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Development Potential of the Makushin Geothermal Reservoir 1985 2
_Denig-Chakroff and others COST OF OPTIMUM POWER PLANS 77.8 (Millions)a]o(=)NETPRESENTVALUE7 T LOW MODERATE GROWTH SCENARIOVAdieselbinaryRed «total flow Figure 4.Graph showing the net present value of optimum power system plans for three growth scenarios. COST/COST RATIOS -68 3 1.25 YY DIESELCOST/GEOTHERMALCOSTNS\0.1 - 0 wW MODERATE HIGH GROWTH SCENARIO binary total flow Figure 5.Graph showing the cost/cost ratios of diesel power system plans to geothermal power system plans for three growth scenarios. Denig-Chakroff and others thermal system also proved more economical than diesel systems for each growth scenario. A sensitivity analysis was conducted to determine the effect of a 4.5%discount rate and various diesel fuel escalation rates on the economics of the alternative power systems.The lowest fuel escalation rate analyzed representeda4%(real)annual decrease in the price of diesel fuel until 1988 and a constant fuel price from 1988 until the end of the period of economic analysis.Even with this low fuel escalation rate and a 4.5%discount rate,the total flow geothermal system was slightly more economical than a diesel system for the moderate growth scenario.For the ow'growth'scenario, geothermal systems were not economical at the low fuel escalation rate but were the most economic source of power with a 4.5%discount rate at medium and high fuel escalation rates. CONCLUSIONS Although this is a _preliminary economicanalysis,some general conclusions can be drawn from the results.It appears that a geothermal power system may be competitive with a diesel power system on Unalaska Island.Major factors contributing to the economic feasibility of a geothermal system are the characteristics of the resource,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 andothers,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 geo- thermal 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 genera- tion on Unalaska Island,concentrating on load projections and market conditions in the communi- ty of Unalaska/Dutch Harbor. ACKNOWLEDGMENTS The authors wish to extend a sincere expres- Sion 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 sup- port. REFERENCES Dames and Moore,1982.Aleutian regional air- port,project documentation.Report for the City of Unalaska,p.44-45. Denig-Chakroff,D.N.,1985.Unalaska/Dutch Har- bor reconnaissance study findings and rec- ommendations.Report for the Alaska Power Authority. 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 Geo- thermal Reservoir Engineering,SGP-TR-84, Stanford University,Stanford,Ca.,in press. Morrison-Knudson Company,Inc.,1981.Geo- thermal potential in the Aleutians:Un- alaska.Report for the Alaska Division of Energy and Power Development,p.2-5. Reeder,J.W.,Denig-Chakroff,D.,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,Hawaii,in press. Republic Geothermal,Inc.,1983.Unalaska geo- thermal project,phase IB final report. Report for the Alaska Power Authority con- tract CC-08-2334,v.1,p.2. Republic Geothermal,Inc.,1984a.The Unalaska geothermal exploration project,phase II final report.Report for the Alaska Power Authority,contract CC-08-2334,p.X19- X25. Republic Geothermal,Inc.,1984b.The Unalaska geothermal exploration project,executive final report.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. Report for the Alaska Power Authority, contract CC-08-2334,p.48-51. DEVELOPMENT POTENTIAL OF THE MAKUSHIN GEOTHERMAL RESERVOIR OF UNALASKA ISLAND,ALASKA David Denig-Chakroff(2)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 to determine the potential for developing the 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 lowest possible cost to the consumer and to encourage the'long-term economic growth of the state. One objective of this paper is to summar- ize 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. cues UNALASKA ISLANDVALLEY dK ease came @ THEAMAL GRADIENT HOLES >GEOTHERMAL RESOURCE WELL 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;land 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 resourceencountered.Phase III activities includedcontinuedandmoreextensivetestingofthe 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 temperatures of up to 383°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 conclud- 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 ofIse)4,000 feet (Republic Geothermal,Inc.,983). Phase II of the exploration program was initiated in the Spring of 1983.The exploratorywellwasstartedinearlyJune.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 a bottomhole pressure of 478 psi (RepublicGeothermal,Inc.,198442).