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HomeMy WebLinkAboutAleutian ARC hot springs Unalaska section 198110-J21LH Geo \Yroyea WAG STATE WE ALASKA /2meZnce DEPARTMENT OF NATURAL RESOURCES P.O.BOX 80007 COLLEGE,ALASKA 99708 DIVISION OF GEOLOGICAL &GEOPHYSICAL SURVEYS PHONE: (907 479-7122 October 9,1981 Ms.Patti DeYoung Alaska Power Authority P.O.Box 843 Anchorage,Alaska 99501 Dear Patti: You will find enclosed a draft copy of the Aleutian ARC hot springs open-file report and of the Unalaska section excerpted from this report.Please note that the report is still preliminary and has not been reviewed by the State Geologist.Our publications section is catching up with its backlog and the finished product should be published within a month. The information contained in the Unalaska section,along with John Reeder's report,should be beneficial to your program.We are presently working up data on two additional thermal areas that we found on Unalaska this past summer.I am certain this information will also be of interest and I will send you a preliminary draft describing these areas when it is completed. As it will become apparent from reading my report I am particulary interested in understanding the deep hydrothermal systems associated with volcanoes and their probable connection to shallow magma chambers.The evidence strongly suggest that such a system exists at Makushin volcano.I would therefore greatly appreciate your keeping me informed on the progress of the drilling program at Unalaska. Please feel free to call me should any questions arise regarding the contents of the open-file report or the geochemistry of thermal fluids at Unalaska. Good luck. Cheers, Kemiast ,Motilea (Sage)'Roman J.Motyka cc:John Reeder 24-07 -ol t wag Of f Aso ,Sg ae *re , rt)whe °gk y oyet coo 4 yo woe ast ae we A ea ath PY sureties BY"gale ,cai?cab 2,ypecIEvieLy0aie8oyGeeoatgoreevosthvanseeYehCoecoveCHSookcowsSh15"4ooidcor=kcoorotger8 UNALASKA GEOTHERMAL AREAS EXCERPTED FROM Alaska Open-file Report ASSESSMENT OF THERMAL SPRINGS SITES ALEUTIAN ARC,ATKA ISLAND TO -BECHEROF LAKE --PRELIMINARY RESULTS AND EVALUATION By . R.J.Motyka,M.A.Moorman,S.A.Liss UNALASKA ISLAND Background Unalaska Island,second largest in the arcuate chain of Aleutian Islands,is located between latitudes 53915'and 54°N.and between longitudes 166°and 168°W.,200 km southwest of the Alaska Peninsula (fig.1).The island is about 140 km long and 60 km wide and follows the trend of this segment of the Aleutian arc,which is about N.60°E. (Drewes and others,1961).Most of the island is ruggedly mountainous and,except for the northern bulge,the coastline is deeply indented by fjords (fig.By.Beaver Inlet,which is more than 30 km long,and Makushin Bay,about 16 km long,split the eastern and western ends of the island,respectively,and separate northern Unalaska from the elon- gate southern portion. The western part of northern Unalaska (the northern bulge)is dominated by the still active Makushin Volcano,which is about 2035 m 4high.The broad dome-shaped summit has a small calder,and is capped by a glacier with tongues that descend the larger valleys to elevations as low as 300 m (1000 ft).Several symmetrical cones and craters occur on the flanks of the volcano. The terrain immediately around the volcano and extending eastward Spm " of it is characteristically rugged with deep glacier-carved valleys, sharp ridges,and peaks.Two broad glacier valleys,Makushin Valley and Glacier Valley,originate on the flanks of Makushin volcano and extend to Unalaska Bay and Makushin Bay,respectively.Unalaska Bay,a deep embayment into the northern coast of the island with several sub- sidiary inlets,lies about 20 km east of Makushin Volcano, Much of the island is discontinuously veneered by a thin mantle of till, volcanic ash,humus,and soil.The only trees on the island are several groves of Sitka spruce,planted by Russians in the 19th century around Unalaska Bay. Willow thickets grow at low elevations in the more protected valleys;blueberry shrubs and salmonberry and crowberry plants are common.The lower elevations and valley bottoms are characterized by tundra vegetation.During the summer the meadows are abloom with a large variety of flowers. Unalaska village,theheedquarters_for-the Unalaska_Native-Coer poration,. lies on the southern shore of Iliuliuk Bay near the head of Unalaska Bay.The only other permanently inhabited place on the island is a sheep ranch at Chernofski Harbor.The Unalaska community has a permanent resident population of about 600 people,most of whom are Native. Unalaska village was first visited by Russian fur traders late in the 18th century.During the 19th century,the village became a Russian outpost and a major center for the Aleutian fur trade and Russian Orthodox Church.The purchase of Alaska by the United States in 1867 and the rapid decline of fur-bearing sea-mammal populations later in the century led to a gradual decrease in White population and influence in Unalaska until 1942. During World War-II Dutch Harbor,located on Amaknak Island adjacent to Unalaska village and now connected to it by a bridge,served as a major U.S. naval base and staging area for Allied operations.The surrounding hillsides are still littered with rusting Quonset huts,old tunnels,artillery emplacements,pillboxes,and look-out posts.The Dutch Harbor area itself " contains row upon row of deserted barracks and warehouses,some of which areLovmolLebaenowbeingreclaimedandrenovatedbythe,Native corporation. Because of the large and excellent deep-water harbor located in Unalaska Bay (one of the few protected harbors in the Aleutians),the village has naturally evolved into the major base of operations for the Bering Sea fishing industry.Tnirteen fish processors operate in the area and bring in as many as 1,500-2,000 seasonal employees during the height of crab-fishing season., Unalaska has the distinction of being the crab capital of the world.With the Im fm mtn.elopment of the Alaskan bottom fishery,Unalaska will undoubtedly continue to expand.The village council is actively seeking an energy base to support its growing fishing industries. | Geology The geology of Unalaska Island has been described in Drewes and others (1961).The Unalaska Formation constitutes the oldest and most extensive group of rocks in the island and consists of a thick sequence of coarse and fine sedimentary and pyroclastic rocks intercalated with dacitic,a cae andbasalticflowsandsills,cut by numerous dikes and small plutons)ie formation is exposed over two-thirds of the island and is thought to be early to mid Miocene.The formation has been extensively folded,faulted,and intruded by plutonic rocks,with moderate hydrothermal alteration occurring 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 crystallization of a granodiorite magma that invaded the rocks of the Unalaska Formation by assimilation,stoping,and forceful intrusion (Drewes and others, 1961).The age of the pluton is considered to be younger than early Miocene and older than middle Pleistocene. Basalt and andesite flows and pyroclastic rocks of the Makushin volcanics unconformably overlie the Unalaska Formation and the plutonic rocks that intrude it (Drewes and others,1961).The Makushin Volcanics constitute most of Makushin Volcano,a broad volcanic dome more than 1,800 m high and 16 kn wide.The thickness of the Makushin Volcanics varies greatly but probably does not exceed 1,500 m-Most of the Makushin Volcanics are believed to be middle to late Pleistocene.Much of the basalt and andesite is extensively glaciated and must precede at least part of late Pleistocene time. Late Wisconsin to Recent volcanic cinder cones,composite cones,and lava flows are scattered about the base of Makushin Volcano amd have been collectively mapped as Eider Point Basalt (Drewes and others,1961).These volcanic rocks rest unconfomably on glaciated rocks of the Makushin Volcanics and in places on 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 magma into the fissure at shallow depths. Makushin Volcano is still active and is known to have erupted at least 14 times since 1760,with a report of a minor eruption occurring in 1980 (Coats, 1950;Sean,1980);Table Top Mountain has probably been active since the last major glaciation (Drewes and others,1961). The island has been intensely glaciated and glacial landforms are prominent everywhere.The mountains contain U-shaped valleys,cirques,aretes, and ice-scoured features of every size.An ice field of 40 km2 caps Makushin Volcano with glaciers descending as low as 210 m (700 ft).Till from the latest Wisconsin ice advance occurs in the lower cirques and valleys.More recent,fresh-looking moraines,located near existing glaciers,indicate small advances and recessions have taken place,perhaps within the past few hundred years (Drewes and others,1961). Faults,joints,and related linear features are abundant,but the length, direction,and amount of displacement have been determined for only a few of theme Most of the faults are nearly vertical.The strong topographic alignment of Beaver Inlet and Makushin Bay,which nearly bisect the island, suggests a major fault.A statistical analysis of linear topographic features from aerial photographs performed by Drewes and others (1961)showed a dominantly northwest trend in the Unalasl.a 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. Thermal Areas Several active thermal areas have been identified on northern tnalaskaIsland,and all but one are associated with Makushin Volcano cigs oy Fumaroles and hot springs occur within the 2.5-km-dia Makushin caldera and were first investigated by Maddren (1919),who reported the existence of an extensive solfatara field ( * 30 acres)near the center of the caldera. Fumaroles were audible at distances of over 2 km,and the temperature at the orifice of one of the smaller fumaroles measured 150°C.The continued existence of these high-pressure fumaroles emitting large amounts of vapor was verified during the summer of 1980 (J.Reeder,pers.commun.). An extensive fumarole field and associated hot springs mentioned in Drewes and others (1961)occur at the head of Glacier Valley in the south-southeastflankofMakushinVolcano(fig.24).The fumaroles lie at an elevation of about 670 m.A smaller fumarole field,found in 1980,occurs near the toe of a glacier located about 1 km northwest and about 150 m above the previous site. Another fumarole field containing a large,highly pressurized fumarole occurs further west on the south flank of the volcano at an elevation of about 900 m (J.Reeder,pers.commun.). Two fumarole fields and associated hot springs were found in the Wpper2reachesofMakushinValleyonthenortheastflankofMakushinvol.The lower and smaller field occurs at an elevation of about 360 m on a small bench located on the steep north valley wall about 25 m above a stream channel ¢ffg@. UW The larger field occurs about 2 km further upstream at the head of one of the tributary valleys on the east flank of the volcano at elevations varying from 600-800 m. One additional hot-spring site occurs on the island and is located about nein.4iy 200-m.south of Sunmer Bays This spring is probably the same as that reported by Dall (1870)near Captain's Harbor. 'The hot springs near Summer Bay are located within the Unalaska Formation. The hot springs and fumarole fields at the heads of Makushin and Glacier Valleys also occur in that formation and in the plutonic rocks that intrude it. The other fumaroles and hot springs occur in the younger Makushin Volcanics. During July 1980 the DGGS field party was able to examine briefly the thermal areas at the heads of Makushin and Glacier Valleys and the hot springs site near Summer Bay. GLACIER VALLEY THERMAL AREA Location ; Latitude 53°50.8'N.,longitude 166°53.0'W.; Unalaska 1:250,000 Quadrangle,1951. General Description The thermal area is located at the head of Glacier Valley,a 3-to eal4-km-wide U-shaped valley that trends north from Makushin Bay for Lobe,"The head of the valley terminates in a series of steep ravines in the south-southeast flank of Makushin Volcano.The active summit caldera of the volcano lies about5 km northwest of the thermal site;Pakushin cone,a recent parasitic pyroclastic cone,is located about 6 km southwest of the site.The rugged ridges neighboring the thermal area are 600-900 m high and intensively glaciated. The thermal sites are located on and above the easternmost branch of the Glacier Valley river at the very head of the vali There are three areas of thermal activity.The first two,a fumarole field and a series of hot springs, occur on a ridge lying between two ravines in which flow the streams that comprise the headwaters of the eastern branch of the main valley river.About 0.5 km downstream from the juncture of these two streams,another series of hot springs and seeps occur at the base of the eastern valley wall near the stream bank.In addition to these sites,a small area of fumaroles and boiling waters was found emanating from a pile of volcanic boulders on the western margin of a glacier in the adjoining western tributary valley,about 1 km northwest of the principal site.Still farther west,a highly pressurized fumarole occurs at an elevation of about 900 m. The thermal area in Glacier Valley is remote and relatively inaccessible. The DGGS field party reached the sites by helicopter from the village of ok=oSUnlaska,which lies about (32 km east Jof the thermal area.The sites can alsoeeeeeeNNbereachedbytakingaboatintoMakushinBayandthenwalking”10 i up Glacier (48 Valley.Ys )ee Geology The fumaroles,steam vents,and hot-spring waters emanate from an area of intensely hydrothermally altered rocks belonging to the Unalaska Formation and the gabbroic plutons that intrude it.The hydrothermal alteration,consistingCroreteeoeemittmainlyofkaortntte,is the result of interaction of near-surface rocks with acid waters that are formed by the condensation of hydrogen-sulfide-rich steam in meteorically derived,shallow ground waters.Fumarolic activity extends up a ridge to an elevation of about 640 m,where it is capped by a 30-m sequence of shallow dipping,interbedded basaltic flows that originated from Makushin Volcano.The exposure of the flows above the fumaroles is nearly vertical, apparently due to plucking by glacial erosion.These flows do not appear to be altered,i or does the surface expression of the fumarolic activity extend beyond the flow-contact boundary. Although much of the area surrounding the thermal site has been intensely glaciated,the Makushin Volcanics exposed at the higher elevation above the thermal zone appear to have had substantially less erosion and may have been emplaced at the close of or after the Wisconsin glaciation.Several fresh moraines occur adjacent and below the zone of thermal activity at elevations of 300-600 m,and are evidence for recent glacier advances.A glacier still resides in the adjoining western valley and descends to an elevation of about 450 m.Lower portions of -the valley are floored with.glacial drift,alluviu, and colluviun. Numerous fossil fumarolic vents and hydrothermally altered ground were found in a small,recent glacial moraine located near the juncture of the streams below the hydrothermally heated ridge.One fossil vent occurs in a cone-shaped,4-m-dia,1.5-m-high mound cf hydrothermally altered clays.The fossil vents suggest the area was active at least during the waning stages of the last glaciation which,at this elevation,may have occurred as recently as a few hundred years ago. Drewes and others (1961)mapped a steep normal fault southeast of the thermal sites.The trend of the fault,N.50°W.,is