOURCES ON UNALASKA ISLAND The Unalaska Formation constitutes the oldest and most extensive group of the rocks in the island and consists of thick sequence of coarse and fine sedi- mentary and pyroclastic sediments intercollated with dacitic,andesitic and basaltic flows and sills,cut by numerous dikes and small plutons.(Ref.7). The Unalaska Formation is exposed over two-thirds of the island and is be- lieved to be early to mid-miocene in age and has been extensively folded,faulted and intruded by the plutonic rocks with moderate hydrothermal alterations occuring near the plutons. The batholiths and smaller plutons are granodiorite with border phases as mafic as gabbro.The plutonic rocks are thought to be the products of crystalli- zation of a granodiorite magma that invaded the rocks of the Unalaska Formation by assimilation,stoping and forceful intrusion.The age of the pluton is con- sidered to be younger than the early miocene and older than the middle pleistocene times. | The Unalaska Formation in turn is unconformably overlain by the Makushin Volcanics,which are comprised of basalt and andesite flows and pyroclastic rocks.(Ref.8). 7” The Makushin Volcanics constitute most of the Makushin Volcano,a broad volcanic dome more than 1,800 metres high and 16 kilometres wide.The thickness of the Makushin Volcanics varies greatly,but probably does not exceed 1,500 metres.The Makushin Volcanics are believed to be middle to late pleistocene. Much of the basalt and andesite is highly glaciated and must precede at least part of the late pleistocene time. Late Wisconsin to Recent volcanic cones and lava flows are scattered about the base of Makushin Volcano and have been collectively mapped as Eider Point Basalt.(Ref.7).The volcanic rocks rest unconformably on glaciated rocks of the Makushin Volcanics and the Unalaska Formation. A series of recent cinder cones and craters lie along a westward-trending fissure extending from the Makushin Caldera to Point Kadin.The volcanic vents probably reflect the intrusion of the magma into the fissure at shallow depths. The Makushin Volcano is still active and-is known to have erupted at least 14 times since 1760,with a minor eruption occuring in 1980.(Ref.8).The Island has been intensely glaciated and glacial landforms are prominent everywhere.The mountains contain U-shaped valleys,cirques,aretes and icecovered features of every size.An ice field of 40 ton caps the Makushin Volcano with glaciers descending as low as 210 metres.Till from the latest Wisconsin ice advance occurs in the lower cirques and valleys.More recent,fresh-looking moranies, located near existing glaciers,indicate small advances and recessions have taken place perhaps within the last few hundred years.(Ref.7). Faults,joints and related linear features are abundant,but the length, direction and amount of displacement so far have not been determined with the exception of a few.Most of the faults are nearly vertical and the strong topographic alignment of Beaver Inlet and Makushin Bay,which nearly bisects the Island,suggests a major fault.