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 and others,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 productive geothermal reservoir (Economides and others,1985).Sustained flow of 63,000 JIb/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 well at the site should be capable of flow rates of 1.25 to 2 million 1b/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 west of the City of Unalaska in a remote,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_e 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 serious 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 small 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 COST/COST RATIO DIESEL VS TOTAL FLOW SYSTEM 2.1 2.0 - 1.9 + 1.8 - 1.7 4 1.6 - 1.5 - 1.4 -C/rCRATIO1.3 - 1.2 - 1.17 1.0 |oe0.9 q LJ q ' 2.1 4.2 6.3 8.4 10.5 12.6 NET GEOTHERMAL CAPACITY (MW) o 2%scenario +4%scenario °11%scenario DIESEL VS BINARY SYSTEM c/'CRATIOar*)!0.7 :1 3.35 6.70 10.05 13.40 NET GEOTHERMAL CAPACITY (MW)ie]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 economic analysis,some general conclusions can be drawn from the results.It appears that a geothermal power system may be competitive with a diesel power system on Unalaska Island.Major factors contributing to the economic feasibility of a geothermal system are the characteristics of the resource,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 flow tests and reservoir analyses (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.,ODenig-Chakroff,D.,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,Hawaii,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 II final report for the Alaska Power Authority,contract CC-08-2334,p.X19- 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. Denig-Chakroff and others A diesel power system plan was developed as the "base case"to compare the geothermal power system plans under consideration.A diesel generator capacity addition/replacement schedule was devised such that the needs projected in the electric load forecasts would be met even with the largest power unit down for maintenance.The replacement schedule was based on an assumptionthatdieselgeneratorshavea20-year usefullife.A separate diesel power system plan wasdevelopedforeachofthethreegrowthscenarios. UNALASKA/DUTCH HARBOR TOTAL LOAD FORECAST 11%growth scenario Qawneyr)(Thousanas)ENERGYUSE4%growth scenario 2%growth scenario Figure 2.Graph showing the total electric load forecast for Unalaska/Dutch Harbor from 1985 to 2025. The geothermal power system plans were developed by assuming that one or more geothermal units would come on line in 1990.Geothermal units were based on net MW deliverable to the power grid after making deductions necessary to supply station service.Ten geothermal powerplanswereanalyzedforeachofthethreegrowth 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,whichever was less.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 were taken from Republic Geothermal,Inc.(1984c)and modified to reflect a 20%contingency factor. Construction of a 34.5 kv transmission line 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 maintenance costs were assigned constant values'of$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 is 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%growthscenario,the optimum total flow system is4.2 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 systemsareclearlymoreeconomicalthanthediesel 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 2%AND 4%GROWTH SCENARIOS Cy(Millions)gi.NETPRESENTWORTHWGZZ]diesel binary EEX]total flow 41X GROWTH SCENARIO 210 +4200|G RETPRESENTWORTH(Millions)76141%scenario ZZ]diecet binary (EEE)total flew Figure 3.Graphs showing the net present worth of optimum power system plans for three growth scenarios. Denig-Chakroff and others vices.Figure 3 illustrates the total elec- tric demand forecast for each growth scenario. HISTORIC T PORECAST POPULATION(Thoueande)r°i2.0 +1.0 f{0.0 TrTTTrrrrrrytrrrrrr:r TOT TTTee196519701975198619851990199520002005 YEAR Oo LOW GROWTH +MODERATE GROWTH °o HIGH GROWTH Figure 2,Historic and forecast trends,1965 -2005 1985). population(Denig-Chakroff, HIGH GROWTH SCENARIO MODERATE GROWTH SCENARIO LOW GROWTH SCENARIOCOINCIDENTPEAK(MW)v T 1965 1900 1905 2000 20035 Figure 3.Graph showing the total electric demand forecast for Unataska/Dutch Harbor from 1985 to 2005 (Denig-Chakroff,1985). A diesel power system plan was developed as the "base case"to compare the geothermal power system plans under consideration.A diesel generator capacity addition/replacement schedule was devised such that the needs projected in the electric load forecasts would be met even with the largest power unit down for maintenance.The replacement schedule was based on an assumption that diesel generators have a 20-year useful life.A separate diesel power system plan was developed for each of the three growth scenarios. The geothermal power system plans were de- veloped by assuming that one or more geothermal units would come on line in 1990.