directly in line with the thermal sites and Makushin caldera,and may be providing conduits for thermal fluids to ascend to the surface. Fumaroles and Hot-springs characteristics The site consists of three areas of thermal activity that are separate but probably related. a.The first zone consists of numerous small fumaroles and stream vents,all at boiling point,dispersed over an ara of about 10,000 m*and emanating from a series of small knolls and gullies cut into the hydrothermally S59 altered ground (£tg7>25.The vents occur between elevation of 4,800 and 680 fa 2;100 ff below a steep cliff of volcanic flows and between two forks of the(5)eastern tributary to the main valley river.Orifices are generally a few centimeters or less in diameter with sublimates commonly ringing the vents. Gases are mostly steam.The vents have characteristically low flow rates, although several are moderately pressurized and have vapor plumes several meters high. Waterfalls from the lava cliff face above the fumarole field channel a large flux of surface meteoric waters onto and through the fumarole field. Where the waters pass over fumaroles they are heated by condensing steam, in some cases to the boiling point.Much of the water appears to percolate into the ground after passage through the thermal zone. b.The second area of thermal activity consists of several hot springs and seeps located on a small bench indented into the bluffside at the base of (digs.a?tw ) the ridge containing the fumarole field,The springs occur at an elevation of about 380 m and cover an area of about 1,000 m2,perched several meters above the juncture of the two streams that drain the thermal area.A recent glacial moraine containing numerous fossil thermal vents occurs immediately southeast of the springs. Spring temperatures ranged from 76°to 96°C,and the combined flow from the thermal springs was visually estimated at 200 lpm.The thermal waters typically emerge into shallow pools averaging about 1 m in dia in what appears to be glacial drift.The upper portions of the hot-spring calertochannelswerecommonlyveneeredwitha1 to 2 cm-thick layer of sttiICeous| Sinter-tfor-co With-previeus-tsere Orange bacterial mats and blue-green algae commonly lined the channels farther down stream.Flow from the hot-spring channels combines with runoff from adjacent snow patches (present on 8/11/80)into a single channel,which then drains along the adjacent moraine and into the cold-water stream below the springs. A few hot-spring channels were dry,indicating discharge may seasonally fluctuate with the availability of ground water.A small area of steaming ground occurs upslope and adjacent to some of these dry spring basins. The third area of activity consists of a 50 m linear zone of seeps and a few hot springs located about 0.5 km downstream from the previous hot-springs site (fig.24).The thermal waters issue from colluvium at the base of the eastern valley wall,several meters above the main stream channel.Water temperatures range from 17°to 78°C,with the combined flow visually estimated at 60-lpm.The waters emerge principally through seeps.Three or four small springs also occur,including one from a small stim sinter cone and another with an estimated discharge of 30 lpm.The - ; Caleta (Wm i ha 1 at ith sthiceouc-sinter..h of th-Tre spring channelsgare coated wi zo :Much of eeeae. oe a ! ee ercmrereeonat eesurrounding ground'is terraced with siliceous sinter,indicating flow mayaeo” fluctuate or may have been much greater at one time.Outflow of the thermal waters from the area is diverted by a medial moraine for several meters before it joins the main stream channel. Table 16 gives data on thermal waters obtained from site B and a partial -Cre i . - : analysis of a_sample from the cold-stream waters that drain the thermal area immediately west of the site. -Key features of the thermal water chemistry are the extremely low levels of chloride present,the nearly neutral pH,the relatively low cation content, and the comparatively high level of magnesium and calcium.The waters are similar to those that have been classified as bicarbonate-sul fate waters by others (White,1957;Mahon-and Ellis,1964).Such waters typically occur on at the flanks (or in wells drilled thereon)of active volcanoes in island-arc settings (Oki and Horino,1970;Mahon and others,1980). The partial chemistry of the associated cold-stream waters show them to be surprisingly high in dissolved solids,especially silica and sulfate. Evidently,thermal waters from higher on the flank of the volcano are mixing with cold waters and draining into the stream.'The high sulfate content probably arises from the oxidation of HS gases associated with the fumarolic activity. Reservoir Properties The chemistry of the thermal waters and the occurrence of the fumarole field indicate the present of at least a shallow vapor-dominated zone underlying the area.The magnesium and calcium contents of the thermal waters emerging at the surface indicates the waters are probably surface meteoric waters infiltrating to relatively shallow depths and being heated by steam rising from a deeper reservoir.The source of steam may ultimately be derived s from a dee;,boiling,hot-water system overlying a cooling magma body.The high silica content in the spring waters suggests temperatures in the shallow perched reservoir may approach 150°C,if equilibration with quartz is assumed. The large volume of steam escaping from the area and the large area covered by hydrothermal alteration and thermal activity indicate a hot reservoir system exists and that it probably exceeds 150°C. No geophysical exploration or exploratory drilling has yet been done at the site.The thickness of the perched water reservoir,the underlying vapor-dominated zone,and depth to the hot water or steam reservoir all need to be determined. Comments The fault system mapped southeast of this thermal area may provide conduits for the thermal fluids that are ascending from deep within the geo- thermal system.The trend of this fault and those of a large proportion of linear features on northern Unalaska,including those associated with Makushin Volcano,are approximately N.50°W.(Drewes and others,1961).This orienta- tion is about the same as the direction of convergence of the North Anerican and Pacific tectonic plates.Major tensional features are considered to pro- pagate in this direction,the direction of maximum horizontal compressional stress (Nakumura and others,1977).Such deep-seated fractures can provide avenues for intrusion of volcanic dikes and feeder systems for surface thermal vents. The setting and chemistry of the Glacier Valley thermal area is similar in many respects to thermal activity observed at other active island arc volcanic systems (Oki and Horino,1970;Mahon and others,1980).Detailed investiga- tions of such volcanic systems in other areas indicate that the heat driving the secondary hydrothermal reservoirs and producing the surface springs and fumaroles is derived from primary reservoirs of a hot sodium chloride brine that overlie cooling magma bodies.Temperatures in such thermal brine reservoirs are known to exceed 300°C.If such a deep high-temperature brine reservoir exists at Makushin,it may ultimately prove the most productive geothermal reservoir in the system. The occurrence of a high-temperature geothermal reservoir in the vicinity of a population center seeking to expand its fishing industry makes the detailed investigation of the Makushin geothermal resource attractive.One potential deterrent to the development of this resource is the volcanic hazards associated with the still-active Makushin Volcano. Table 16.Chemical composition and physical properties of Makushin Glacier Valley site-B hot springs 1 and 2 (All chemical analyses in mg/1.)M*Bl Bo oreE .DGGS DGGS shedemen t Z Characteristics Spring 1 .-Spring 2™colieeenan Togenoe ae S10,94 125 125 Al nd nd -- Fe 0.10 <.01 _- Ca 11.7 32.1 -- Mg 4.0 10.6 - Na 52.0 87.2 77.5 K 4.8 5.7 4.5 Li <0.01 <0.01 -- HC03 37 288 - SO,129 95 418 cl 10 5 10 F 0.14 0.28 -- Br nd nd -- I nd ond _ B <0.5 <0.5 -- HS nd <0.5 - Sr 0.07 0.26 -- pH,field 6.40 6.50 - Dissolved solids 342.81 649.14 -- Hardness (mg/CaCO3)45.76 82.4 - Sp conductance (umno/em at 25°C)360 580 -- T (°C)96.8 82.4 .666 Flow rate (lpm)nd nd = Date sampled 8/11/80 8/11/80 _- nd -Not determined. MAKUSHIN VALLEY THERMAL AREAS Location Latitude 53°55'N.,longitude 166°50'W.; Unalaska 1:250,000 Quadrangle (1951) General Description The Makushin Valley thermal areas are located at the head of Makushin Valley on the east northeast flank of Makushin Volcano,about 5 km east of the summit caldera (fig.26).Makushin Valley trends westward for 13 km from Broad Bay before terminating on Makushin Volcano.The lower part of the valley is a 3-km-wide U-shaped glacier valley,whereas the upper reaches of the valley consist of several small canyons incised into the flanks of Makushin Volcano. The canyons are flanked by steep valley walls rising 300 to 600 m above strean level.Ridge tops are commonly rounded plateaus and range from 300 to 900m high. The region has been intensely glaciated.A glacier still resides on the upper flanks of the volcano above the thermal area,and in places descends to elevations of 700 m.The upper part of the volcano,however,still retains the shape of a shield volcano. There are three areas of thermal activity that occur along the upper middle branch of the Makushin River (fig.27).The highest of these consists of a broad field of mild fumarolic activity,located between 640 and 820 m in elevation on the east-northeast flank of the volcano.The second area consists of a cluster of hot springs at an elevation of 570 m,located at the base of the ridge containing the fumarole field.The third area occurs about 2.5 km farther downstream and consists of a few steam vents and mild fumaroles with associated thermal waters. The thermal areas are relatively inaccessible and were reached by helicopter from the village of Unalaska,which lies about 20 km east of the sites.Although remote,the sites could be reached by following an old military jeep trail starting either from broad bay and going up Makushin Valley or from an abandoned airstrip near Driftwood bay and ascending to a basalt plateau at an elevation of 300 m,located north of the thermal areas.From there the sites can be reached by a 5-km cross-country trek. Geology Bedrock in the vicinity of the thermal field consists of a complex mixture of the Unalaska Formation and the plutons and dikes that intrude it.Recent. lava flows and pyroclastic rocks,collectively termed the Eider Point Basalt, occur immediately north of the thermal area (Drewes and others,1961). Outcrops on the ridge above the thermal field are altered porphyritic gabbros containing subhedral to euhedral phenocrysts of plagioclase, labradorite to bytownitite in composition,up to 8 m long,contained in a fine-grained groundmass of feldspars,pyroxenes,and sulfides.The gabbroic rocks are cut by basaltic dikes of similar composition.The fumaroles themselves emanate mainly from highly chloritized rocks of the Unalaska Formation.The ground surrounding the fumaroles has been intensely hydrothermally altered to varicolored clays,predominately kaolinite. The slope above the fumarole field is capped by a 20-m-thick series of five or six basaltic flows that probably originated from the summit of Makushin Volcano.These flows terminate in a vertical cliff face,formed by glacial erosion.The lava flows do not appear altered;the fumarolic activity does not extend beyond the cliff face. Fresh glacial debris is scattered over much of the thermal field, indicating the area was probably covered with ice during neoglacial advances. The stream bed below the fumaroles lies in a steep ravine floored with boulder- sized angular volcanic rocks. Fumaroles and hot-springs characteristics The thermal activity occurs in three different areas;two of the sites are probably related and occur in a cirquelike feature at-the head of the middle fork of.the valley.. ae Mild fumarolic activity covers an area of ah.0.25 km2 and lies between elevations of 640 and 820 m on the steep northeast slope of the middle fork of the Makushin River valley.The thermal field occurs near the headwaters of the stream and consists of numerous fumaroles and steam vents dispersed over a series of rounded knolls and terraces that form the valley slopes.Three broad terraces of fumaroles,each about 20 m wide, lead in steps to the vertical cliff of colvanic flows above the thermal field. The vents are mildly to moderately pressurized,with vapor plumes of several meters rising from the more active vents.Boiling water can be heard just below the surface at severalof the orifices,which indicates surface runoff is being heated by condensing steam.Fumaroles were at or slightly below the boiling point;associated pools ranged from 80°to 95°C.The orifices were commonly surrounded by sublimates and multihued- alteration clays.Several of the vents occurred in small bowl-shaped depressions;others emanated from small mounds of debris probably carried to the surface by the upflow of steam and gases. b.This site consists of a semicircular cluster of hot springs perched a couple of meters above stream level at the base of the cirque containing * -fumarole field A.The springs are located at an elevation of .Ne 560 m in a small bowl indented into what appears to be glacial drift.The thermal waters issue primarily from four principal vents,spaced about 1 m apart, each having an estimated discharge of Ne 10 lpm;thermal water also arises from several additional seeps in the marshy basin of the bowl.Outflow from the springs and seeps merge into a single channel before entering the main cold stream.Spring temperatures ranged from 80°to 87.5°C.Reddish oxides-stained rocks occur near the themal waters;orange sinter deposits and blue-green algal mats line the spring channels. Another series of thermal springs measuring up to 80°C occur about 50 m farther downstream along the banks of the main cold-water channel and at the base of a waterfall on the steep northern valley slope.The valley narrows beyond this point to form a small canyon several kilometers long. Ce The third site occurs at an elevation of".360 m on a small 30-m-wide bench located about 75 m above stream level on the steep northern wall of the valley,about 2.5 km downstream from the previous sitese Thermal activity consists of a 2,500-m2 area of mild boiling -point fumarolic activity, mudpots,and hydrothermally altered ground,and a thermal spring and some seeps about 100 m west and 4 m below the fumaroles.The fumaroles and spring emanate from colluvium accumulated on the bench.The hot spring has a temperature of 67°C and a low rate of discharge,visually estimated at less than 10 lpn. Table 19 gives the chemical and physical properties of thermal spring- waters obtained from sites B and C.These waters are similar in most respects to those found at the Glacier Valley site,namely,very low chloride,high silica,high proportion of calcium and magnesium,and relatively high bicarbonate and sulfate.The Makushin Valley springs are slightly more acidic. As in the Glacier Valley case,the comparatively high Ca and Mg content of the waters relative to the other cations indicates the waters are derived from a low-temperature reservoir or perhaps result from the admixture of heated surface waters with deeper,hotter thermal waters.The sulfate and bicarbonate probably result from the oxidation of HS and CO»gases rising from deeper in the volcanic system. 