(Ref.8). A statistical analysis of linear topographic features from areal photographs performed by Drewes and others (1961)(Ref...7)showed a dominantly northwest ,SEAaSFrRR=BeNeeFRAPRTS.OAASSsSetrend in the Unalaska Formation in the more altered rocks near and in the batholiths, and a strong pattern of north and east trending sets of linear features in the less altered rocks away from the batholiths. Unalaska Island is part of the Aleutian arc that comprises the entire chain of the Aleutian Island and its 'structural extensions -the Alaska Peninsula and the Aleutian Range.Over 76 major volcanos occur along this arcuate belt,ex- tending over 2,400 km from Mt.Spurr on the east to Buldir Island on the west. Of these,at least 36 have been reported active since 1760 and the Makushin Volcano is one of these active volcanos with the last erruption in 1980. This chain of active volcanos lies immediately north of the Aleutian Trench, a convergent boundary between the North American and the Pacific lithospheric plates.This convergence produces one of the world's most seismically active belts.Much of the seismicity originates from the Benioff Zone,the subcrustal region where the Pacific plate is being actively subducted under the margins of the North American plate along the Aleutian Trench.And with the exception of the Amak and Bogoslof Islands,the Aleutian volcanos all lie about 100 km above the Benioff Zone.In addition to this,the erruption of the Aleutian magmas appears to be intimately related to the subduction process. The Unalaska Island,which is an island arc,should have extensive folding, thrust and vertical faulting and metamorphism associated with active volcanism magmatic intrusions. Several thermally active areas have been identified on northern Unalaska Island and all but one are believed to be associated with the Makushin Volcano. Fig.12 (Ref.9)and Fig.13 (Ref.8). The fumarole fields and hot springs associated with the Makushin Volcano occur in the Unalaska Formation and in the plutonic rocks that have intruded it. (Ref.9).All these showings have been classified in the following three groups coteonpeemerented +Fn1A.-MaeoteRReetoefeBee'son the basis of geographic location; (i)Glacier Valley (ii)Makushin Valley (iii)Summer Bay A complete and fairly comprehensive geologic and engineering evaluation of these sites has been presented by Reader and Economides (Ref.9).Geochemistry of the thermal waters of the Unalaska Island has been presented by Motyka and others (Ref.8).aLbaahy oeaTeoRODB®BDtsiaer2MNiPRADteEBTERPaBEonespedSITE MOST SIMILAR TO THE UNALASKA GEOTHERMAL RESOURCE IN THE VICINITY OF THE MAKUSHIN VOLCANO The Wairakei Geothermal Field (N.Z.)appears to be the one most similar to the Unalaska Geothermal Resource in the vicinity of the Makushin Volcano. Like Unalaska,active volcanic and seismic activity is associated with the Wairakei Geothermal Field.Both the volcanic and seismic activities at the Wairakei Geothermal Field and the Unalaska Geothermal Resource are associated with the movement of the lithospheric plates.The only difference being that the Wairakei field is associated with the divergent boundaries of the Australian and the Indian plates and Unalaska Resource is associated with the convergent boun- daries of the Pacific and the North American plates. In the Unalaska geothermal sites,there are no mud volcanos as those associated with the Wairakei field because of the absence of any mudstones above the geothermal reservoirs.This is both advantageous from the point of view of stability of the area and disadvantageous because nothing may stop the surface water from perculating down into the reservoir and cooling it down.However, there is no evidence that confirms or negates the hypothesis of surface waters making it down to the geothermal reservoir in Unalaska.The subject needs further study. The chemistry of the waters is similar while the reservoir temperature is expected to be close. | E ha