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 geothermalsystem,whichever was less.The remaining energy demand would be met with backup diesel generators. The net present value of each power system plan was calculated using a 3.5%annual dis- count rate.Geothermal system construction costs were taken from Republic Geothermal,Inc.(1984c)and modified to reflect a 20%contin- gency factor.Construction of a 34.5 kv trans- mission line and a road to the geothermal site were estimated at $15.473 million,including a 30%contingency factor.Diesel fuel priceswereassumedtodecreaseby4%(real)in 1986, to remain constant between 1986 and 1988,and then to escalate at 2%per year until 2005. Fuel costs were based on a production of 12 kilowatt-hours per gallon of fuel.Diesel generator cost and salvage value were estimat-ed at $700 per kilowatt of installed capacity. Annual operation and maintenance costs wereassignedconstantvaluesof$1.012 million for the "base case"diesel system and $1.275 million for the geothermal systems. RESULTS The net present value was calculated for each power system plan.The optimum diesel, binary geothermal,and total flow geothermalsystems(i.e.,those with the lowest netpresentvalues)are depicted in Figure 4.The optimum geothermal systems for the low and moderate growth scenarios are a single-unit(3.35 MW)binary system and a 2-unit (4.2 MW) total flow system.The optimum systems for thehighgrowthscenarioarea3-unit (10.05 MW)binary system and a 5-unit (10.5 MW)total flow system.Optimum geothermal system plans were compared to the optimum diesel system plan for each growth scenario using a cost-to-cost ratio(Figure 5).The analysis shows that the geothermal systems considered are more econom-ical than diesel generation for each growth scenario.The most economical source of power based on this analysis was the total flow geothermal system which showed a 1.10 cost/costratiowithacomparabledieselsystemforthelowgrowthscenarioand1.25 and 1.68 ratiosforthemoderateandhighgrowthscenarios respectively.Although the construction costestimatesusedforthebinarygeothermal systems were considerably higher than those used for the total flow systems,a binary geo- 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 onthevalueofitslandedcatch(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 serious slump in the fish-processing industry,the population has been estimated at about 1,500 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 oi]devel- opment.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 a preliminary look at the economics of de- veloping a geothermal power facility on Unalaska Island.Prior to design and construction,a more detailed feasibility study would be re- quired. This analysis used present value 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 value in 1985 of each geother- mal power plan is compared to the net present value 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 jis 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 small 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 low growth scenario for the planning period.A moderate growth scena- rio based on a 4%annual population increase was analyzed as a reasonable expectation of growth.A high growth scenario was considered, based on an 11%annual population increaseprojectedbyDamesandMoore(1982)assuming a low level of bottomfish harvest and processing on the island.These three growth scenarios are depicted in Figure 2 as they compare to historic population trends. For each growth scenario,electric load fore- casts were developed for residential,commer- cial,and industrial users and for city ser- Denig-Chakroff and others City of Unalaska (Figure 1).The appropriation was preceded by a number of geologic investiga- tions 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;land 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 resourceencountered.Phase III activities includedcontinuedandmoreextensivetestingofthe geothermal resource,the drilling of a fourth temperature gradient hole,and an electrical resistivity survey to delineate the extent of thereservoir. Under Phase I,the first three temperature gradient holes were drilled in 1982 to depths of 1500 feet and encountered temperatures of up to 383°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 conclud- 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 of 1963)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 and others,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 temperaturegradienthole,and conducting an electricalresistivitysurvey.