'Table 17 gives the chemical composition of fumarolic gas samples obtained from sites A and C.The dominant gas in both fields is carbon dioxide.Gases emerging from the upper fumarole field (site A)contain proportionately higher percentages of hydrogen sulfide and hydrogen gas than those emerging fran the lower thermal field (site C),perhaps because fumarolic gases at site C have had more interaction with ground waters.4 The low-concentration of oxygen inionebothcasesisprobablyduetooxidationofHSandH>-}The nitrogen and argon are probably of atmospheric origin,and are probably dissolved in infiltrating surface waters (Mazor and Wasserberg,1965). _- Reservoir Properties The occurrence of the thermal springs at the base of fumarole fields in Makushin Valley suggests that at least part of the spring waters may originate as condensation of steam in surface waters,which then percolate into the porous colluvium and country rock to eventually emerge as springs.The high Silica content of the thermal waters,however,indicates that a large portion of the waters must have originated from a subsurface reservoir where temperatures exceed 150°C,assuming the silica is in equilibrium with quartz. Surface waters infiltrating this reservoir may become heated on descent, causing dissolution of cations in the wall rock,a process aided in part by the slight acidity of the waters.The levels of calcium,and particularly Magnesium,relative to sodium and potassium indicate the residence time of waters in the reservoir is too short for these constituents to equilibrate to the estimated reservoir temperature.Silica can equilibrate rather rapidly, within several days to a few weeks.This suggests the reservoir supplying the therma-spring waters lies at fairly shallow depths.The low chloride content and the slightly acid-sulfate chemistry of the thermal waters,together with their association with fumarolic activity,are evidence for a perched reservoir supplied by meteoric waters that are heated by steam and volcanic gases rising through a vapor-dominated zone from a much deeper reservoir. \ | Tae hydrogen suliiae and helium probably have magmatic origins,as does as least part of the carbon dioxide (Craig,1963;flunite,1968).An analysis of the ratio of 2He:4He in the fumarolic gases obtained in cooperation with R. Poreda at the Scripps Institute of Oceanography is given below: MV-A -s MV-C(FHe/4He)sae 4.9 6.6(Snel tae)AIR(-He/*He)AIR An enrichment in 3He in fumarolic gases has been correlated with magmatic activity on a worldwide basis,the sourceof 3he thought to be derived from primordial mantle material (Lupton and Craig,1975;Craig and others,1978;R.Poreda,pers.commun.).The values for the Makushin fumaroles are within the range of other volcanic island-arc geothermal systems. The hydrogen content of the gases is probably produced by high-temperature | reaction of water with ferous oxides and silicates contained in the deep . reservoir rocks (Seward,1974). Table 18 gives the results of applying the D'Amore and Panichi (1980)gas geothermometer to the Makushin fumarole samples.From the proportions of,gases present,B is chosen as O and the respective reservoir temperature estimates are 278°C and 168°C for sites A and C.These estimates must be used with caution.The accuracy of this geothermometer has not yet been generally accepted.Furthermore,the gases have probably undergone reaction with a shallow reservoir which may have affected their n2s and H2 contents. Despite the uncertainties in the gas geothermometers,the large flux of steam and the probable magmatic origin of some of the fumarolic gases indicate the existence of a high-temperature,deep geothermal reservoir. Comments The Makushin Valley hydrothermal system is similar in most respects to the Glacier Valley system.Both are characterized by extensive fields of mild fumarolic activity and thermal springs low in chloride and rich in sulfate and bicarbonate.The proximity of these fields to each other and to the active summit caldera indicate a common source of heat underlies the volcano. Comparison with similar volcanic systems elsewhere in the world suggests the origin of the hydrothermal system is a high-temperature sodium-chloride brine overlying a cooling body of magma.Gases and steam escaping from this deep reservoir give rise to reservoirs rich in secondary bicarbonate-sulfate at shallower levels and to the fumarolic fields on the flanks and summit of the volcano. The postulated deep brine reservoir should be the ultimate target of any exploratory energy development program.The Makushin Valley site lies near the village of Unalaska,the capital of the Bering Sea fishing industry.An old military road exists along the lower part of Makushin Valley,affording potential access to the site.However,caution must be exercised before proceeding with any development plans because Makushin Volcano is still active. Table 19.Chemical composition and physical properties of Makushin Valley hot springs sites B and C (all chemical analyses in mg/1) DGGS Bg DGGS CcCharacteristicsSpring-I-Spring-2 Si0,140 88 Al nd nd Fe 0.09 0.03 Ca 69.3 23.1 Me 12.2 8.0 Na 28 13.9 K 5.6 3.4 Li <0.01 <0.01 HC03 191 116 SO,155.3 21.4 Cl 5 5 F 0.12 0.11 Br nd nd I nd nd B <0.5 <0.5 HS nd nd Sr 0.28 0.10 pH,field 5.48 5.32 Dissolved solids 606.9 279.04 Hardness (mg/CaC03)218.87 90.74 Sp conductance (mno/am at 25°C)600 255 T (°C)87.4 67.0 Flow rate (lpm)ond nd Date sampled 8/13/80 8/13/80 nd -Not determined.oe Table 17.Chemical composition of fumarolic gases from Makushin Valley thermal field (analysis in volume percent) Content Site A Site C He 0.009 0.003 Ho 0.49 0.025 Ar 0.083 0.0072 05 <0.0001 <0.0001 No 7.93 0.56 CH,0.0018 0.0031 CO 89.14 99.05 H»S>2.38 0.30 aj.Weldon and R.Poreda,analysts,Scripps Institution of Oceanography,La Jolla,Calif.bm.Moorman,analyst,DGGS. \ Table 18.Gas geothermometry,(1)Makushin Valley fumaroles (temperatures in degrees Celsius). BL Site A Site C -7 380 231 0 278 168. =7 204 119 (1)Equations from D'Amore and Panichi (1980): T=24775 273.15 A+B+36.05 where A =2 log CHY -6 log fil,-3 log HoS05C05CO> (gases expressed in volume per cent) and B=-7 for CO9<75%and CHy>2H7,H4S>2H5B=0O COz>75% B=7 CO<75%a\ SUMMER BAY HOT SPRINGS Location» Latitude 53°53.1'N.,longitude 166°26.9'W. Unalaska Quadrangle 1:250,000 (1951)T.73 S.,R.117 W.,Seward Meridian General description The Summer Bay hot-springs site is located near the base of the east slope of a north-south trending glacial valley about 2 km south of Summer Bay and 5.5 km west of the village of Unalaska.The springs occur at the edge of a marsh located about 0.5 km southeast of a shallow 1.5-km-long lake that occupies the northern part of the valley.Glaciated ridges surrounding the valley rise up to 550 m in elevation. The site can be reached from the village of Unalaska via a jeep trail up the Unalaska River Valley,over a 460 m pass and then north into the unnamed valley containing the springs;the 12-km trip requires about 2 hr.There is also a road from Unalaska village to Summer Bay along the coast of Iliuliuk Bay,but it is disrepair and blocked by landslides and washout s in sever! places.Both roads date from WW-II.The springs are also accessible by small boat,although caution should be used. The lake and associated streams in the valley are spawning grounds for salmon,making the area popular with local sport fisherman.The springs are reported to be used occasionally for recreation by local townspeople. Vegetation in the valley is predominantly marsh grass.The adjacent valley to the north is drier and sometimes used as grazing pasture for livestock.There are numerous old military buildings in the area and are now owned by the local native corporation. Geology The valley is covered with alluvial deposits;beach deposits occur near the coast.Bedrock consists of the unalaska Formation,a thick sequence of coarse-and fine-rained sedimentary and pyroclastic rocks intercalated with dacitic,andesitic,and basaltic flows and sills,cut by numerous dikes (Drewes and others,1961).Dikes near the springs site generally trend west-northwest and were found to be feldspathic basalt porphyries. Several northwest-trending normal faults occur in the area.A fault immediately north of the springs site has a strike of N.50°W.Another normal fault located south of the valley has a similar trend and is thought to be Recent (Drewes and others,1961). Spring characteristics The thermal springs emerge from the alluvium into shallow pools located at the base of the eastern valley slopes.The main pool is about 1 m in diameter and has a maximum temperature of 36°C.Discharge from this pool,measured at 64 lpm,joins a small wam stream with a temperature of 15°to 20°C and a flow rate of about 40 lpm.The combined waters in turn flow into a second 1 m-dia warm pool measuring 20°C.The warm waters eventually flow into a marsh that drains towards the valley lake.Both pools are floored with organic muck and exhibit slight gas bubbling. During the fall of 1980,two shallow test wells were drilled into iron-stained sediments on the southeast shore of the valley lake.The work was done by Dames and Moore Associates under supervision of a DGGS geologist (J. Reeder,pers.commun.).The wells were spaced about 200 m apart and were located about 500 m northwest of the springs site.Both tests found a warm-water aquifer system in black sandy soils at a depth of about 13 m. Bedrock was encountered at a depth of about 17 m.Water flowed from well 1 under artesian pressures at 180 lpm and a temperature of 50°C;well 2 showed *°lpm and 44°C.A Table 20 gives the chemical and physical properties of thermal waters sampled from the two wells during artesian flow and from the main pool at the springs site.All three waers have chloride and sulfate as their major anions and sodium and calcium as the major cations.Compared to hot springs sampled elsewhere in the Aleutians,the thermal waters at Summer Bay are notably low in Silica.However,the systematic variations of water chemistry vs measured temperatures at Summer Bay indicate that cold waters mix with thermal waters (table 21).Except for Ca/Mg,the three waters are nearly identical in each of the various ratios,indicating that the waters have a common-parent thermal water and that it undergoes varying degrees of mixing with cold waters.The colder samples are generally more dilute than the warmer samples,which suggests that the cold-water fraction itself is very dilute with respect to the major constituents and that the chemical constituents present in the sampled waters are mainly derived from the parent thermal water.The variation in magnesium content could be attributed to varying degrees of reequilibration of waters in the shallow warm-water aquifer or perhaps to the derivation of magnesium from the cold-water fraction. Although the above evidence indicates most of the constituents present in the waters originated from a deeper parent water,the wells showed marine sediments at shallow depths.The possibility that some or most of the constituents present in the waters originated from interaction of wam waters with these shallow sediments cannot be discounted. Reservoir properties The test wells drilled at Summer Bay documented the existence of a shallow warm-water aquifer ranging up to 50°C and located south of the valley lake. From the well log,the cap for the system appears to be a lightly cemented layer of "chalky clay”that occurs at a depth of about 10.5 m (Dames and Moore, 1980).Artesian pressure was probably provided in part by the surrounding cold-water hydrostatic head and by the bouyanc y of the heated waters.Bedrock was encountered after passing through about a 17-m-thick sedimentary sequence of coarse-and fine-grained sands and chalky clays,some of which contained shell fragments.Bottom cuttingsof bedrock from the wells were basaltic chips. Table 22 summarizes the application of silica and cation geothermometry to Summer Bay thermal waters.Even with the assumption of equilibration with quartz,the silica geothermometer predicts a relatively cool,deep-reservoir temperature of 60°to 86°C.Although the low silica contents of these waters may be due in part to reequilibrium in the shallow warm-water aquifer,the linear trend with temperature of silica and several other constituents indicates that the low silica is probably due to extensive mixing of cold surface waters with ascending thermal waters.Such mixing could also partially explain the ambiguous results of the cation geothermometer. If mixing is assumed and the linear trend of the silica vs enthalpylline is extended to its intersection with the quartz solubility curve (eg. Truesdell and Fournier,1977).the deep-reservoir silica-content and temperature may be as high as 150 ppm and 160°C.Extrapolation of the linear chloride trend of the surface and,shallow aquifer thermal waters to 160°C suggests deep-reservoir chloride concentrations may be as high as 5,000 ppm. Comments The chemistry of the waters and the location of the thermal site at the floor of a drainage basin indicate mixing of cold surface waters and deep ascending thermal waters occurs in the shallow subsurface warm-water aquifer. Steep normal faults are located near the site,suggesting deep-seated fractures are conduits for the circulation of meteoric waters.The waters become heated at depth and eventually emerge at the floor of the valley.The trend of the faults is in the direction of convergence of the North American and Pacific tectonic plates in this section of the Aleutian arc. Silica mixing models indicate deep reservoir temperatures may be as high as 160°C.Chloride-enthalpy analyses suggest that the thermal waters are briny with a chloride content as high as 5,000 ppm.Future exploration programs at Summer Bay should be designed to locate the fracture system(s)that are supplying the hot geothermal brine to the shallow warm-water aquifer. Table 20.Chemical composition and physical properties of Summer Bay hot spring and wells 1 and 2 (all chemical analyses in mg/1) Characteristics Hot spring S105 18 Al nd Fe .0.09 Ca 202 Mg 1.0 Na 150 K 3.0 Li 0.03 HCO3 73 SO,245 Cl 404 F 0.22 Br 1.25 I 0.00 B 0.5 H2S nd Sr 0.94 pH,field 6.98 Dissolved solids 1099.1 Hardness (mg/CaC03)509.68 Sp conductance (mno/em at 25°C)1810 T (°C)35 Flow rate (lpm)64 Date sampled 7/18/80 nd =Not determined. Well 1 35 nd 0.10 460 6.34 332 6.49 0.16 nd 528 923 0.44 3.02 0.19 0.5 nd 2.0 nd 2297.2 1177.3 3850 50 180 9/26/80 Well 2 25 nd 0.14 372 10.3 276 5.45 0.12 nd 423 741 0.40 2.65 0.00 0.5 nd 1.52 nd 1858.1 970.5 3000 . 44 30 9/27/80 21.Ratios of chemical constituents in Summer Bay thermal waters Thermal spring Well 1 Well 2 0.37 0.36 0.37 0.007 0.007 0.007 0.50 0.50 0.50 0.61 0.57 0.57 202 73 36 50 51 51 1.35 1.39 1.35 Table 22.Summer Bay thermal-water geothermometry (all temperatures in degrees Celsius) Thermal spring Well 1 Well 2 Surface temperature (measured)35 50 44 Cation geothermometers Na-K 109 108 109 Na-K-Ca (1/3)92 95 95 Na-K-Ca (4/3)24 35 33 Silica geothermometers Adiabatic 60 86 72 Conductive 60 86 72 Chalcedony 27 55 40 Cristobalite 11 36 23 Opal -49 -28 -39 KEY Thermal Springs Bechoref ake 34 of.1.Atka West 18.Unimak 2.Atka North:19.False Pass 0 100 200 300 3.Korovin 20.Kenmore t 1 ; 1 !Pilot Point_ 4.Kliuchef 21.Egg Ieland Kilometers , 5.Seguam 22.Frosty Peak 6.Chuginadak 23.Cold Bay 0 50 100 160 200 . 30 7.Kagamil 24,Emmons Lake L !1 I !.Port Heiden 8.Geysers Bight 25.Pavlof Miles 9.Hot Springs Cove 26.Balboa Bay 29. 