ttAseSROPPRRRRS3BtaOeestaPRLSeeihSadPARatoatePoEBARRASTATE OF KNOWLEDGE OF THE WAIRAKEI GEOTHERMAL RESOURCE AT THE TIME OF INITIATION OF THE ASSOCIATED DRILLING PROJECT At the time of putting the wildcat,a comprehensive geologic map of the Wairakei geothermal area was available.All the faults were plotted and the movement along them recorded.All the major fracture sets were recognized and recorded.Movement of the surface water was fully known and it was believed that some mixing of hydrothermal fluids and meteonic water is taking place at shallow depths above the lacustrine mudstone. The system was believed to be liquid dominated with some localized vapor dominated zones.The reservoir temperatures were believed to be in excess of 250°C.Mud volcanos existed before exploitation commenced,but the ground sub- sidence due to decreasing pressures was not anticipated. Before exploitation,the Wairakei Geothermal Field was liquid-dominated, with a near-hydrostatic pressure gradient.Water,at 260°C,flowed up fissures and intersected the boiling point curve at about 500 m depth.Saturation condi- tions controlled aquifer temperatures at shallower depths (Ref.10).Above 100 to 200 m depth,the hydrothermal fluid mixed with cold meteoric water in super- ficial pumice deposits.However,the underlying lacustrine mudstones of the Huka Formation prevented infiltration of surface waters to greater-depth.Hot alkali- chloride water from the deep system emerged in topographic lows (e.g.Geyser Valley,Lower Waiora Valley,and along the Waikota River),whereas the separated steam tended to emerge in topographic (and structural)highs (e.g.the Upper Waiora and Karapiti thermal areas.)A small vapour-dominated zone,along the jointed upper surface of a rhyolite sill in the south-west of the Field,may have fed the impressive fumarole ("Karapiti Blowhole")in the Karapiti Thermal Area.(Ref.11). [A When exploitation began in 1951,the natural heat flow from the Field was Fe,SEI6RD,POCDOD,430 MW.Heat extracted through wells in the production borefield exceeded the natural heat flow in 1955,and increased to a maximum of 2800 MW during 1964. It has subsequently declined to about 1650 MW today. Large changes in the natural heat flow have occurred as a result of this exploitation.Drawdown in the hydrothermal aquifer caused the liquid outflows in Geyser Valley to decline,and an enlarging,vapour-dominated zone formed at the top of the acquifer immediately beneath the Huka Formation.Most steam- heated thermal areas across the Field increased in heat output due to the in- creased mobility of steam at the top of the aquifer.These increases outweighed the effects of declining geyser and hot spring activity in Geyser Valley,and the total natural heat flow increased,Fig.14 (Ref.10).A spectacular increase took place in the Karapiti thermal area,where numerous hydrothermal eruptions caused large craters,often containing very active mudpools or fumaroles.In the mid-1960's the natural heat flow passed through a maximum of almost 800 MW - about twice the pre-exploitation figure.The heat flow has subsequently declined to 600 150 MW. By the early 1960's the decline in aquifer pressure had become sufficiently large to stimulate a four-fold increase in the flow of hot water from depth. The rate of fall of aquifer pressure then began to decrease,and hence the draw from thermal and mass storage of the upper part of the aquifer also began to decrease.During the 1970's,aquifer pressure almost stabilized,suggesting that the mass outflow