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.Theelectricalresistivitysurveyrevealedthatthe site of the current exploration well is ac- tually the most accessible site for encounter-ing the geothermal resource at a reasonabledepth(Republic Geothermal,Inc.,1984b). Flow tests and reservoir analyses conduct- ed in 1984 confirmed a highly productive geothermal reservoir (Economides and others,1985).Sustained flow of 63,000 ib/hr wasachievedthroughthethree-inch diameter wellbore with Jess than two psi pressure drawdown from the initial 494 psi bottomhole pressure after 34 days.The productivity indexderivedfromtheflowtestwasinexcessof 30,000 1b/hr/psi,which indicates a phenomenalpermeability-thickness product in the range of500,000 to 1 million md-ft.Wellbore flowmodelingindicatedthatacommercial-size wellatthesiteshouldbecapableofflowratesof 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 dailyscheduledairfreightandpassengerflightsand regularly scheduled barge service fromAnchorageandSeattle,its distance frompopulationcentersmayincreaseconstructionandoperationexpensesbyafactorof50%or more over continental U.S.costs. The Makushin geothermal exploration wellsite is located approximately 13 miles westoftheCityofUnalaskainaremote,rugged,roadless 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 milesofsteep,rocky slopes and canyons.Thislocationwouldclearlyhavea_significant effect on the costs of both construction and operation of a power plant at the site and atransmissionlinetotheCityofUnalaska. 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 otherregionsofthestate,heavy construction isgenerallylimitedtoafour-month construction"window"due to wind and snow conditions.Even during summer months,when the average tempera- DEVELOPMENT POTENTIAL OF THE MAKUSHIN GEOTHERMAL RESERVOIR OF UNALASKA ISLAND,ALASKA David Denig-Chakroff?)John W.Reeder 2)Michael Jd.Economides (2) (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 have confirmed the existence of a_productive geothermal reservoir beneath Makushin Volcano on Unalaska Island in the Aleutian Chain.A prelim- inary economic analysis has been conducted to determine the potential for developing the 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 atMakushinVotcanonearUnalaskaandisinvolvedin studies of both energy needs at Unalaska and alternatives for meeting those needs,including the geothermal alternative.The Alaska PowerAuthorityisastateagencygovernedunderexecu- tive and legislative oversight by a seven-member board of directors appointed by the Governor ofAlaska.Its goal is the orderly and economic development of energy resources to provide power at the lowest possible cost to the consumer and to encourage the Tong-term economic growth of the state. One objective of this paper is to summar- ize 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. oe ee AL ORF TOD Po PS MK pase ca . @ THemsar caacrent HOLES >GRO THERMAL RESOURCE WELL 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 atMakushinVolcanolocated14mileswestofthe PREMIER GEOPHYSICS INC. E-SCAN®Resistivity Services 307-100 West Pender Street Vancouver,British Columbia Canada V6B IR8 Telephone (604)684-2212 FECEIVFOPRY OO, Mr.David Denig-Chakroff ALAS?Os Alaska Power Authority 334 W.Sth Avenue c May 13 MO 54Anchorage,AK 995@1 May 1,1986 Dear Mr.Denig-Chakroff: re:Paper on Unalaska to be presented to GRC meeting,1986. Enclosed is a copy of the summary of a paper proposed for presentation at the Geothermal Resources Council annual meeting at Palm Springs in September.I have secured the verbal permission of Brent Petrie for the presentation and publication of general commentary on our role at Unalaska, subject to approval of the material by the APA.Brent indicated that such material should be sent to you for review. The paper has been submitted to the GRC;it can be withdrawn if there is difficulty on the APA's part with the content. Thank you. Yours truly, ¢ PREMIER GEOPHYSICS INC. breg A.Shore.E-SCAN®Resistivity Services 307-100 West Pender Street Vancouver,British Columbia Canada V6B IR8 Telephone (604)684-2212 Greg Shore,President MINING *GEOTHERMAL *GROUNDWATER PETROLEUM °EOR °CIVIL *NUCLEAR WASTE MINING *GEOTHERMAL *®GROUNDWATER ®PETROLEUM ®EOR ®CIVIL ©NUCLEAR WASTE Mapping the Makushin reservoir with 3-D E-SCAN resistivity Greg A.Shore and Andrew J.D.Ryder Premier Geophysics Inc.,Vancouver,British Columbia Canada Abstract In 1983,a high-temperature geothermal reservoir was identified at well ST-1 in an area of extreme terrain on the southeast flank of Makushin Volcano. The lateral extent of the reservoir had not been defined,and it was thought that it might extend to the northeast,into an area of road access and more economically viable development costs.The severe terrain had ruled out the use of conventional resistivity methods for