10,Partov 27.Port Moller 11.Okmok 28.Stepovak Bay c<] 12.Bogoslof 29.Port Heiden Port Moller Ke 18.Glacier Valley 30.Surprise Lake 14.Makushin Valley 31.Mother Goose 21 15.Summer Bay 32.Mt.Peulik 25 tt was16.Akutan 33,Ukinrek ;24 {P28 17.Akun 84.Gas Rocks Cold Bay a 26 23 O (on) c)esfor(PA)oO,Sand 7 ¢&, e Sampled,1980 ae Point °oo i , °Not Visited,1980 King Cove 4 Not found,1980 Activity diminished *Villages .Unalaska 2 a 54. 3 5 "u ak I Atka Atka =»royMts:mane * 6 NikolskiIs.i QR Seguam Location Map Is. ehomif.ip j Ke pared f Lip}SPA Ye 4 ry (0.Ales Lie an ra BoclienS Lp he ' Ake NORTH ISLANDUNALASKA MAKUSHIN VALLEY MAKUSHIN 'VOLCANO 2040 m. Makushi :.win 1 sf 'wo <--3 Dutch HarborCinderConea, 0 5 10 15 "20 0 5 lo 15 L 4 1 L J t 1 j j Kilometers Miles GENERALIZED GEOLOGY Adapted from Drewes and Others (1961) er Qt 23) Surficial Till Deposits Pe cae =**Qi rs E-Qe =]'iat E- Glacial ice Eider Point Basalt Includes olivine, 2 pyroxene basalt and rhyodacite porphoriecs. ere were '.”.;re:he Qtms.4<aPheLa Makushin Volcanics Basalt and andesitic lava,pyroclastic rocks with minor sedimentary rocks,AUVILYILAUVNUALVAdSVrseeweaee\y >+*Ter 4 Tus++g +ne =ke Granodioritic Gabbronic Batholith Granodiorite,diorite and minor Unalaska Formation Slightly altered andesite and granitic facies,gabbro border facies,basalt and sedimentary rocks 9 Springs O Fumaroles &)>Caldera Faults Dikes AUVNAGLVNSAUVILAALGeneralized Geology of Northern Unalaska IslandFig.Py ' ¥Sy ipesGTS OSs oats OnTASweIANS IYORES,ogaySeotheyAEEi*)ieahZEST|]Dutch Ha S Ope Soap es . ANG DEED TIN amare a Sk.3 Penn Re a ion LZ Ps .PoBes vay -a an r . .a pis ;s >="<Sai int g = 1 7 D7 7576 a do heSean|SESYNMines AHTRNSiatah\WS a BSS =NaNES 4 MAKUSHIN "+VOLCANO A L 'Area of >}r Numerous -.ne 'Fumaroles. :@ Spring MILES OO Fumaroles Hot Ground 2 3ove"3 KILOMETERSro Li> 2)=4 Platform below Fumerole Field --Drainage 3o)Seeps ©Steam Vents *Dry(OJd Spring Location)- Snowfield, August 1980 50 100 150 =.200 i \!| Feet I !i ]J ni Meters bed tream \o 68 oot a Seeps All Temperaturee in °Cae=w 65°All Flows in liters/minute gees MC =ANI Conductivities in pmhos/cm.o ." S Multiple 7 o°Sources 'a 25.4° To Glacier River KanbanFey 24.Betatl al Glace Valleg Ad SPhingsom Umalake Island So ff itz BEOCIT CHARACTERISTICS AND DEVELOPMENT -FEASTB8itttTY OF ALASKA'S GEOTHERMAL RESOURCES--WEAE-EMPHASTS-ON--THE -MARKUSHEN-VOLCANO_REGEON-O F-UNATASKA_-ISLAND- )Mr.David Denig-Chakroff =|:__j Alaska Power Authority 4 oa /lorCe.334 West 5th Avenue vA J C&a Anchorage,Alaska 99501 CL /n a ,;yeeI/Dr.John W.Reeder , Bask Division of Geological and Geophysical SurveysntBox772116AeeRiver,Alaska 99577>ssovcrio Any plans for geothermal development in Alaska should be based on the nature of the resource,and on the economic and legal feasibility for development of the resource.Both of these factors need to be favorable for development in order to have and/or justify development in a truly capitalistic system. THE RESOURCE AND DEVELOPMENT FEASIBILITY 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 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,orsmallinsize,and usua]ly is within 4 miles depth.Geothermal fluids canalsobeclassifiedonsabasisoftheirgeochemicaland/or geophysical character.For example,geothermal systems can be dry-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 dominated systems are for all practical purposes restricted to the high temperature resources.The recognition of these 'contrasting types of geothermal resources provide 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 -ssgeothermal 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 dwellings,bath houses,and greenhouses (i.e.,Bell Island,Chena,Circle,Goddard,Manley,Melozi,Pilgrim,andTenakeeSprings).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 exist or not at shallow depths in the region.Such ground-water bodies might exist in large sedimentary basinsthatoccurthroughoutalargepartofAlaska.Smaller ground-waterreservoirsmightalsoexistinfracturezoneswithinmetamorphicand igneous(plutonic)-rocks that also occur throughout the State.If fractures extendee2hneefenHeehakATkDRthanthanuniintatsRaMmRRMATRRtA |NEEDaes|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 convection in fractures related to igneous(plutonic),some metamorphic,and very limited sedimentary rocks (Waring, 1917;and D.G.G.S.,1983).; Typically,the regions of deeper hot-water reservoirs where moderate temperatures can occur will be overlain by shallower,cooler aquifers that contain water slightly under boiling temperature.Such shallow aquiferswouldbemorelikelyfoundif.shallow sedimentary rock exist in the region incontrasttonormallydensermetamorphicandplutonicrocks.At Pilgrim Hot Springs near Nome,a shallow aquifer with temperatures near the boilingtemperatureoccursinsedimentaryrock,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 produck{over 300 GPM artesian flow at 194°F with existing wellsthatweredrilled'by'State funds.Based on the temperature gradient of these wells,it has been interpreted that the deeper reservoir exist at a depth ofabout5000feetandatatemperatureof302°F (Economides and others,1982). Such shadlow geothermal resources (i.e.,normally at depths of less than 500feet)"ts-often accessible by typical water-well drilling rigs as opposed tothedeeperreservoirs(i.e.,normally at depths of 4,000 to 6,000 feet)with higher temperatures.The moderate temperatures at the deeper reservoirs are attractive,but the ultimate 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.Additional information on drilling requirements for geothermal wells may be obtained from the Alaska Division of Oil and Gas.* Large-scale geothermal electrical power development projects require temperatures normally in excess of 392°F for efficient operation.Such hightemperaturegeothermalsystemsarealmostexclusivelyassociatedwithigneous 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;and at Larderello,Italy are all associated with young (i.e.,less than 1 million years old).igneous systems of a particular type,that is those consisting ofarhyoliticmagmaatshallowdepthsthatWas-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 amajorityofAlaska's.55 plus active volcanoes,which are located in theAleutianarc.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.Never-the-less, Alaska's andesitic volcanoes may be underlain by "trapped"magma that has risen from great depths.Such magma bodies might serve as a significant heat source for large moderate-temperature and with luck maybe even high-temperature geothermal systems.| MAKUSHIN VOLCANO REGION OF UNALASKA ISLAND The Makushin Volcano region of Unalaska Island is of no exception.Prominentfumarolefieldswereobservedinthisregionin1980(Reeder,1982),which 5 Tt Fe tatewa ta have the Alaska Power Authority initiate exploratory drilling in the summer of 1982.The result was the discovery of a fairly large and hot water-dominated reservoir,which appears to be at a temperature slightly less than 379°F and at an estimated volume of at least0.7 miles cube of water (Economides and others,1985).Although theexploratorywelltappedthereservoirbymeansofalargefracturewithin plutonic rocks,which are common throughout the region for both plutonic andvolcanicrocks(Reeder,1985),the actual reservoir is probably located immediately beneath the Makushin volcanic pile within fairly permeable brecciated rocks. <-Dave pies -tnsery your feasibitity input CONCLUSION As with many other resources in Alaska,geothermal exploitation is hindered by the remoteness of the site from Alaska's population centers and by the small size of Alaska's energy markets.In the case of large-scale geothermal development,the significant up-front capital cost in the range of tens to hundreds of millions of dollars,which include the dry-well risk associated with the initial well-drilling phase,is another disadvantage.Development on this scale is beyond private individuals or even most venture-capital companies.In addition,any reduction in petroleum prices will in general have a detrimental effect on any geothermal development in Alaska beyond that of recreational direct utilization. Never-the-less,Alaska has some of the largest geothermal resources in the United States (Muffler,ed.,1979).Alaska also has geothermal resources that could lend themselves to large-and small-scale hydrothermal energy development.For example,geothermal power developers around the world are presently watching the progress of the Alaska Power Authority geothermal project on Makushin Volcano of Unalaska Island. "REFERENCES Division of Geological and Geophysical Surveys of the Alaska Department of Natural Resources,compiler,1983,Geothermal resources of Alaska:National Oceanic and Atmospheric Administration,U.S.Government Printing Office,1plate. 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,StanfordUniversity,pp 25-30. Economides,M.J.,Morris,C.W.,and Campbell,D.A.,1985,Evaluation of the Makushin geothermal reservoir,Unalaska Island:Proceedings of the Tenth Workshop of Geothermal Reservoir Engineering,Stanford Geothermal ProgramSGP-TR-62,Stanford University,in press. Muffler,L.J.P.,ed.,1979,Assessment of geothermal resources of the United States -1978:U.S.Geological Survey Circular 790,163 p. Reeder,J.W.,1982,Hydrothermal resources of Makushin Volcano region 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 BLulletin,in press. Waring,G.A.,1917,Mineral springs of Alaska:U.S.Geological Survey Water-Supply Paper 418,114p. [hiS 18 Uosy qeras St.SITU,Obie to Shara tn it by [0m Ae o fil'Le phe viene»yy Sect,curthiog tw?figures Dian.Vans dara pea!@,Re tuen we foren -fo "Reactor”Ay SO%o (TbseeaTheGeothermalResource of the Remote Makushin Jj Aleutian Islands."7.redtopy Ph Ss.Sersacl to oTcano Region of the J.W.Reeder (1)|D.N.Denig-Chakroff (2)|and M.J.Economides (3)we mPa CIOPEIOEF fey Q)oy ace oaical ,7-028 LAK FCA,Alaska Division Geological and Geophysical Surveys,Pouch 7-028,b.Croog Anchorage,AK 99510,U.S.A.:me {CrassJSLowaf (2)Alaska Power Authority,334 W.5th Avenue,Anchorage,AK 99501,U.S.A.€eSoy t- (3)cu ttly ex utDowel1-Schlumberger,Marble Arch House,66/68 Seymour Street,London oe. W1H5AF,U.K.Cred DM,Ceiptiour ABSTRACT Shaukd fo.Cisted i 7) yo f|Geological,geophysical,seochenicays and wel]flow-test data (from-a-singte "Sing(6 Qk volume ;nf a."|exploratory-weH )suggest a 13+km3,640k dominated reservoir at slightly less -Cotthan195°C beneath the Makushin Volcano caldera that reaches a depth of about ot periAAyaonthenorthern,eastern,and southern flanks of the volcano as reflected by Chay :.Ys 4.4+km..Through numerous fractures,this reservoir is presently discharging taenumerousfumaroles.Rising gases are also escaping directly.to the surface VV tLAY,(an through the caldera as reflected by the largest fumarole on the summit échy "y acaldera..actu al A pregoeSee 516/397 e myo ty,-Lis Based on extended flow testing of scorn ete ne lower eastern flank of Makushin Volcano a full-size production well'at the site would be capable of producing 7 to 12 MW of electric power,which would be sufficient to meet the present and projected power needs of the Unalaska/Dutch Harbor community.Reservoir analyses indicate that this level of production could be maintained for several hundred years. A economic analysis has been conducted to determine the feasibil- ity of developing the resource to meet the electric power demands of the Unalaska/Dutch Harbor community.Thgs analysis was based on,Bae stics 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 economically competitive with a diesel power system on the island.(A-detatied feasibility study of the project - shou oncentrate Cc 516/397 NOMENCLATURE T =temperature,degrees Celsiusp=pressure,Gen eo,(kara?)(Psi (1H |?)V =volume {we]r =recovery W.=initial fluid-in-place(kd )@ p =cumulative mass produced .(kg}t =total compressibility,((kg/em2)7?) =rock compressibility,((kg/em?)74)"-eZ=fluid compressibility,((kg/cm?)74)LK 516/397 © INTRODUCTION KA 2 :.'BET gah PIT dua 808. The Makushin Volcano region of Unalaska Island,which is located in the eastern Pare onthe Aleutian Islands of Alaska,has been the site of a-Sterteuch-YyeaofcpiaslgAen exploration program.Following extensive geological,ee cohscteat,geochemical,and temperature wn investigations of the Ge P avy xte Te A ASK ge ar ppoowes HES 4adwhichencountereda19564water-dominated reservoir that has-a 2.04 to 2.17 one -p PP POrent LM 4 nated geothenmaT\,(kg/hr)/(N/me )productivity index."4 Bvery large,water--dominated geothermareservoirexistsintheMakushiniatcaneregion. vcna >\Sie City of Unalaska,consisting of the adjacent towns of Unalaska and Dutch'0!Harbor,is the only community on Unalaska Island.It is situated at thenorthernendoftheislandonawell-protected bay (Figueg 1).Unalaska wasanimportantcrossroadsforshippingandtradeduring'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 location for a major naval base during World War II.Since that time,the fishing and crabbing industries have been the mainstay of Unalaska's economy.Such industries, along with the nearby potential for Outer Continental Shelf oil,gas,and mineral production,will probably play an important part in Unalaska's future economy.(Ate ast 516/397 The first objective of this paper is to develop a geo hermal model for theiwqovmésOwMakushinVolcanoregion.This is based on ,which in addition to general geology includes geothermal surface manifestations,faults,well v EL SS srea ----. nna suit wat SUNALASKA BAY-y memo es ©wand oranneeaZIT]SUMMER BAY ore q IT MAK DUTCH HARBORta ©&Mi oe C4 . =+h eteAPPAPAPPP eS on O it |Yn(0)exit aves UNALASKA€wat @ THERMAL GRADIENT HOLES sO GEOTHERMAL RESOURCE WELL Figure 1.Map showing the location of the Unalaska geothermal project.) oud capbpns dy,ote516/397 tests,gravity,and whole-rock geochemistry.The second objective is to make an estimation of production well potential for commercial operations at theexploratorySiteof_expieratinn well ST-1 on the lower eastern flank of Makushin Volcanog (Fisaeot The third objective is to present a preliminary economic analysis4 of utilizing the Makushin Volcano geothermal resources to meet the current an future power needs of Unalaska.The economic analysis takes into account th characteristics of the resource,the deliverability of the reservoir,the logistics of development and operation,and the demand of the power market. 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 (North American Plate)in a northwest 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 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 that have intruded the Unalaska Formation,and a younger group of unaltered volcanic rocks (igure 1).The region southeast of Makushin Volcano consists mainly of rock exposures belong- ing to the Unalaska Formation,whereas unaltered volcanics make up the Maku- shin Volcano and most of the rock exposures to the northwest of a line extend- 516/397 'q:©5 10 Km Seo 166°30° a f..cat fitees)54°]ee 1 Stee 7 Unolesko Brunop Pt Boy |Ti 08 PTT eet Cona440+Mosverr Vole,0%fs +Moagene "vowone r-53°4§° MVoreustin Eoy alLA SS ALASKA Map Symbols oy,aes (USA)7 Fault:dashec where approximate Sty PeFumarotefield'nsy ge ae Warm and/or hot springs a aeRecentvolcanicventrt Caldera oF \-map location (Northern part ofUnalteredvolcanicrocksUnateskaIsland) Plutonic rocks Unaleska Formation Figure 2.A simplified geologic map of the northern part of Unalaska Island, 'after Drewes and others (1961)and Reeder and<otHers {19858}.The A-A*line ig the location of the complete Bouguer gravity profile in figure 5. 516/397 ing from Pakushin Cone to Table Top Mountain (Frome 2).