from the Field is now almost completely compensated for by mass inflow from depth.However,the extensive vapour-dominated zone generated during the first 10-15 years of exploitation has become an important factor in- fluencing the subsequent thermal behaviour of the Field.As outputs of the production wells gradually declined with the fall in aquifer pressure and temp- erature,the increased steam flow from thermal areas became a significant fraction ..be Ma?7aATARIBare,MeASAERAAFVRMsBeteeVemeweaMeeeteoFaggBaertis-eneABSRBoEMAPR?9RITRFD«nof the total heat flow from the Field.In addition to the natural steam loss, some of the shallower wells also began to draw directly from the vapour-dominated zone,and have contributed to its decline in pressure.This has induced further boiling and aquifer temperatures have continued to fall. Infiltration of cold water into the hydrothermal aquifer may be causing deterioration of the Field on the northwest side of the production borefield. Over the last decade,a 1 km area between the borefield and Geyser Valley has become noted for sharp falls in enthalpy and chloride content of some wells,and almost complete cessation of surface thermal activity.Faults which were acting as conduits for hot chloride water emerging at Geyser Valley may now be permitting a downward flow of surface meteoric water. The history of drilling and exploitation at the Wairakei field is expected to be duplicated on Unalaska Island if a large reservoir is identified through the present effort by the State of Alaska.The experience of other geothermal sites in the world will greater enhance the possibility of success in the Unalaska venture.oNeerena MP s -. 4 t: a sOCRArILEOFAEREOATFOERAYBAFBh10. ll. REFERENCES Kruger,P.&Carel,0.;"Geothermal Energy,Resources,Production, Stimulation",Stanford University Press,Stanford,California,1981,page 27. , Puxeddu,M.&Squarci,P.,Rau,A.&Tongiorgi,M.and Burgassi,P.D.: "Stratigraphic and Tectonic Study of Larderello -Travale Basement Rocks and Its Geothermal Implications",Geothermics,-Vol.6,page 83-93,Pergamon Press,Great Britain,1977. Kruger,P.&Carel,0.:"Geothermal Energy,Resources,Production, Stimulation",Stanford University Press,Stanford,California,1981,page 32.' Puente C.,I.&De La Pena L.,A.:"Geology of the Cerro Prieto Geothermal Field",Geothermics,Vol.8,page 155-175,Pergamon Press,Great Britain, 1979. Hunt,T.M.:"Rechange of Water in Wairakei Geothermal Field Determined From Repeat Gravity Measurements",New Zealand Journal of Geology and Geophysics,Vol.20,No.2 (1977),page 303-317. Hunt,T.M.&Latter,J.H.:"Seismic Activity Near Wairakei Geothermal Field,New Zealand",proceedings of The New Zealand Geothermal Workshop - 1979,page 14-19. Drewes,H.,Fraser,G.D.,Snyder,G.L.and Barnett,H.F.,Jr.:"Geology of the Unalaska Island and adjacent insular shelf,Aleutian Islands,Alaska", U.S.G.S.Open-File Report 1028-S,1961,page 583-676. Motyka,R.J.,Moorman,M.A.&Liss,S.A.:"Assessment of Thermal Springs Sites Aleutian Arc,Atka Island to Becherof Lake ---Preliminary Results and Evaluation",Alaska Open-File Report,D.G.G.S.,University of Alaska, Fairbanks,1981. Reeder,J.W.,Economides,M.J.and Markle,D.R.:"Geological and Engineering Studies for Geothermal Development on Unalaska Island",To be presented in Florence,Italy in May,1982. Tompson,G.E.K.:"Temperature gradient within and adjacent to the Taupo Volcanic Zone",New Zealand Journal of Geology and Geophysics,1980,Vol.23, page 407-412. Allis,R.G.:"Changes in Heat Flow of Wairakei Geothermal Field",proceed- ings