reservoir mapping,and the delineation of the reservoir appeared to require the continuation of the successful (but expensive) program of temperature gradient drilling.On learning of E-SCAN's rough terrain resistivity capability,the Alaska Power Authority requested a 3-D E-SCAN of the Unalaska Geothermal Project area in 1984.The 3-D E-SCAN survey results unambiguously defined the boundaries of the reservoir,confining it to the area of extreme terrain in the vicinity of producing well ST-1, The northeastern boundary of the resource is marked by an inclined fault that appears to control the production intersected in well ST-1.Extension of the reservoir into adjacent areas of easier and more economic access was ruled out by the E-SCAN resistivity results, By the end of 1983,the Makushin Volcano geothermal project of the Alaska Power Authority on Unalaska Island had progressed to an advanced but still unresolved pre-development stage.Flow-testing of well ST-1 confirmed the presence of a geothermal resource in the upper Makushin River valley,but the various types of exploration data (geologic mapping,temperature gradient drilling, geochemistry,SP)accumulated to that date could not provide a definition of the geometry and in particular the lateral extent of the resource. The successful well ST-1 was located in rough terrain along an alignment of surface thermal manifestations extending around part of the southern flank of Makushin Volcano (Figure 1).The cost to develop the resource at that site would be considerably higher than the cost of development in an area of road-accessible terrain some 2 km northeast,down the valley from ST-l.Little was known about this area,except that it was in line with the trend of thermal manifestations leading to ST-1,and that a steam vent provided evidence of elevated temperatures in the area.Much of the geology of potential exploration interest lay hidden beneath a fresh,glassy flow which blanketed the area.prior to consideration of the feasibility of development at the site of well ST-1,it was appropriate to test the more economically accessible areas down the valley,for either a northeast extension of the high- temperature system identified at well ST-1,or -perhaps a separate resource occurrence. Resistivity methods had not been used on the island,because of prohibitively rough terrain. Producing well ST-1 had been discovered principally on the basis of geological mapping and temperature gradient drilling.When in 1983 the rough terrain capability of the E-SCAN resistivity method was presented to the GRC annual meeting at Portland, representatives of project managers Republic - Geothermal Inc.and of the Alaska Department of Geological and Geophysical Surveys decided to try the method at Makushin, The E-SCAN resistivity survey objectives were established as twofold: -map the characteristics and extent of the high-temperature resource identified at well ST-1,and, -test the economically more accessible area down the valley for resource potential,either an extension of the ST-1 resource or a separate system. A third area was appended to this survey coverage, extending further northeast down the valley,to test an area of outcropping crystalline rocks similar to those intimately associated with the surface thermal manifestations near well ST-1. While there was no evidence of thermal activity in the surface geology of this area,an assessment of deeper conditions with resistivity was considered prudent,given the potentially favorable geologic setting and direct road access, In the summer of 1984,a 3-D E-SCAN resistivity survey was operated over the 26 square kilometer Map area to test the objectives described above. The planning of the survey was straightforward: within an outline of the total area of interest,an electrode grid at 300 meters spacing was established,using air photos and maps for Shore and Ryder location.No other survey parameters were required.The survey swept from one end of the area to the other in four weeks,obtaining over 10,000 individual resistivity measurements of every orientation and at depths to 2000 meters.The survey results were continuously updated on an eight-color plotter,allowing the survey operator (and project geologist)to observe as the data outlined the extent and boundaries of the reservoir and tested the road-accessible areas along the valley. The survey results clearly and unambiguously answered all of the unresolved exploration questions (Figure 2}.