¢ The Unalaska Formation is upper Oligocene to upper Miocene (30 to 8 mybp)as based on fossils (Lankford and Hill,1979;and Drewes and others,1961).This formation in the northern 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 of these plutons yielded ages of 11+mybp (Marlow and others,1973)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 (Fig.2)that erupted about 8,000 ybp (Reeder,1983).The most recent eruptions of Makushin Volcano occurred in 1938,and 1951 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 from the immediate Makushin Volcano region.Except for Pakushin Cone, 516/397 SE Pa LEEsRayeas'a,Saas.a,qm:eek a Figure 3.A view of the 2.4 km diameter Makushin Volcano caldera as viewed in a east-northeast direction on February 27,1982.The steam cloud near the far center of the caldera is from fumarole field no.6. 516/397 Wide Bay Cone,and the Point Kadin cones,the volcanic cones of the area have 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 Makushin caldera eruption event (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 disco- vered on the flanks of Makushin Volcano (Reeder,1981 and 1982).Of the nine major fumarole areas Foysp 2),only fumaroles no.3 and 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.The largest fumarole field is no.6,although the 1980 discovered fumarole no.3 is the largest fumarole field on the flank of Makushin Volcano. Some warm and hot springs exist in or at lower elevations to the fumaroles. These springs dre rich in HCO.SOy>and Ca.They have apparently originated from meteoric waters that,after infiltration into fractured rock,have been heated by ascending gases and/or by conduction from wall rock (Motyka and others,1983).The 3He/*He compositions of these rising gases as determined by Motyka and others indicate a definite magmatic influence.The fumarolic activity is evidence for at least a shallow vapor-dominated zone beneath each fumarole.- 516/397 FAULTS Faults,mostly near vertical and having small displacements,are found throughout the region.In a few cases,faults have been found trending directly into Quaternary volcano centers such as Pakushin Cone,Sugarloaf Cone,and even active Makushin Volcano (Reeder and others,1985b).The location of nearly all of the fumaroles appear to be at least partly con- trolled by faults (igure:2).For example,an east-west striking fault and a N 50°W striking fault have been recognized as intersecting at fumarole no.1(Reeder and others,1985c;on fia 1). Many of the fractures of the northern part of Unalaska Island reflect orienta- tions expected for a regional stress caused by the subduction of the Pacific Plate,namely an approximately N 50°W striking set with approximate corres- ponding N 05°W,N 40°E,and N 85°E sets MY Another observed N iki sh Ae68°W striking set *eecbeencexrbainerzthyetertemassbeing caused by the late Miocene rotation of the northern part of Unalaska Island.These fractures,1S en J before this rotation,would have had the expected N 50°W strike.AT qe «wettestpriczivg Ap wee TEST)W(r Three temperature gradient holes were drilled in 1982 and one in 1984 to depths of up to 460 mon the lower flanks of Makushin Volcano as indicated in Figueg 1,and encountered temperatures of up to 195°C.(These holes were, dritted-by-RepubticGeothermal,Inc underethe-Ateska Power-Authortty tone -516/397 -These holes and their temperature gradients are described by Isselhardt and others (1983a),and by Republic Geothermal,Inc.(1983 and 1985). ch rst fractured mafic crystalline rock (gabbro-norite as defined by Queen,1984)atqu,205 m depth and then encountered a water-dominated zone at a large fracture,5 Ry F 4 ::: \gupe 4)also in mafif crystalline rock,at 593 m depth.In fact,there,'abukyrt ertdrillstemdroppedfreefortheee-feet>(wHdt3}when the drillbit encountered0).\\fly this large fractur (Fradequeteprossure-eeqrTpnent-ENo Ue -THTE Ofte time=ferCyacaniadeneteronerothsoneproventedeany-rtgorUuS-WeTTLEEfo(Campbell and Economides,1983). . o Figure 4.August 17,1983 view of the initial opening of the Republic Geothermal,Inc.exploratory well near fumerole no.1 for its first flow test. 516/397 won The 1984 test of ST-1 consisted of two flow periods of approximately 33,000 lb/hr and 63,000 1b/hr each.The test rate/wellhead pressure/bottomhole pressure history is shown in Figuge 5.The first flow period lasted 15 days, z 2 3 oc 7M 3 :4 a99 =:63000 Ib/hr rete w :re OF 498 <Hy +_ -3 WHP = 3 "ee a - SO+t 2 =.4497 w a 6h = w 4 | ------af--------]R x ---}496 Wwnees2onBHP,- yj 33000 Ibfwrate i FOO SOOOOO OS eeeee t-7 x 4 7 WHP uw x 30++495 Oo x a = w 20 -f +494 e 3 LOW RATE HIGH RATE FEZz:2.07"Nazzle 3.0”Nozzle '4 =wt 1.78"Orifice 3.4”Orifice +493 0 ---492 0 5 10 15 20 25 30 35 40 TIME (deys) Figure 5.Makushin ST-1 flow test,July-August,1984. 516/397 smoothly .with thetwo flow rates being maintained at essentially constanten.. Lit e $4 }crt thetr respecttrve-testperrodssa. a Prior to the initiation of flow from ST-1,a static temperature Pe of thewoweIbore(1astebtntmedsantaie}and a static pressure profile 4%?obtainedemmy wulysts as shown in Figuuae6.These temperature and pressure profiles have TEMPERATURE IN DEGREES © 14¢145 150 155 160 165 17¢175 160 1865 190 195 200 °TT T 0 |'|||' if:|50 bn pnp eas ;rn on Met)fog Po i ;'7 . 100 ------f$4+-4 wo pet £00 |:|i , ;. -150 ;Be fe ep 180 200 -:we Bp ee ee ee 209 | 27),: : :a= s pe ce or neces oe eee wee ee ee 250ss250ae-4 .he tenn pene ieee ee Pa ieee gee eg 8Z300:.+::20 e !'.'oN 'nee eee eee eee eed eee ee eee °wk ee ee -___f s5Ww350otint250 ot N 400 :pot te 4 +41 490HE|\ |':'a ::450 oa ee too BN eb ho . 'i '| i :'S .!i -+-TEMPERATURE it550[|_.+-pressure ; : ;fof |600 te]3 6 9 12 15 8 ef 24 27 PRESSURE IN KG PER SG CM (GAUGE) Figure 6.Static temperature (July 3,1984)and pressure (July 4,1984)in ST-1. 516/397 slightly different values from what was originally reported by Economides and others (1985)because of data collection and analysis complications as ex- plained feaesst by Republic Geothermal,Inc.(1985).These surveys indicated that the well,which is located at about 360 m aysy'(above sea level),has asteamzonewithavapor-liquid interfac€at a depth of 250 m (110 m a.Syl.). Below this depth is a liquid zone,which increases to a maximum temperature of 197.8°C at a 457 m depth,then declines slowly to a temperature of 195.0°C at TEMPERATUHE IN DEGREES Cthebottomofthehole..ne 140 145 {50 158 160 i16€i:70 175 #160 «1:85 «#19 #195 200 00'T,:TT :|: :::. (4 \re | 50 oo Spot a re MT)i -'j H \ee 100 ro iB A.copes aeh aot 100 \' $69 --------_oe ---------4 450 on ae=250 250 rEs Z 300 |300 =350 (350 £00 800 450 450 t 500 500 550 -+-TEMPHRATURE an -«-pREssipe i "Tr 550i. T .:;.soo LLL 1 |tor tL NI,,, Q 3 6 9 12 15 18 24 24 27 30 33 36 Figure 7.Flowing temperature (July 6,1984)and pressure (July 6,1984)in ST-1. 516/397 After flow was initiated fnadnadets)the well stabilized at adtaom Any SG ,T of about 33,000 lb/hr and this condition was maintained ; During-this=flow-perted-the.pressure.poalwas left at the bottomofthe-wetl flow rate (dy D4G-feet>ContThtousty recordingbottomioTepressure,excépt"for-the*times when-wet Iborepressturé”and tenpera ture=prof+t esawereobtainedser Fiowing™ ,ater colleetespressuresart-temperatire-profidesewerenabtainedeoneduty 6.The are sSLOWR re TRGTPELT om fas econd.set-of-pressure-temperatere-prot tres-were.obe YEMPERATURE IN DEGREES €Ave 140 145 150 155 160 165 170 175 180 185 190 19&200 *(3 0 TTF I 9 descenbed *OG . 50 pene ee -a ns mT,by Econom As Figure 8, ST-1. 516/397 OEPTHINMETERS100 | 200 250 300 350 400 «50 500 "$50 600 ”i 4 -+-TEMPERATURE =i i "5|__|weed LS: -4-7/PRESSURE |-_59 '}1 Wy i ;:.t xaee 0 3 6 9 12 15 48 21 24 27 30 33 36 PRESSURE IN KG PEA SG CM (GAUGE) aud otGers|198s) Flowing temperature (July 20,1984)and pressure (July 21,1984)in eTJury dich overla oY}July/@ profiihofotoobgeryédALLheheayspttheWhy, Following HyeKn ange in the flow to ®higher rate of 63,000 1b/hrcme sure-teelwas-againteft at the bottomof thehole-eottinucuslrecesdinge <» Ofr additional ydrawdownwasobservedduringfp19-day high rate period.The well was >207 ont shut-in on August 8,1984,with the pressure tool hanging in the well at bottom.The pressure tool recorded buildup data for the next 17 days,showing Tess than Ghe-pst 9}increase in bottomhole pressure.5/5 2'Cm-ul Produced fluid enters the wellbore at the bottom of the wellg/1,946-1,949feet)at a temperature of 195°C.The fluid from the producing horizon rd nok og esult iV approximately 16%vapor and 84%liquid by mass at usable wellhead pressures.It measures 7800 ppm total dissolved solids.These waters were,moderatet Saline,low-bicarbonate waters at a static bottomhole pressu (es of 3.4 x 10 N/me gage. It appears that th ssure drawdown during the low-rate flow period was on the order of one psig while the pressure drawdown in ST-1 during the high-flow Thuratewasontheorderoftwopsi.ductivity index derived from "31,000-33,000 Wh/hr/pst.the two flow periods equal 516/397 204¢-AT(hspw/,,2) hese 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. After shut-in,the wellbore re-equilibrates to its 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 essen- tially only one inflow point,however,the pressure buildup was measured opposite this point the re-equi libration of the wellbore fluid density should have no effect on the accuracy of the measured reservoir pressure.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.\Y eC Vey CDES | Reserve Estimation Using a Material Balance Calculation os / 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 initiating step is an expression providing the isothermal compressibility.oo c=yt (1) Assuming that the total compressibility of the system is constant,Equétien 1 may be integrated:id 2 cAp (2) and because the recovery in terms of reservoir volumes is defined as: 516/397 1 ,(3) VI Eqs. then a combination of Bewattons2 and 3 results in: 21 echP=-1Thecumulativeproduction in sen of reservoir volumes is,of course,Vo-Vyand,because the fluid is considered incompressible,the ratio aa S WA (4) OE}cf" which is the ratio of the cumulative mass produced to the initial mass-in-place.Hence,Equetdos4 becomes:fi® WP=g(C4P)_4 (5)fOfthevariablesinEquator5,Wo is the one known with certainty.In thiscaseWisequalto:°P14,G4 28 637W,=335606-x 15 x 24 +635800 x 19 x 24 =406KTEtbs:7 reflecting the two flow periods.l x4 X19 ley The variables contained in the exponential expression consist of the totalcompressibilityofthesystemandthefuiaeasdreservoirpressuredropobservedduringtheflowperiod.In this system,the total compressibility is the sum of the individual rock and fluid compressibilities.wh)Pate Ch =C+Cy SI AG (6)t Water compressibility is normally taken as stone pst,while the compress-Lild ibility of the rock could reasonabl@\range between and oto 0)psi7?,depending on the lithology and the elasti¢ity of the geologic features. 107°psi7!,This value will be used here with the knowledge that it could be somewhat higher or lower. 516/397 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 result- ed in less than on psi pressure gain.both tests indicate an extremely large permeability-thickness product which is consistent with the small pressure differences observed.The total average reservoir pressure drop is assumed to be roughly one psi. Using Equation,5,the initial-fluid-in-place may then be calculated:PBS ecw Goof(6 x 1076 -1viejaxee.Given the uncertainties inherent in this calcu- lation,the vajyue of "W"can be considered order of magnitude only.Assuming an approximate \average density of 1.09/en°for the reservoir fluid,such areservoirmasswouldequatetoawatervolumeofabout3.1 km>. pre"keGRAVITYS- Unalaska Island (Reeder and others,1985a).Figure #shows a complete BouguergravityprofileacrossMakushinVolcanoaslocatedinFicoee2bylineA-A'.6 Based on two-dimensional modeling,the dense (2.8 gm/cc)mafic crystalline rocks,which are exposed just southeast of Makushin Volcano (Figaee 2), f A total of 155 gravity stations have been obtained for the northern part of underlie the entire region Mae-gs-ghet asst Biel The only . ( area where this dense rock might not be continuous would be along a linearynortheastorientedgravitylowthatpassesdirectlythroughtheMakushin caldera.This gravity anomaly has been interpreted by Reeder and others as a northeast oriented fracture zone within the crystalline rocks that has been covered by Makushin volcanics. The most prominent gravity Tow occurs directly over the caldera of Makushin Volcano AfgedenB nd othe eZ \aebar ants Fi ging ey Such an anomaly is probably 516/397 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 this region for containing a 3+km?body of water. 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 and others,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.].Makushin caldera may be modeled as a 2.1 gm/cc cylinder to a depth of 1740 m (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.In order to obtain a fit with the 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.:(Figuse J).S ig fp/ 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 porous material.If the bottom 2.62 km of this cylinder is actually saturated to 20%of volume 3withwater,then the Makushin caldera would contain about 2.7 km of water 3withina13.6 km region.This volumeof water is only slightly less than the 516/397 calculated volume of 3.1 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 convec- tive circulation systems.These generic systems,in turn,correspond to high temperature (greater than 200°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 rhyolite or dacite (McNitt,1970)./By contrast,most other volcanic and/or plutonic igneousaveaja®,occurrences that Lepssceatatnet high silicic melts do not have,associated . (L aege Z ,high temperature hydrothermal systems.) Rhyolitic and dacitic rocks are lacking for a majority of the 36 plus active volcanoes of the Aleutian arc (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 Norse owerans temperature geothermal systems. The Makushin Volcano of Unalaska Island is typical of such large andesitic volcanoes.The Makushin volcanic field is dominantly a tholeiitic province 516/397 3 (Fig B60).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 Miocene crustal rotations as previously discussed under the fault section could help encourage the rapid rise of such magmas.Prior to these rotations,most of the intrusive and extrusive rocks were calc-alkaline (Reeder and others, 1983c;and Figare -Following this crustal tectonic rotation,most of the extrusives and even some of the intrusive rocks were tholeiitic.Such deep- seated crustal rotations would be expected to cause dilation of some of the larger fracture zones in the crust,and thus would encourage the more rapid rise of ascending magmas.Once such magmas reach shallow depths,they can undergo shallow,closed system differentation (Kay and others,1982).The tholeiitic magmas show a Fe enrichment trend (Ficam 6),which is consistent with low-pressure and high-temperature crystallization in a large shallow magma body. 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 driving heat source for the Makushin geothermal system.Based on the gravity model,such magma would be deeper than 2.51 km b.s.1.immediately beneath the caldera but could be at shallower elevations beneath its flanks. 