of,The New Zealand Geothermal Workshop,1979,page ll. WO.etFPaTeso&ah5,CRAMehTRlsAoOeCMTSTAASey$3TDieselof$/8BL.aoqTaiGeothermalheatmiliskWhBunkerot$/88L.aTPytAY, ae -Uy'Distribution Y4rCosts4 ol ak WL 2e Eroguction RY SSosts ou ou °i ESS RSS to 20 30 40 30 Transmission,km Figure 1 -Total cost of geothermal energy in relation to tne transmission distance. Figure 2 -Cross Section in Larderello-Castelnuovo Area. Explanation of symbols:(1)Liqurid nappes (Upper Jurassic to Eocene);(2)"macigno" flysch of Tuscan nappe (Oligocene to Miocene);(3)Triassic evaporites of Tuscan nappe;(4)Triassic quartzites and phyllites;(5)Triassic quartz pebble conglom- erates;(6)porphyroids and porphyric schists (Permian or Carboniferous);(7)Paleozoic quartzites and phyllites;(8)Paleozoic feldspatic quartzites and phyllites;(9) Paleozoic quartzites micaschists;(10)marble (unknown age);(11)magnesian limestones (unknown age);(12)tectonic contacts. et,Cee.,eeca*AaAAOPSETPeeHtPOMMTaTAweheFigure 3 -Buried geological features of the top of the "basement"in Larderello- Castelnuovo area.(1)and (2)Triassic clastic rocks and Paleozoic rocks of the Upper unit,respectively;(3)Triassic clastic rocks of the Lower units;(4)overthrust;(5)stratigraphic contact;(6)isobaths. AOrAofGE,AW.%2.21d8AAAMieeeADVTcasteunvars ° LARDUTLLD BOCCHE BEANOSeamaz2iagGICCIOUETA a eBStrorennce woth geame A Catt oveve D teoeme A Figure 4.Correlation of some well profiles in Tuscany geothermal region. Explanation of symbols:(1)tectonic surfaces;(2)stratigraphic unconformities; (3)Liquid nappes (Upper Jurassic to Eocene);(4)"macigno"flysch of the Tuscan nappe (Oligocene-Miocene);(5)Triassic evaporites of the Tuscan nappe and evaporitic intercalations within Paleozoic quartzites and phyllites;(6)Triassic quartzites and phyllites;(7)Triassic quartz pebble conglomerates;(8)porphyroids and prophyric schists (Permian or Carboniferous);(9)Paleozoic quartzites and phyllites;(10)Paleozoic feldspatic quartzites and phyllites;(11)Paleozoic quartzitic micaschists;(12)the same as (11)but affected by contact metamorphism; (13)marble (Paleozoic or unknown age:in Niccioleta area metasomatic replaced by skarn). OMA ssposuiTraQONCGATIVa | PALLas INPTERIO4 POR Stmasca RAVETWAL 5 }LR saa neremos Pon |HOMROEENgee was Quiros eta ecN | SIMBOLOS - le Aluvion Oepesttos Fiuvssies Cactermerio Voleo ns LaeMerinoimPlioceneJ Gronttoe y Genogeritics Crotacice Tongtitos i iyCompeyohawtomortice Poreosrce Figure 5 -Geologic Map of the Cerro Prieto Area B ABAMCOS ALUVIALES SE CuCaram OE TOrCEN o-r< GaamiTICO Y METASEDWENTARIO RECIENTE ROCAS RiOOACITICAS °o o ' z <|uw <| DEPOSITOS NO CCNSOLIDADOS CONSTITUIDGS POR -o e <ARCILLAS,ARENAS Y GRavas;CON ESPESORES wa -WwW :DE 600 A 2500 =o @.-! -eo t .<: A .2°ld > : © .ao |° :.'e ° ::|DSCORDANCIA,CAMBIO DE FACIES ,0 CONTACTOPORMETAMORES-ra.Soooé. '=N °4 €<° :1S) c LUTITAS DE COLOR CAFE CLARO CAMe:aN00 °=» :&PROFUNDIDAD &COLORES GAIS CLARO Y CRS -z 'OSCURO,INTERESTRATHICADAS CON ARENISCAS &Ww e DE COLOR GRIS CLARO,CONSTITUIOAS OC FRAG <ad Wi 3 a;MEMTOS O€CUARZO Y FELCESPaTOS CEMEN-eo 4 TADOS INOISTINTAMENTE CON CARBONATOS ¥5 oO =[o)tLIGE.SU ESPESOR ES 2000 =.aProxw.'stu ES DE 2 -a = ' ? 