«he boundary of the reservoir beneath well ST-1 was found to lie just 200 meters northeast of well ST-1,sharply cutting off the possibility that the reservoir would extend down-valley to the lower-cost road-access area.As the survey coverage proceeded,the road-accessible area was intensively tested for the presence of a separate resource zone;no resistivity signatures typical of those marking the ST-1 reservoir were mapped.The more resistive,non-resource resistivity signatures persisted through the remaining area of survey coverage.Verification of a lack of deep thermal activity in the area of crystalline rock completed the E-SCAN assessment of the project area. The exploitable reservoir was thus defined as being fault-bounded and limited in down-valley extent to just a few hundred meters beyond the producing ST-1 well,The remaining portions of the 26 square kilometer test area,including all of the low-cost road accessible area,were unequivocally shown to be devoid of the resistivity conditions.typifying. the reservoir at well sST-1. The master data set was divided into four plan plots of multidirectional data at four horizontal levels,200-500,500-1000,1000-1500, and 1500-2000 meters depth (Figure 3,4).These plots identified the gross three-dimensional distribution of resistivities,outlining theboundaryofthereservoirarea,and clearly distinguishing the reservoir from an adjacent 1 km thick conductive non-reservoir rock unit overlying a resistive basement.A third conductive feature near a steam vent in the high-interest road-accessible area was also identified as a shallow (500 meters)skim of conductive material over a uniformly more resistive lower unit,and thus of no potential resource significance. The master data set was also sliced vertically into four sets of parallel pseudosections through the survey area,separate sets of sections facing west, northwest,north,and northeast (Figure 5).These pseudosections provided additional correlation of the initial three-dimensional observations obtained from the plan plots,confirming the initial assessment of reservoir boundaries and the explanations of the other shallow conductive zones. The equivalent of over 320 line kilometers of resistivity pseudosections extending to depths over 2000 meters were constructed from the data set. Using the great density of measurements to advantage,subsets of data were organized and digitally stacked to provide emphasis of subtle resistivity features indistinguishable in individual pseudosections.A number of structural features (faults,contacts)were thus mapped at various orientations throughout the area.The largest of these features bisects the area,and marks a sharp transition from general lower resistivity of all rock types on one side,to a universally higher resistivity mode (10 times higher)for the same suite of rocks on the other side.This large scale,buried structure had not been previously mapped and was not identifiable. from ground or airphoto observations. Computer-assisted 2 1/2 dimensional forward modeling of selected pseudosections yielded a unique 3-dimensional model of the reservoir geometry and boundary locations (Figure 7).The identification of a dipping fault plane underlying the reservoir corresponds with the depth of intersection of open fractures from which steam is produced in well ST 1.The fault dips westward beneath the area of hot springs and fumaroles lying in inaccessible terrain southwest of the survey area.The presence of this fault and its associated permeability (encountered in well ST-1) indicates that a backup production well may be obtained by deepening the adjacent (presently non-producing)well E-1 to intersect the fault 300 to 500 meters below E-l's present drilled depth. The possibility of an extension of the resource into the economically favorable road-access area was eliminated by the E-SCAN results,while a simultaneous temperature gradient hole (TGH A-1)in the same area provided potential encouragement in texms.of.favorable temperatures (185.degrees C), The temperature in A-1 is close to that recorded in producing well ST-1 and adjacent non-producing well E-l,and from a strictly temperature gradient and BHT point of view,would support further drilling in the area to test for permeabilities associated with a possible resource extension or separate resource.The intensive mapping of this area with 3-D E-SCAN demonstrated that deep conditions were not similar to those around producing well sT-1, and that permeabilities capable of supporting commercial steam production likely did not exist. No further drilling in the area has been undertaken. The E-SCAN resistivity survey provided the first firm mapping of the resource's boundaries,and unambiguously rejected all other proposed possible sites.This enabled project evaluation and feasibility studies to focus on the single, confirmed resource site. E-SCAN's major contribution to geothermal exploration is its ability to simultaneously cost-effectively map every resistivity possibility through a given area,regardless of terrain conditions,without requiring assumptions or pre survey guesses on the part of the explorationist.The Makushin Volcano case history is an illustration of the effective use of this new exploration approach in an integrated multi-method program of exploration,in this case at an advanced stage of exploration. Se UNALASKA »\GEOTHERMAL EXPLORATION 4 PROJECTFadioo UNALASKA ISLAND,ALASKA E-SCAN RESISTIVITY SURVEY MAKUSHIN VOLCANO AREA JULY,AUGUST,1984LbéiAers@owe FOX CANYON °+o.