516/397 GEOLOGIC DISCUSSION A large water-dominated reservoir appears to exist within the Makushin Volcano caldera at a depth of TE to +km beneath its summit.Rising gases from this hot-water reservoir would be presently escaping to the surface through the caldera fill as reflected by the largest fumarole near the summit of this volcano.Through the numerous fractures,this reservoir would also bedischargingfluidstothenorth,east,and south,as reflected by the Corfe nimber fumaroles on the northern,eastern,and southern flanks of the volcano (fig.XN 1).Such fluids,as they slowly move along fractures within the dense mafic crystalline rocks of the region,may slowly gain heat by conduction from wall rock.For example,the highest static temperature observed in the exploratory well was 197,.8°C,and yet the inflowing bottomhole fluids remained at a constant 195.0°C temperature.This exploratory well,possibly by means of the recognized east-west striking fracture (Figees 2),is apparently in direct hydraulic connection to the Makushin geothermal reservoir.Nevertheless,the inflowing 195.0°C fluids have probably been heated by the massive crystalline rocks,and such fluids are probably slightly warmer than the main Makushin geothermal reservoir.Recharge might be occurring very slowly from the western flank of the volcano as well as from its summit region. It is possible that large quantities of hot water may also be located beneath the flanks of the volcano in fractures within crystalline rock,especially beneath its northeastern and southwestern flanks where gravity has suggested a fairly large northeastern striking rift zone.Indeed,fumaroles no.5 and no. t ' ,Cee7arelocateddirectlyoverthiszone,and they LILLIES the presence of at 516/397 least some fluids within this zone.Nevertheless,large quantities of andesitic and basaltic lava extrusions have occurred on both the southern and northern flanks of this volcano during the Holocene (Reeder and others, 1985b).Such large quantities of lava extrusion have occurred with no indica- 'AADISTANCE(km) 2F18t14t10t6tt -140 COMPLETE |BOUGUER | Regional _._.-__--GRAVITY-120 (Density 2.6) -(mgal) o Observed 100 L Po dd Sha RESIDUAL GRAVITY x --10 (magal) oe x Calculated [720\L 18 14 10 6 2 28 25)DEPTH (km) 2.8 o -6 DENSITY MCDEL (gm/cc) 7Figure7.Gravity profiles and crustal density cross section for line A-A'of Figguwg 2. ® 516/397 74-VOLCANOES T T T 7 T T T T T 1 2 3 4 FeO*/MgO Figure Fed.(total Fe as Fe0)/MgO0 ratio versus $i0,for unaltered volcan- ic rocks of the northern part of Unalaska Island as shown in Figure 1.The calc-alkaline (CA)and tholeiite (TH)boundry line is from Miyashiro (1974). Data is from samples that were collected by Reeder and others (1985c). 516/397 744 PLUTONS . -=NWiFeO"/MgO q Figure f.Fed”(total Fe as Fe0)/MgO ratio versus Si0,Miocene plutonic rocks of the northern part of Unalaska Island as shown in figure 1.The three samples marked with a P are from a tholeiitic Pliocene pluton of the Makushin Volcano region.The calc-alkaline (CA)and tholeiite (TH)boundary line is from Miyashiro (1974).Data is from samples that were collected by Reeder and others (1985c). 516/397 tion 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 recog- nized as originating directly from the Makushin caldera during its 8,000 ybp eruptive activity (Reeder,1982;and Reeder and others,1985b).This suggestS 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 ever introduced again into the Makushin geothermal reservoir,large phreatomagmaticeruptionsStedbeexpected.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 northeast 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 northeast striking zone. Well Potential The estimation of individual well power potential for commercial operations requires the fundamental assumption that an extensive reservoir can be repre- sented by the fluid properties,initial pressure,temperature,and productiv- ity 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 achiev- 516/397 ed,then wellhead pressure vs.rate curves for various commercial-size well- bore configurations may be generated and related to appropriate power cycles with some degree of confidence. The flow simulator used for this study was developed by Intercomp (1982)and bw heSw oe Eo,has beenused extensively by the industry for geothermal and geopressured wellbore flow calculations for several years.It is a vertical,multiphase flow simulator which incorporates treatment for variable well diameter with depth,heat losses,and noncondensable gases.The "nominal"commercial wellconditionsarrivedatauseesme=fottews+-or 47 owen LDAh(1185)wore 29 Initial Pressure =Aghpy at 1,949 feet i a okt Wr 195°C 379°F at 1,949 feet a Inflow Temperature Salinity 4,000 ppm TDS C0,Content 200 ppmProductivityIndex==32,500-tb/heépsi 2+/pe Gm 2) 13-3/8 or 16 inch Wellbore. Using these conditions,simulator-generated curves for wellhead pressure vs. flow rate were construct d for the two different "commercial"wellbore sizessfow?Cioohom/adte Aud vty BS(Figume $2).At a reasonably optimum wellhead pressure o a)(forpa 'generation from this resource),a flow rate of>t,250,00¢to >sa0e.000 Afr iswae$22 Lolere 516/397 set |tur mest OUA0 Zan wu to Les predicted,depending on wellbore size. AKAN8 PFOFigure\?Makushin commercial size well predicted flow rate vs.wellhead ¢)pressure.(Fow Econo mee amd 4 67 )18 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 approximat 13 miles 516/397 west of the City of Unalaska in a remote,rugged,roadless terrain.Access to the site from the city requires crossing a three-mile wide bay,traversing the 'N\ 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.SY In addition,weather conditions may be a serious impediment to development and \)operation.Although the average annual rere (38°F)at Unalaska is Neehigherthanmanyotherregionsofthistakare,heavy construction is generally PSslimitedtoafour-month construction "window"due to wind and snow conditions.\_) Even during summer months,when the average temperature is around 50°F,high <xwinds,heavy rains,and fog could impede construction,operation,and im maintenance of a remote power facility. POWER DEMAND The power demand of the Unalaska/Dutch Harbor community has been marked by large fluctuations 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 1,500 and the peak demand has fallen as low as 4+MW. 516/397 seuerk Unalaska is pursuing gegmeégahs options to diversify its economy,which could both increase and stabilize electrical loads.These options include develop- ing 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 indus- try may use Dutch Harbor as a staging area for offshore oi]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 smal]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 establishments and industrial users generate power within 9ptheirowndieselgenerators.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 provide <pretininany)10 at the economics of developing a geothermal power facility on Unalaska Island. Prior to design and construction,a more detailed feasibility study would 516/397 be required. This analysis used present value calculations to compare energy plans for Unalaska based on three possible load growth scenario hree 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 scenarios. 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 geothermal 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 th based on the actual reservoir characteristics,logistics of development and operation,and market conditions.Since the explorat Oy wel |is believed to have encountered a high conductivity fracture that communicates with a geo- thermal 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 analyzed 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 forrYntTaninjectionwor.Ee Becrotonic data indicate that geothermal effluent may be disposed of in surface drainage without adversely affecting 516/397 the environment.Consequently,the results presented here assume that rein- jection will not be required.Due to the remote location of the site,conser- vative 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.Finally,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 popula- tion 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 Tow growth scenario for the planning period.A moderate growth scenario 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 increase projected by Dames and Moore (1982)assuming a low level of bottom- ory eafishharvestandprocessingontheisland."ew 6 we be mer phistoric poputettor-tremts.For each growth scenario,electric load forecasts were developed for residential, commercial,and industrial users and for city services.Figured |'| illustrates the total electric demand forecast for each growth scenario. 516/397 13.0 HISTORIC FORECAST ,12.0 -4 . P 11.0 -a10.0 < 9.0 4 POPULATION(Thousanda)o°IAKT NN201 1.0 5 0.0 ott 441 a a ate a Ok 1965 1970 197 1980 1985 Lf 1995 2000 2005 YEAR. Q LOW GROWTH +MODERATE GROWTH °HIGH GROWTH Figure 13.Historic and forecast population trends 1965-2005 (Denig-Chakroff, --eee en 1985). 40 354 o e 30 4 Newt i 25 -4< ba fe ;20 + 8 HICH GROWTH SCENARIO a 154 16] Z MODERATE GROWTH SCENARIO ie]1040 LOW GROWTH SCENARIO 5 + Opeeeee 1985 1990 1905 2000 2005 ut YEARFigurexGraphshowingthetotalelectric demand forecast for Unalaska/Dutch Harbor from 1985 to 2005 (Denig-Chakroff,1985). 516/397 A diesel power system plan was developed as the "base case"to compare the geothermal power system plans under consideration.A diesel generator capaci- ty 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 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 power plans were analyzed for each of the three growth scenarigg.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 value 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 geo- thermal site were estimated at $15.473 million,including a 30%contingency factor.Diesel fuel prices were assumed to decrease by 4%(real)in 1986,to 516/397 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 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. ECONOMIC FEASIBILITY RESULTS The net present value was calculated for each power system plan.The optimum diesel,binary geothermal,and total flow geothermal systems (i.e.,those with the lowest net present values)are depicted in Figure 4a The optimum geo- thermal 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 the high growth scenario are a 3-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 acost-to-cost ratio (Figure 18).The analysis shows that the,cous idonedsystemscpusiergParemoreeconomicalthandieselgenerationforeachgrowth scenario.The most economical source of power based on this analysis was the total flow geothermal system which showed a 1.10 cost/cost ratio with a comparable diesel system for the low growth scenario and 1.25 and 1.68 ratios for the moderate and high growth scenarios respectively.Although the construction cost estimates used for the binary geothermal systems were considerably higher than those used for the total flow systems,a binary geothermal system also proved more economical than diesel systems for each 616/397 XKINannS00GeenSeenReGeesGnenGeloeSeeGeeSeemsGESSee| er eeeeeeeeeeee(euotrti)ANQIVA LNAS3ZUd LAN coe && 4s00 IvVKUaHLOgD 1s09198410 growth scenario. . ©Re re ae May Go.reszseolAsensitivityanalysiswasconductedtodeterminetheeffectofa4.5%dis- count rate and various diesel fuel escalation rates on the economics of the alternative power systems.The lowest fuel escalation rate analyzed represen- ted a 4%(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 analy- sis.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 low 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.ee eo CONCLUSIONS The most likely place for a large geothermal system as represented by about 3 km of water at4 ghtly less than 195°C would be within the Makushin caldera \\ f _-_---ny|9!y /at a depth of up to 4.4 km.Such hot water would discharge gases through the caldera fill,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 northern,eastern,and southern flanks of the volcano. tho at Phis isa Nery simpVstic modél ahd not one without flaws,4 Boe appear to bé the/only modex that fits the limited amount of data presently 516/397 -Bi tDht yo FVELGE.Most geothermal reservoirs in the world that are associated with Quaternary volcanoes are within caldera structures (McNitt,1970).The Makushin geothermal reservoir appears to be another that should be added to the list. hould be capable of one to two million Ib/hr rates.A material balance calculation indicates a theoretical electricity reserve sufficient for the needs of the island for several hundred years at current consumption rates. Although a preliminary economic analysis was conducted,some general conclusions can be drawn from its results.It appears that a geothermal powersystemwgsblnecompetitivewithadieselpowersystemonUnalaskaIsland. 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.Major factors affecting the logistics of development have also been ascertained.Factors that are not known with the same degree of certainty are the future load growth of the community,the projected esca- lation 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 516/397 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 (estemmercrmmn')analysis,a more detailed CcOoW MIG 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 ACKNOWLEDGMENTS Shartow)and ora5h Fre-authorsextend-spectat-thanks-to-the-peopte of-Unataska-for-thet con li nian: QUS-Stippert--ofer-perspectsuptathtcetnyestigattonr.Very special thanks is given to Unalaska residents Abi &Jim Dickson,Kathy.&Bob Grimnes,Nancyneykp Unalaska/Dutch Harbor. Gross,and the Currier family for famousAleutian-feg-diring-bhis.manyyearseofudifficulifieldwork.Thanks is given to geology student interns Kirk E.Swanson (1980 and 1983),Mark J. Larsen (1981),David B.Edge (1982)for their field assistance,and to Brent Petrie,Bob Loeffler,and Irene Tomory of the Alaska Power Authority for their assistance with economic aspects and report preparation.In addition,YOGIilthanks is given to Donald R.Markle (presently with the Cooperative Extension eee Service of the University of Alaska JRoss G.Schaff (State Geologist of J Alaska),and Eric G.Sutcliffe (Representative in the Twelfth Legislature of the-ATaska State Legislature)for obtaining the research funds that were used to undertake this investigation. rr"S516/397 aaurs wish toan a sioe'neow madeae \a Black,R.F.,1976.Geology of Umnak Island eastern Aleutians as related to REFERENCES the Aleuts,Arctic and Alpine Research,v.8(1),p.7-35. Campbell,D.A.,and Economides,M.J.,1983.A summary of geothermal explora- tion and data from stratigraphic test well no.1,Makushin Volcano, Unalaska Island,Proceedings of the Ninth Workshop on Geothermal Reser- voir Engineering,SGP-TR-74,Stanford University,Stanford,Ca., 1,D.Rg Eee »Jd of cathe ==aExplorar6neerattgraphie'Test We :Makushin Volca- p.167-174. 1983),"A Summa Coats,R.R.,1950.Volcanic activity in the Aleutian arc,U.S.Geological Survey Bulletin 974-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. 516/397 Dames and Moore,1982.Aleutian regional airport,project documentation. Report for the City of Unalaska,p.44-45, Denig-Chakroff,D.N.,1985.Unalaska/Dutch Harbor_reconnaissance studyfindingsandrecommendations.Yorn Le he Alaska Power ()Authority,199 pp.A rewes,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.Geological Survey Bulletin 1028-S,p.583-676. ty,Stanford,Ca.<in press. <= 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 Univer- sity,Stanford,Ca.,t-presss PP:- 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, '§16/397 *, G.W.,1983b.Geothermal resource model for the Makushin geothermal area, Unalaska Island,Alaska,Geothermal Resource Council Transactions,v.7, p.99-102. serene et al (1983a),"Temperaturé Gradient Hole Results fromushinMakeothermalArea,Unataska Island,Alaska,"Geothermal Resources Council Transactions>>Ol.7,October 1983,pgs.95-98. Isselhardt,C.Es4 et al (1983b)"Geothe Resource Model for the Makushin Geothermal Area,Unalaska Island,Alaska,"Géoéhermal Resources CouncilTransactions,Vol.7,October 1983,pgs.99-102. James,Russell (1980),"A Choke-Meter for Geothermal Wells Which Measures Both Enthalpy and Flow,"Geothermal Energy,May 1980,pgs.27-30. 