3 4 Og;< a eo Oo eo ;ROCAS IGNEAS Y METAMORFICAS CONSTITUI-o roDASPORGRANITO,GRAMODIORITAS,GNEISSES <x &N =::Y EsQurstos.Ww s 8 ij :cz 3 ud c o = . €vereFigure 6 -Generalized Stratigraphic Column of the Cerro Prieto Area.AMAeyteeayratofasto) im.osBT: P©. é© :+SBIweeaRhBR.AUFFP,vaPRw-omeeweeeew=nN wee Noeeeeeee nino ¢ ---2F ALLA e EPICENTRO CE TEMSLD RES (Ente Sy *EY sates4e°Siaoe escaio ce ne 4 ZONA GEOTERMICA NN ric LINEA OrVvisorta ]50 .100 km ee rae ae .Pan "se NosSake,NN NS ar x\N on 'Ea -x G OL FO ie a €o\,rOo ALIFORWIAs Figure 7 -Regional Tectonic Map SyesaedesReAEneEGYeea s Fs voCoB.STApyaenPULAALAGESPANSIEROBad08ABgOBee> a ;Fatta ade San Anarde Foils de Laguna Salada £9 Laese Searecmecee )Lonse Ptegedes \:Sossre te Jesereae BL vreda Jeven{Presstecese} 9 3 so Ku CALIFORNDN "' |. LOCALIZACION B Figure 8-A.transform fault and spreading center model B.location of these faults and centers in the Imperial and Mexicali Valleys.Zonas plegadas:folded zones. * « a' :POPFSBeReOPUSTegFLEUR+RWeeeeArrPaseReanCRTeFigure 9 -Basement Configuration specvorewaneareede ”Sh i ie "™ a wwe FG Pn ren ce Ce RL ALOE,IEE,ED SS.OO.POTTY aa ..: ew :corsre do @CerroPrietoSlerraCucapaMexicoll-- a XS eee FEI EVPOLPATARA=>Rs =i;wed Seman Ayy"yyaanCLAROPRIETO n” °o « ro Ld 2 : a < a a Zz 2 cy °o « a BaecomPrnre sion -{ Sedimeates ODOeltetecos ae Consetideadeos (Arcittos,Arenes y Groves) Zone da Lee Sedimentes Consotldados Sumemente Freacturade 4 Sedimentes Oeltetces Conselidedes (tutites,Limetites y Areniscos) HKece Grenitice y Metecscedimentaria ; ' . 0 5 10 kin Sedimentos de Pledemeonte (Abonices Aluviates)L i !wens -__.on |. j ' Figure 10 -SW-NE Geologic Cross-Section z3ba eeeMPssNateBLTsTMTPRPATEARaehe7 7 Ae 7 ,, /"0 at.1.ya §kmN/&KaYo©S/=A "ra4..."Yt /Q eX "eS7pat&tS/- |,S ie7See./es @ee av Boundary of the geothermal fietd ue 7 . . /Wairakei =: Lake Taupo Figure 11 -Location and extent of Wairakei Geothermal Field.Broken lines indicate the approximate locations of the boundaries of major structural features. The zone of stippling indicates the boundary of the field and corresponds to the zone between the apparent resistivity contours of 10 and 20 Qn. Triangles indicate the locations of seismographs used in this survey: portable instruments are indicated by open triangles and permanent in- struments by solid triangles. ee SoMieratte,PELIIOAR,WDOOaekAOAM,UnieanTOUPPeMER4 EE E ; ; oO NORTH. OU Pt.Kadina +-§3°45° 'i5QO510Km° ' LUT LT AL Pa Sea 166°30 Bering 54°...* ve .7 Table Top:--Ne Mtn quienesONL74&wide Bay Cone Unatoska Boy aca|tt 8 7augutoot Cone.SOR Mokushin Bay sori Portoge Gay ----Fault:dashed where approximate Map Symbols Fumarole field Warm and/or hot springs Recent volcanic vent ae . Caldera ;oF X\-Map location : . .(Northern part of Unaltered volcanic rocks ;Unalaska Itstand) Plutonic rocks Unalaska Farmation Figure 12 -Geothermal Site Locations eeomeeeSA"8224+Tyee:.. i :E Gratn fhew 3 &.Syblimates \\/||"4!8C=560-f Qe ,of )Soil.46°-/;*P , "tawgete ;eae *\\:|aeop\i ;Soe ts \2 Springs:To :ron 'Drainage ° S 8RD _- Seeps OSteam 'Vents Dry(Old Spring °Location). Snowficld,:3 o nowfield,.ED August 1980 0 50 100 150 200 l i !1 _3 Feet . 0 10 20 #30 46 650 t l 1 t !} Meters Seeps All Temperaturee in °C &66°All Flows-in liters/minute of,89-7 Multiple.Sources pees -a17.3°;__|°Olde Sviteaheer ---|25.4¢ To Glacier River %7 . a .y . All Conductivities in pmhos/em. o ..Figure 13 -Detail at Glacier Valley Hot Springs on Unalaska Island. oen,eeteFPSOsSeeeooRRPavesFone007 ,ce TOTAL HEAT FLOW 760+ 600F-a Heat 2Oor . FLOW (MW)L00- THERMAL 300+ 200 = oS _-HOT_WATmoarFLO o19501960"07 4930 YEARS Figure 14 -Surface heat flow changes at Wairakei since 1950.The total heat flow has been split into two components:that from hot water flows (seeps and springs),and that from areal heat losses (thermal ground,pools) and specific steam flows.