¢Teeterecgeeeen,GEOLOGY AFTER ALASKA DGGS REPORT OF INVESTIGATIONS 84-3 RIF TWOOD ABBREVIATED KEY .Gal ALLUVIUM,COLLUVIUM +.Gvct VOLCANIC COLLUVIUM WALLEY Qvp PYAOCLASTIC DEBRIS ™Ghvf HOMOGENEOUS VOL- Ghvp CANICS:FLOWS AND PYAROCLASTICS GTvc INHOMOGENEOUS VOLCANICS Tu _UNALASKA FORMATION, >75%PYAOCLASTIC, SOME OYKES,SILLS Tuh METAMORPHOSED Tu, NEAR Tg INTRUSIONS Tuf FLOW-DOMINATED UNALASKA FORMATION Tg GABSRONOARITE SURVEY ELECTROOE SITE OAILL HOLE SITEA KILOMETERS 0 0.5 a 3.5 ;L \_j :THOUSAND FEET :0 i 2 3 a)j /¢soe,|i \\jyaretoolLoo. +¢N*:.. *te .|\*MAKUSHIN®|*2S PREMIER GEOPHYSICS INC.erp 4PmLetev:ae VANCOUVER,CANADA 2 tw se Ne Figure l Prior to the E-SCAN resistivity survey,the geothermal The survey plan employed a strategy which was not practical before resource was known to exist at well site ST-1 (upper the development of E-SCAN array technology,which is... left part of the map).The geometry and extent of the resource "When in doubt,assume nothing and measure everything." Survey coverage would start with intensive mapping of the known resource area 'around ST-1,and sweep northeast along the de'ined area of interest into the Sugarloaf and lower road areas,measuring resistivities in every orientation,to depths of 2000 meters. was unknown.The possibility that the resource extended down the valley to the northeast was of interest,since the cost of access and roadbuilding would be decreased substantially if the resource could be exploited from an area accessible from an existing road. Ae BB easwe2.ita @o-1 o o oo.; FOX CANYON A >e%- :.cyme . ge To":*MAKUSHIN®«+1,'eos -ndaVALLEY,+* .o*+feu ioe « 'UNALASKA \GEOTHERMAL EXPLORATIONfoPROJECT UNALASKA ISLAND,ALASKA E-SCAN AESISTIVITY SURVEY MAKUSHIN VOLCANO AREA JULY,AUGUST,1984 SUMMARY QF DATA INTERPRETATION ON COMPLETION OF FIELO SUAVEY. forior to any computer modeling) RESISTIVITY CONTACT OAR FAULT .SUAVEY ELECTRODE SITE @ ODARILL HOLE SITE KILOMETERSQo54 uu.THOUSANO FEET 1 2 3 L |,|1 i aeTT|PREMIER GEOPHYSICS INC. VANCOUVER,CANADA Figure 2 Interpreted results of the 3-D E-SCAN survey,Based on the resistivity data,there is no evidence prior to computer modeling of some aspects.of a continuation of the known system or of a separate The reservoir is sharply bounded by faults on the north resource within the 20 square kilometers of survey and east,within a few hundred meters of producing well area northeast of ST-1. ST=-l. *Roce,PAd wad Nar died ,fPAASY) HON \"=iP esasl-# oo"4 ARIF TWOOD wweee *.9 wz Be A Se oR DON ERS re OTNRea2LEaaWA}te ieee NY eS1aYONG:Sze}PLOTTED i fee gp we Boh ee ME cerSSTCMTEM200METERB"iy Uo RPE ON ea al PSPASSAataGreeWshelANSERLspelleeeeeom”,eka g 'yy me!tog |ope ''ae A .ne re 'wy \Mer wae t a o4e.t4 o ,.6 (he AM fee ','or TA a y \aka ava a -wf E wat ta.AA POAFP,BLOF TED!fos2e OF TOTAL SET.OF.10570,OMTA.!fC ut BASOSTAIN eee ce ©'ae x5 ay |ne .!oa \.All )oid |'whey)”:s\AN ah "j id AT ee ne 0 Nta ae |yg cb VoiePALElpeteLANMAONNASarPEELPeony Reproduced from 4-colour original APPARENT RESISTIVITY OHM-METERS UNALASKA =<30 Figure 3.This is a summary plot GEOTHERMAL EXPLORATION -=;7 j of all 10,322 apparent PROJECT -78resistivitymeasurementscomprising a80 the master data set for the area.UNALASKA ISLAND,ALASKA -158 Each datum is plotted nominally at E-SCAN RESISTIVITY SURVEY =noo the mid-point between the two MAKUSHIN VOLCANO AREA =ooelectrodesites(+)from which the .>700 measurement originates.The length JULY,AUGUST,1984 >708ofthelinesegmentindicatesthe-1800 apparent resistivity value as per the scale at right.In working plots,resistivity value is also indicated by color coding. PLAN PLOT OF POLE-POLE ARRAY APPARENT RESISTIVITY IN OHM- METERS.AANGE OF EFFECTIVE PENETRATION (Ze)IS APPROX: The orientation of each line segment 200 TO 2000 METERS °oh TLOME TERS 1s indicates the orientation of the 'I |-| measurement.The plot shows that most of the survey area is THOUSANO FEET repeatedly sampled with measurements oriented in different °'@ >4 _§Girections.Thus,while achieving a dense sampling across the survey area,a comprehensive testing of resistivity isotropy characteristics is also obtained.Anisotropic conditions may indicate linear features such as fissures,fracture sets,faults, or boundary conditions. +SURVEY ELECTRODE SITE e DAILL HOLE SITE PREMIER GEOPHYSICS INC.VANCOUVER,CANADA Shore and Ryder ft r DEPTH:200-500 METERS Figure 4 A sequence