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(B5),p.4051-4072. Lankford,S.M.and Hill,J.M.,1979.Stratigraphy and depositional environ- ment 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. 516/397 Marlow,M.S.,Scholl,D.W.,Buffington,E.C.,and Alpha,T.R.,1973. Tectonic history of the central Aleutian arc,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 Symposium on the Development and Utilization of 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 in island arcs and active continental margins,American Journal of Science,v.274,p.321-355. Morrison-Knudson Company,Inc.,1981.Geothermal potential in the Aleutians: Unalaska.Report for the Alaska Division of Energy and Power Develop- ment,p.2-5. Motyka,R.d.,Moorman,M.A.,and Poreda,R.,1983.Progress report -Thermal _fluid investigations of the Makushin geotherma]area,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, 516/397 Or,Unalaska Island,Alaska:A model for fractionation in the Aleutian calc-alkaline suite,Contrib.Min.Pet.,v.73,p.69-87. Queen,L.D.,1984.Lithologic log and hydrothermal alteration of core from a"GOALEthe Makushin geothermal area,Unalaska Island,Alaska,Alaska Div.of Geol.&Geophys.Surveys Report of Investigations 84-23,8 pp.,1 plate. Reeder,J.W.,Denig-Chakroff,D.,and Economides,M.J.,1985.The geology\\\V6erouOr and geothermal resource of the Makushin volcano region of Unalaska Island,Alaska,Transactions of the 1985 International Symposium on ACDGeothermal Energy,Kailua Kona,Hawaii,in press.O Y Reeder,J.W.,1981.Vapor-dominated hydrothermal manifestations on Unalaska ,MegeeCapLYLfajblepelblation=Oewy Island,and their geologic and tectonic setting,1981 IAVCEI Symposium - \©Arc Volcanism,abstracts,sponsored by The Volcanological Society of Q Japan and International Associationof Volcanology and Chemistry of theQ:NN Earth's Interior,p.297-298.é YN'Reeder,J.W.,1982.Hydrothermal resources of Makushin Volcano region ofUnalaskaIsland,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.OK \ S Reeder,J.W.,1983.Preliminary dating of the caldera forming Holocene TyYSteTousttlvolcanic events for the eastern Aleutian Islands,The Geological Society -of America 1983 Annual Meeting,Abstracts with Programs,v.15(6), 516/397 .-_OK 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 o Zealand Bulletin,in press./ ;,CY g SS 2 Ty,' ;>.Reeder,J.W.,Economides,M.J.,And Markle,D/#.,1982.Economic and a <engineering considerationg for geothe yal development /in the Makughinwoca)Kh :4.Nolcano r gion of Unalaska Island,Alaska,Geothermal Resource Council wid Transactions,v.6,p.385-388.v OY é Reeder,J.W.,Edge,D.B.,and Swanson,K.E.,1985a.Complete Bouguer gravity S map of the Makushin Volcano and Dutch Harbor region of Unalaska Island,S Alaska,Alaska Div.of Geol.&Geophy.Surveys Report of Investigation,1>plate,in press.(\p SA Reeder,J.W.,Swanson,D.E.,and Larsen,M.J.,1985b.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.WY Reeder,J.W.,Swanson,K.E.,Larsen,M.J.,and Edge,D.B.,1985c.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. 516/397 Republic Geothermal,Inc.,1983.Unalaska geothermal project,phase IB final (unpublished)report.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 (unpublished)report.Report for the Alaska Power Authority,contract CC-08- 2334. a Republic Geothermal,Inc.,1984b.The Unalaska geothermal explorationYoeyproject,executive final (unpublished)report.Report for the Alaska "\ry Power Authority,contract CC-08-2334. ay) ©"Republic Geothermal,Inc.,1984c.The Unalaska geothermal exploration (}project:electrical power generation analysis,final (unpublished) report.Report for the Alaska Power Authority,contract CC-08-2334. Republic Geothermal,Inc.,1985.The Unalaska geothermal project,phase III ()final (unpublished)report for the Alaska Power Authority,contract\pvy -'\¢C-08-2334.s)NL eee _ys 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 Insti- tute,Hutchinson Ross Pub.Co.,Stroudsburg,Penn.,232 pp. "Vertical Steam-Water Flow in Wells with Heat Transfer,"Scientific 516/397 »% Software-Intercomp,February 1982. §16/397 Sa/ ,2"97.02utilyCEO i"Arce COMMENTS ON DRAFT CONTRACTGBETWEENTHEALASKAPOWERAUTHORITYmh(AND THE ALEUT CORPORATION .Ly rohan nymen INTRODUCTION A geothermal resource has been identified on Unalaska Island (the Unalaska Geothermal Project or Project)from which it may be economically feasible to generate 2 to ©megawatcs (or more)of electricity.The Alaska Fower Authority (Authority)is planning to study the feasibility of developing electric power generation at the geothermal site under the following arrange- meats: The Authority would construct,finance,and own (i)a geothermal power system and (ii)transmission facilities from the project site to a point ef interconnection with the City's distribution facilities.The Authority would secure the necessary rights-of-way for the transmission line and would agree to pay the Aleut Corporation (Aleut),the owner of the geothermal rights at the project site,royalty payments in consideration of the right to develop and use the peothermal resource. Any electricity generated at the Project would be sold to the City hy the Authority under terms that would fully reimburse the Authority for its cost of owning,operating,and maintaining the power system and related trans- mission facilities,including the portion of royalty payments paid to AleutwhichreasonablyrelatetotheproductionofProjectelectricity.L/Negoti- ation of any power sales contract between the Authority and the City would be contingent on the mutually favorable .conclusions of the Project feasibility -tudy.However,before proceeding with the study,the Authority desires that the City formally indicate its concurrence with the current Project concept --- in particular,the terms of the agreement between Aleut and the Authority. Though there are several provisions of this draft contract that would poten- tially affect the City,the contract terms establishing royalty payments to Aleut have direct monetary impact and are of major concern to the City. ROYALTY Sere CURRENT PROPOSAL»busbar Cos qirvee Factor 5panedrags Siendar §ReLREE,(2)th AE th VERT TB SR £electricity,and arolkaabhwhichwouldwaregecondinpe"POMawed "Wise based upon theYamuarofectricitygensratedintirquartétanchquartertheAuthoritywoaldadvancetoAleutspigiyeneoyadeseatoktBESDONS ine tl ye ¢ steene 2 Motential Problems tor the City In terms of overall!Project costs and relative economies,the rovalty payments as determined by the formula at Article C,-part 2 (b)(iii) woald probably not be a substantial expense.At an average production level of 2,280 kilowatts or less (5,000,000 kilowatt-hours per calendar quarter), the rovaltv payment determined by this formula would be approximately $0.0067 cer kilowatt-hour (i.e.,$.205 x 0.0325 =$0.0067).The royalty payment would vastitece about 8&2 of the total Project cost at $0.08 per kilowatt-hour. it ds prepused that Aleut will be given the option to develop,own,and operabe the Preject with the concurcence of the City. At average generation levels greater than 2,280 kilowatts,the rovalty rate would escalate from 0.0325 to a maximum of 0.063.Though this could increase Project cost to the City and the expense of the royalty pay- ments relative to other Project expense,the increase could partially be offset by a reduction in the City's Busbar cost that would theoretically accompany the increase in its system electric sales.As the City sold more power from th>Project,its fixed and overhead expenses would be spread over greater sales,thereby decreasing the average busbar cost. While this appears to be the intent of part 2.(b)(ii),AORagtpegotSPRYROASAREEItstatesthatBusbarcost"shall be thequbtfen'the sum of all costs directly attributable to generating electric power exclusive of the Project ...divided by the total number of kilowatt- hours that are or would be produced exclusive of the Project and supplied to the busbar."Determination of the sum of all direct costs is discussed below.The description of the denominator seems to imply that there is some choice as to what quantity of energy is used.Since a kilowatt-hour produced and delivered to the Busbar is the same,regardless of whether it is produced by the Project or the City's generators,the wording of the denominator description should be changed to "the sum of the kilowatt-hours that are pro- duced by the City and the Project and supplied to the Busbar."Besides more clearly stating the intent for the Busbar cost determination,this change would also avoid any needless concern as to the kilowatt-hours that would be produced absent the Project.All else being equal,the energy that would be produced by the City should be identical to that actually produced by the Project,but some might infer otherwise. Erernats het,The larger concern for the City is the _Provision for minimumrordypaymentsof$25,000 per calendar quarter.This minimum would effec- tively create a take-or-pay situation with regard to royalty payments at 1,790-1,950 average kilowatts.If the City's load fell below this minimun, the effective cost of che royalty payments would increase substantially.In- stead of a variable expense,the geothermal "fuel"could become an additional fixed cost.During the initial operation of the Project or in any period when economic conditions migit decrease the City's load below 2 megawatts,the min- imum royalty payment would increase the costs and risks to the City associated with the Vroject. The risk oft the minimum sayment is further compounded by there being a quarterly,rather than annual,determination.As such,the City could easily exceed $1°0,000 in royalty payments on an annual basis but still hesubject¢o additional payments in one or two quarters per year.An annual euarantee should provide Aleut with sufficient coverage of its cash flow re@uitenments,Basing the minimum royalty payment on calendar quarters seems Teo represent a needless risk te the City and potentially an unintended wind- ralblo tor Aleut. Definition of Busbar Costs The costs to be included in*the determination of Busbar costs in-clude all costs directly attributable to generating electric power and supply- ing it to the Busbar.Exhibit C to 'the draft contract sets forth expense categories from which relevant costs would be determined by the Authority and Aleut.-g PERS RIL Determination of exactly which costs are included in this calcula-A tion could have a significant impact on the City and therefore should be setforthindetailbythecontract.This is especially important since _preli-minary analyses have made estimates of the City's Busbar cost and couTa be construed by one or more parties as having some precedential value in later negotiations.If the contract defines the method for determining relevant costs,misunderstandings as to what was or was not agreed to in these earlier estimates should be minimized. The expense categories contained in Exhibit C are taken from ac- count references to standard electric utility chart of accounts,as typically used by larger utility systems.However,the City's accounts for its electric utility operation do not use this accounting system.Transferring the City's costs into the accounting system contained on Exhibit C would likely be a time-consuming,difficult process.It would be far easier and would better serve the intent of the agreement to?base the methodology for determiningrelevantCitycostsonitscurrentsygtemofaccounts.Though the accounts currently specified by Exhibit C may;be somewhat more detailed,administrativeandoverheadexpensesarenotenteredbyplantfunctionandwould,therefore,still require allocation to production,transmission,and other utility serv- ices.Keeping the City's own accounts as the basis for determining relevant costs would avoid any prelminary allocations or "judgment calls"to fit into the standard system of accounts. There are several methods commonly used for allocating joint admin- istrative and overhead costs for electric systems.No one claims to have the single correct method,as each method combines practicality with theory.A suggested method of allocating administrative and overhead expenses is shown on Table A for the City's accounting system. ROYALTY PAYMENTS -ALTERNATIVES In the current formula,royglty payment is not indexed to its func-tion or potential benefit to the citt.Instead,it is tied to the City'saveragecostofgeneration,exclusiveof the Project cost.In evaluating the Project feasibility,this may compound the number of assumptions involved in the analysis and add to the eventual financial risks faced by.the City in pur- chasing Project power.In these circumstances,the City must not only rely on estimates of its current power ulternatives but also must forecast its entire system cost through the term of a power sales contract.Instead of deciding Alternative A is better than Alternative B,given current construction and financing costs and future fuel expenses,a myriad of factors which could affect the City's total costs far into the future must be considered.This approach seems to be a burden on good planning practices. &£fA simpler,somewhat more stable approach would base the initialcoyalt,payment on some portion of estimated Project benefits which would beagreedtobytheAuthorityandtheCitypriortotheexecutionofapower sales agreement.In subsequent years,the royalty rate (which would be defined in units of $per kilowatt-hours produced and sold)would increase or decrease with a specified index or a weighted combination of several indices, such as labor wage rates,consumer price index,and fuel oil prices.Such a coyalty formula would reduce the imponderables in the feasibility analysis and avoid situations where Aleut could unfntentionally profit at the City's ex- pense.For example,an earthquake,tire,or a run of bad luck causes theCity's maintenance expenses to double!for the year.All else being equal, Aleut royalty payments would increase.as a result and further compound the City's fiscal problems.SenaomA formula for a royalty payment based on this concept might besimilartothefollowing: aRoyaltyPayment=kWh x RR x:(1) whe Tes FE kwh =Project energy delivered to City Point of Delivery;Ra&.RR =Royalty rate as determined in (2); t =Ratio of consumer price index for the preceding January 1,aspublishedbytheDepartmentofLabor,Bureau of Labor Statis- tics,to the consumer price index for the January 1 preceding the Commercial Operation Date of the Project. Royalty Rate =PV (n,r)x AF (n,1)x 25 (2) -AkWh where:oa PV =Present value of Project benefits to the City as determined by the Authority's feasibility study,exclusive of Project royalty payments;- AF =Annuity factor equalto (r/(1-(ltr)79); n =Term of power sales agreement for the Project; r=The City's estimated,effective annual interest rate for financing new investment.AkWh=Estimated average,afnual energy produced by the Project anddeliveredtoCityPoigtofDelivery. oe Allocation of {A and Overhead Expenses ministrative Operating Expense F for Allocation City Administration 7 Administrative &General Allocation Basis to Busbar Cost Central Services Parts Personnel Building Maintenance Change in Inventory weTTgeDebt Service Numerator or Denominator of Allocation Factor l/ i Items Included int Power Production -Other Line Repair &Maintenance Auto Repair &Maintenance Engineering Repair &Mainten Meter Reading Renewals/Replacements -Production Capital Equipment -Produc -OtHer -Other =Line Construction aS=part of factor numerator,° Factor (1) Factor (1) Factor (1) Factor (2) Factor (2) Factor (2) Factor (2) Factor Factor Sattareeion (1)(2) N,D N,D D D D D D D D N,D_N,D D D N,D D D factor denominator. FROM Ril BECK SEATTLE <CNXfy3aaiTmnQonNUvfr->2)REAST |lense WE Wea” R.W.BecKAND Associates,INC 3¥.07,ODL ENGINEERS AND CONSULTANTS #0.BOX bh18»BOR 2400 FOURTH &BLANCHARD BUILDING ° KA,ALASKA KETCPHULAN,ALASKA2121FOURTHAVENUE 0s 92901SEATTLE,WASHINGTON pata 206-441-7900 LENO.$S-1987-ER1-BX May 23,1986 Mr.David Denig-Chakroff Alaska Power Authority Post Office Box 190869 Anchorage,Alaska 99519-0869 Dear David: My suggestions for revising certain of the language for the Aleut APA contract are enclosed.The two areas in which revisions are suggested are(i)the definition of the City's Busbar costae and (ii)the Minimum Royalty. For the Minimum Royalty I have provided Options A and B.Option A simply calls for an annual "truing-up"whereby the Power Authority would bill Aleut for any overpayment of Royalty.This overpayment is defined as the amount by which the payments required by the current language exceed the greater of $100,000 or the Royalty as determined by formula in Section 2. Option B puts the Minimum Royalty as it really should be:a guaran- tee of minimum Royalty payments and not a method of advancing funds to Aleut.(Advance payments aré more appropriate as part of a security arrangement.) The main distinction with Option B is preventing overpayments from occurring during the year,so the City doesn't wait until after che end of the year for restoration of the overpayment.Rather than advancing money to Aleut,Option B assures that at the end of each quarter,Aleut will have collected at least $25,000,$50,000,$75,000,etc.This option would also benefit the City by smoothing cash flow.To compare Option B with the current draft's language,a table is attached which illustrates the two methods with some hypothetical figures. After further consideration,I still feel the concept of basing the City's Busbar cost on a hypothetical set of figures for investment and ex- penses which would otherwise have been incurred by the City will create more problems than it might solve.My suggestions on defining this concept in the contract are for the sake of clarity and should not be construed as an en- dorsement. FROM RL BECK SEATTLE 05'23/86 16:03 P.3 Mr.David Denig-Chakroff 2-May 23,1986 If you have any questions or comments on the suggested language, please let me know. Very truly yours, R.W.BECK AND ASSOCIATES,INC. Curtis K.Winterfeld Executive Engineer CKWicjt enclosures ec:Jeff Currier David Helsby FROM Rul BECK SEATTLE ve83/8G 14:45 Pe. «ft)BUSBAR COSTS DEFINED AS CITY'S HYPOTHETICAL COSTS 2.Royalties.(ad The Power Authority **#, (b)For Energy Resources *w #,Thea Power Share shall be the product of the total kilowatt-hours (kWh)produced and sold during the calendar quarter,multiplied by the appropriate Royalty Rate as set forth in (i)below,further multiptied by the City's estimated Busbar cost.Whenever used herein,***. Ci)The appropriate Royalty Rate #«##. Citi)The City's estimated Busbar cost for any give quarter shall be the quotient of (1)the sum of all costs directly attributable to generating electric power that would have been incurred by the City in producing or purchasing its total kWh requirements at the Busbar absent purchases from the Project divided by (2)its total kWh requirements at the Busber., Costs attributable to electric power generation for the purposes of this calculation shal!include all relevant costs under expense categories as set forth in Exhibit C Cattached hereto and made a part hereof by reference),The Power Authority and the City shall establish in consultation with Aleut the methodology by whloh the City's estimated Busbar coasts will be determined. FROM Rll BECK SEATTLE avS723/36 14:46 P. The agreed upon methodology shall include all necessary procedures and reasonable accounting controls and shall be required of the City as a convenant and condition of any power sales agreement. FROM RW BECK SEATTLE wu/23/85 14:46 P.4 IDEs a ANNUAL DETERMINATION OF MINIMUM ROYALTY OPTION A ome we ee ee ee ee eee ee ee oe te 0 OS PO OO Oe FO om a om oe mn ow 3.Payment of Royalty.(a)Upon ##©.Following recovery of any advance Minimum Royalty the Power Authority shall pay Aleut,on or before Januory 15,April 15,Juty 15,and October 15,the Royalty accured and payable for the pracading calendar quarter.On or before January 25 of each year,the Power Authority shall computa any overpayment of Royalty made to Aleut for the preceding calendar year and shall bill Aleut for said overpayment of Royalty,if any.The bill rendered by the Power Authority for such overpayment shall be due and payable upon receipt by Aleut.Tha amount of the overpayment,if any, shatl be datermined as the positive difference of, (i)the sum of all Royalty payments,including Minimum Royalty payments,paid by the Power Authority for operation in the preceding calendar year,less the greater of either, (iid)tha sum of all Minimum Royalty payments paid by the Power Authority for operation in the preceding calender year,or FROM RW BECK SEATTLE ws/23/86 14ia7 P.5 " Cilid the sum of the total Royalty to Aleut as determined in Section 2.above for operation in the preceding calendar year without consideration of any Minimum Royalty paid by the Power Authority. FRoOIt Rly BECK SEATTLE /23/486 14:48 P.6 " ANNUAL DETERMINATION OF MINIMUM ROYALTY OPTION B 2.Royalties.(a)The Power Authority *#*,The Royalty paid to Aleut shal!be determined as provided herein and shall be applicable te the maximum output of the [nitital production well or the equivalent output thereof;however,the Royalty paid to Aleut in any calendar year after commercial operation during the Primary Term and any extension term of the Lease shall not be tess than at the rate of One Hundred Ten Thousand Dollars ($110,000.00)per twelve (12)months.Royalty on Energy Resources ***, 3.Payment of Royalty.(a)Upon beginning commercial production and therafter during the Primary Term or any extension term of the Lease,the Power Authority shall pay quarterly Royalty which ts the greater of, (i)the Minimum Royalty multiptied by the fraction calculated as (1)the total days in the calendar year FROM RW BECK SEATTLE v3/23/86 14:43 P.7? ry through the end of the current quarter divided by (2) three hundred sixty-five (365)days,tess the total Royalty paid for the current calendar year through the end of the preceding quarter,or (iid the Royatty as determined by Section 2.for the current calendar year through the end of the current quarter less the total Royalty paid for the current calendar year through the end of the preceding quarter, (b)All payments of Royalty by the Power Authority to Aleut shall be due on January 15,April 15,July 15,and October {5 of each year. (ec)Concurrently with making each #+*, Cd)After the end of the Primary Term and each ten (10) years thereafter,the Minimum Royalty of $110,000.00 thereafter payable,as provided herein,shall be adjusted in the following manner.The adjusted Minimum Royalty to be paid after the Primacy Term,and each ten (10)year term thereafter,shall be the product of multiplying $110,000 by a fraction,the numerator of which w¥#«, COMPARISON OF METHODS FOR CALCULATING ALEUT ROYALTY PAYMENTS Royalty Calculated Per Section 2.31ILL039SADIMAWodd©OPTION B Royalty With Current Quarterly Oraft Centract Energy Per Sectian 3.Royalty Beginning End of Produced Busbar Royafty Payment Cumulative Quarterty Cumulative of Payment Payment Payment and Sold Royalty Cost for Para.Para.(Max of (i)Royalty Royalty Royalty Period Peried Due Oate €kth 3 Rate ('per kh)Quarter @ Go and {5122 Payment Payment Payment YEAR 13 Ol-Jan-90 9-331 -Mar-90 #.200 Cad $0 0 #5 Aa)$0 Ol-Apr-30 K-Jun-B 31-Sep-90 0.200 0 0 6 0 13,587 13,337 Ol-Jul-S0 30-Sep-90 15-Oct-90 1,838,500 0.0325 0.200 $10,000 13,699 10,000 13,699 13,699 2,0 38,587 C1-Cet-90 31-Dec-9390 35-Jan-91 7,058,800 0.0425 0.200 60,000 25,205 '56,301 3,1 70,000 35,000 73,307 YEAR 2: 15-Jan-3?$25,000 $25,000 Ol-Jar-91 31-Mar-91 1S-Apr-931 3,075,900 0.0325 0.200 420,00 $24,658 $26,000 $24,658 $24,658 B,onw 50,000 Of-Apr-90 XK Jur (S-Jul-S1 5,714,300 6.0350 0.200 40,000 24,932 B,H2 3,H2 &,000 40,000 90,000 Ol-5Sul-90 =X)-Sep-91 tS-Oct-S1 1,538,500 0.0325 0.200 10,000 14,76 10,000 14,75 74,73 2,000 115,000 01-Oct-90 31-Dec-SI 13-Jan-92 7,058,800 0.0425 0.20 60,000 3,206 $,205 35,208 139,000 3,000 150,000 ASSUPTIONS 3 Hinimum Royalty Gection 2.(a))equal$i00,OO . Coemerical operation begins August 12,1990 S3B/7E2e7GN-Pl"d6r& GEOTHERMAL PARAMETERS IN SIGNIFICANT SITES,WORLDWIDE, AND THEIR IMPLICATIONS ON THE UNALASKA DRILLING PROJECT PRESENTED TO THE ALASKA POWER AUTHORITY PATTI DEJONG,PROJECT MANAGER SUBMITTED BY J.A.ANSARI and M.J.ECONOMIDES UNIVERSITY OF ALASKA,FARTBANKS JANUARY 11,1981 6E.O7 ae INTRODUCTION Geothermal resources are found throughout the world.Some of the more ."Be :eo --oa,- 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. en a Ber WORLDWIDE GEOTHERMAL ENERGY Historically,commercial application of geothermal energy for generating wm ee Se ef ..a ek:ea electricity dates back to 1906 in Italy and for 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 ito 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 cost¢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. . ° ceencameeninmmemerneitdne naan marin te vince nitiosie-emaninaaaiiags Rican mn amcseerntcer lt seacar cae ie cam ia i |a: es i 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- ne Le menting 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 is 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. CERRO 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 f data.This model has been defined as a series of truncated and step-faulted 7 oe pyramidal 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. WALRAKEE (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 of 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.Fumarqles 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 r 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 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). , 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 lem 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 trend 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 nensicineasorencenihnrioeee eee rrentiey ses putram ainsi sgmoonasaansne anasapmmeeiaiin ammmbenaaese neers: ar "4 q on 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). De ee SITE MOST SIMILAR TQ 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. STATE 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). LA When exploitation began in 1951,the natural heat flow from the Field was 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 S° of 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. 10. 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 11. 1a 12 £ 16 s i =Blo}1a Fa zjae2galsa33©ot &%= a”&3 |=Bore |S at Fj 3 =' x °°s 6 arg ae ;; | (3)Distribution ar Costs 2--ak 2 Production Costs ou ok °if LRSSI 10 20 30 40 50 Transmission,km Figure 1 -Total cost of geothermal energy in relation to tne transmission distance.*thogsat\\\\ieetntar{ex.}yaa3IEak Gz mrsep)GSES)ee 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. Figure 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. CAsTELAvave "° LAROURELUO :boceme aqiane-Seanazzge GICCIOLETA "57 wv toee emecroc a (esatsane aFigure 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 andevaporiticintercalationswithinPaleozoicquartzitesandphyllites;(6)Triassicquartzitesandphyllites;(7)Triassic quartz pebble conglomerates;(8)porphyroidsandprophyricschists(Permian or Carboniferous);(9)Paleozoic quartzites andphyllites;(10)Paleozoic feldspatic quartzites and phyllites;(11)Paleozoicquartziticmicaschists;(12)the same as (11)but affected by contact metamorphism;(13)marble (Paleozoic or unknown age:in Niccioleta area metasomatic replaced by skarn). | oo Fy H Fy ras wereman portPAaviat*mas >PALLA INFERIO'POR WAS DAVEE WALPOSThaGUCGATIVail Simca ]iBecosttos Fives Velcon JMerino Grenites y Gonovorines TonetitasEC)E)edGE]."7 Commero ttetomortios IcqCusternerie sl Cratacice Poren sovce .Ss Figure 5 -Geologic Map of the Cerro Prieto Area AGAmCOS ALUVIALES SE CUCAPAM DE TMIGEN xnTeECaamiTICOYYMETASEOtmENTARORECIENT MOCAS RIODACITICAS fo}°o z ce o 3 <o z DEPOSITOS MO CCNSOLICADOS COMSTITUIOCS POM -oO c aARCILLAS,ARENAS ¥Y GRavAS;CON ESPESORES a &ve) DE 600 &2500 m a ”- .Ww sa -_- . a e eit tt 8 |SISCORDANCIA,CaneB 10 OF FACIES .0 CONTACTOFORMETAMORA ° a0 ------2 a Nfo] a <° 1S) LUTITAS DE COLOR CaFE CLARO CamalaNod °=.z &PROFUNDIDAD &COLORES GAtS CLARO Y GRS =-2OSCURO,INTERESTRATIFICADAS CON ARENISCAS i w DE COLOR GAIS CLARO,COMSTITUIOAS OE FRAG-<Lo Lal a MENTOS OE CUARZO Y FELCESPATOS CEMEN-oS YADOS IMDISTINTAMENTE CON CaARBONATOS Y e BS :fo)SILICE.SU ESPESOR ES DE 2000 m.arnoxm,oe -z og < 0 oO oO eae ROCAS IGNEAS Y METAMORFICAS CONSTITUI-oO:3'i . Hee tine /04S POR GRANITO,GRANODIORITAS,GNEISSES <q &Nesast=Ngee rt ¥ESQUISTOS.mw &2wsce2WwWeneoOowoaAue,= Figure 6 -Generalized Stratigraphic Column of the Cerro Prieto Area. corrrsrrr777 US.laa San DIESC son <= <oe €u.S. a \pee Mouama WEKICO ry beyPoeoNMp.7.V NENG : etetetelOioo| °EPICENTRO CF TEMES RES Lentee Sy Sg inessidecescoloceAlcnte: 4 ZOma GEOTERMICA "Ric LINEA DivISORtA i*). 50 :100 kmeel Figure 7 '-Regional Tectonic Map Lagunoe Satads {Katia de San Anardy io .te Sup erecan'Zectes ta Jopere- Fon oPE sete 8,o.4¢e BD vrcdn secentPrasetecere) £9 loere Deoterm-ces )Leones Plregetae 9 el]sO KM- ° DECALIFORNDA '7LOCALIZACION 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.SOceeRee Figure 9 -Basement Configuration eeea Sierra Cuwcapa Cerra Prieto \Mentcoul RioColorado @ mn{Toma courmisionaoad Meco Grenlittcee y Meresedimentaria Sedimentose ¢e Pledemonte (Abaontcos Aluviaies} .i . . roma Sedimentos DOettelces no Consotidedos (Ascit¥tos,Arenas y Grovos) Zone d6¢Leos Sedimenteos Consetidades Sumamente Frecturada Sedimentes DOettoteos Consclidades (tutitas,Limelites y Areniscas) Figure 10 -SW-NE Geologic Cross-Section PecomPrne 810%-{'remowecTRosPROFUNMDIDAD10 kas f / 4°/"a.7 0 ,j ;§kmN7&Kavo©&/c Aw /°cS4..."we./Q4éo>Tv ar f.©7 AS Q &/- a:ve /5 _,>xo)A es av Boundary of the geothermal field 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 Qm. Triangles indicate the locations of seismographs used in this survey: portable instruments are indicated by open triangles and permanent in- struments by solid triangles. | Pt.Kodin H-53°45" Moakushin Boy J Portoge Gay E |t 7 4 Km Sea 166°30'CLITTAS SSNS EE ping FARES sae. " of *Table Top-Unoloska NORTH.1 AED[]we ML S/"i wide Bay Cone Boy Map Symbols Fault:dashed where approximate Fumarole field Warm and/or hot springs Recent volcanic vent Caldera Unaltered volcanic rocks Plutonic rocks Unalaska Formation Figure 12 -Geothermal Site Locations ee .20 \-Map location (Northern part of Unalaska Istand) weeoneseePlatform below ;ar Field Steam.Vents.&-Sublimates J Springs:as yow Drainage GRO Seeps O Steam Vents se Dry(Old Spring'Location).© ED Snowficld,.August 1980a"He ,LOT 50 100 150 |200 <1 1 1 _"Yo Feet ,.>a7 10 20 30 40 60 Moters All Temperaturee in °C , -'All Flows"in liters/miduteAllConductivitiesin'pmhos/em.>69.7°89:Multiple. _Sources °Ss AoZ|---"Seeps _=ey1T7.3°_|2 ClieSiiitasResrve }25.4°To Glacier River %, .a :vi . Figure 13 -Detail at Glacier Valley Hot Springs on Unalaska Island. 800 ae TOTAL HEAT FLOW 760 600}a HEAT OOP . FLOW og KARAPITI THERMAL 300}= 200k )a 10h HOT WATERigEATFLOW ee 2, 1950 1960 197 1980 YEARS Figure 14 -Surface heat flow changes at Wairakei since 1950.The total heat flowhasbeensplitintotwocomponents:that from hot water flows (seeps and springs),and that from areal heat losses (thermal ground,pools) and specific steam flows.