ofprogressively Some IN OS 4 deeper horizontal "slices" ,' through the master data set reveals the gross three- dimensional resistivity characteristics of the Ps Shale aS ST ee project area.The workingeoPALSTDeecy”field plots use color coded resistivity values, providing simpler visual grouping of values. :"FOX » Left,-At shallow depths of »investigation,the data show ""two areas of anomalous low resistivity.The fresh, classy flow (Fox Canyon past .Sugarloaf)is highly a er ft t 4a?yesistive. ape DEPTH:500-1000 METERS LSS, Deeper,anomaly 1 shows two subzones,A and B.In subzone B more resistive values are becoming apparent. Anomaly 2 is no longer seen. Resistive rocks beneath the shallow conductive zone now prevail. 'a ar] 1000-1500 METERS Deeper Still,Anomaly 1A SO continues to show low resistivity values. Anomaly 1B shows only the resistive rock unit underly- ing the shallower conductive layer. Anomaly 2 area reports continuing high resistivities at depth. Bf "A JV,ok ry Were ST OS S/e "¥ ,.aoe __At 1500-2000 meters depth,oF anomaly 1A remains stronglyTERSconductive.Nominal mid-array plotting positions for data accounts for the anomaly's apparent displacement. ae Pept ...4 ;ceo Ob of Wa /-,>eaea?of ME Ot)CANYON."2 tn A a APPARENT RESISTIVITY OHM-METEAS , am :-Sy8BINNSanewy 7,Veet er Seen yee aa sores fog«RESISTIVITY DATA:Aea"PSEUDOSECTIONSio"4 PACING WEST.'tf > wre iye4 ofA ¢RESISTIVITY DAUA ae ey Cr a\lt le ct'PSEUDOSECTIONS rica.GAY N,y\ey nLve2RACINGNoamaosa"NA eyryhhee;"maaaneeDo:yy Figure 5 The master data set contains the indiv- idual measurements for a wide range of plan and section plots.Above are plan plots showing the locations of four sets of resistivity pseudosections extracted from the master data set. The pseudosections are plotted in sequence,exactly as they would be if a conventional survey system had operated survey traverses along the routes shown above.The reader is reminded that virtually all of the "traverse"locations shown above could net "Pgebosect2Ons.Axso.NYae not be physically traversed by a survey crew.The E-SCAN pseudosections of data are available because once the electrodes were installed,all of the "traversing”was accomplished by electronic signals over the scanning network.As a result,features of interest anywhere on the property can be examined in detail,calling on plan and pseudosection data plots which slice through the area of interest from every orientation and depth.Interpretations suggested by data from one pseudosection are checked against data plots of other orientations. E-SCAN RESISTIVITY SURVEY,MAKJSHIN VOLCANO AFEA July,August,1984 POLE-POLE ARRAY pseudosections,looking vESTApparentFesistivityinona-retercs. Vertical scale is array effective venetration (22);see text. Peeudosecton ¢§1 g-4 ST-3 avi Sl ><51° 7 42 61 169 «69 137,4a 5042912012628)4d e188 4 i i i L L 1 lL 1 1 1 1 i 409 101 104 839110Pamo84 94 2677 a-500 a3 n2 1 119 123/19 22197199 136a __48 152 1sefo)122 63 199 164 170)185-1000 83 6 «21660/200 «173182ynrt)180 216 2x9165 20766221-1500 163 199229289 146 115 25 22 26 229 245 =2000 2e,METERS Figure 6 This is one of the pseudosections shown in the location plots of left,the deep,low resistivities of Anomaly 1A are identified in section. Figure 5.It passes through three wells,E-l At right,the data show the shallow and ST-1 within the identified reservoir area,conductive zone measurements of the'and A-1 southwest of Sugarloaf.Some of the area west of Sugarloaf (Anomaly 2), characteristics illustrated in Figure 4 plots which yield to more resistive values can be seen in the pseudosection above.At in the underlying rock (as in Figure 4). T ¥T T r T T T ¥Y *'Mi ' °°fe]fe]3°fe]fe]fo]° °fo]°o to]fe]fo]°tJESz3g33gS SECTION 10% SECTIONS CnosE:\>*\>4 j?4 \* 1000 ant"4 sta Lf °o ¢fw e ewits23:8 -§2 82 ¢3 8eA""Hy \L 1 i'4 a.7 =*F nominal topo50011000|50 J (not digitized)1 )20 7 #00 MEANSEa 9 : 300 100 Lever |<50 500 -1000J500: Figure 7 This is one of many two-dimensional sections through a common three-dimensional model which -describes a wedge-shaped reservoir connected to extensive low resistivity conditions (reservoir)off the section to the left. Well ST-1 achieves production from open fractures near thebottomofthewell;the rock above is tight and impermeable.The sloping fault mapped by 3-D resistivity as the lower boundaryofthereservoirmaybetheconduitsupplyinghotfluidsfromtheextendedlowresistivityzoneoffthesectiontotheleft. 'If this is the case,then additional production might beachievedbydeepeningwellE-1 to intersect the fault plane. JULY, UNALASKA GEOTHERMAL EXPLORATION PROJECT UNALASKA ISLANO,ALASKA AUGUST,1964 E-SCAN RESISTIVITY SUAVEY -2000- MAKUSHIN VOLCANO AREA INTERPRETEO TAUE RESISTIVITY SECTION ; SECTION @ 104 RESISTIVITIES:OHN-METERS -3000 |PLOT SCALE UNITS:METERS