HomeMy WebLinkAboutCity of Akutan Preliminary Technical Feasibility Report - March 2010 - REF Grant 2195475M
A. Kolker'. W. Curnrning2 , and P. Stellinil
AK Geothermal, LLC, Portland, OR
Cumming Geoscience, Santa Rosa, CA
3StelCo Magma Consulting, Bellingham, WA
iIntroduction ................................. ................... ................................................................................
'4
Project description and location ...................................................
.................. ............. .......... ...... �4
Context and Objective nfStudy ... ..............................................................................
........................ 4
Methodsand Scope ............................................ ................................................................................
5
Assumptions........................................................................................................
............................... 5
K.Geothermal Resource ..........................................................................................................
............... 6
Background............................ ................. ..........................................................................................
6
Geologyand Geochemistry ......................................................
..................................... —................ 6
OtherData—....................................................................................................................
___ ............ 14
ConceptualModels ............................................................................................................................
15
IV. Feasibility Assessment ................ ... .............................................
--........................................ 21
Issues Affecting Resource Existence and Capacity ..............................................................................
21
ResourceExistence and Size .................................................................................
......... .................. Z3
Confidence inResource Existence .................................................
—... ........ ................................... 23
Probable Resource Capacity .................. ......................................................................
..................... 23
Probability ofExploration Success ...................................
—..... ....................................................... Z4
Probability of Developmentfrom Accessible Area ...........................................................
....... .......... 24
Plausible Design for Power and Heat UdUzatkon--........................
................................................ 26
1 Power production ................... ............................................................
.................................. 36
I Direct use applications ........................................
.......................... —.................................. 27
3, Whole -system design ............................................................................................................
2Q
V.Conclusions and Next Steps .....................................................................................................
........ 29
VU. References and Bibliography ...........................................................................................................
B3
The geothermal system at Akutan Island has not been drilled, but exploration data indicate a
viable resource that could feasibly support planned development for power production and
direct use applications. The resource capacity, and the probability of exploration and
development success, are all dependent on the target. A shallow geothermal resource of 155-
180 'C (i.e., "outflow zone") is likely to be accessible for development at Akutan. A deeper,
hotter resource of >220 'C (i.e., "upflow zone") has a greater access risk but will be targeted
because of its potentially lower development cost. Two slim -hole exploratory wells are targeted
to verify the existence of these aquifers, and determine their potential for development. Two
follow-up wells would characterize the potential for an outflow zone that has greater resource
risk but a potentially larger access area.
Akutan Island is located 790 miles southwest of Anchorage and 30 miles east of Dutch Harbor.
As a volcanic island with accessible hot springs, it has been the subject of geothermal resource
studies since 1979. The City of Akutan (COA) is incorporated as a 2 nd class city, with a total
estimated population of 859 in 2007, including resident fishery workers of Trident Seafoods.
The COA encompasses 148 square miles, covering most of the island, including likely sites of the
proposed geothermal development. The City and Trident Seafoods are entirely dependent on
diesel fuel imported into the area for power and heat —with an average total demand of 4.3
1 - of power in the City of Akutan was $0.323 IkWh MW 1-7-8 MW peak). In 2008, the base cost
(Kolker and Mann, 2009).
The geothermal system on Akutan Island is considered one of the most promising hig
temperature sites in Alaska for geothermal resource development (Motyka et al,. 1993, Kolk
2007), but until recently only reconnaissance level exploration had been completed at the sit
The City of Akutan plans to develop its geothermal energy resource as part of a long -ter
comprehensive renewable energy strategy. In 2009, the City applied for and received ener
grant and loan funds totaling $3.7 million from the state of Alaska. Part of these funds was us
to conduct exploration activities in summer 2009 in order to better characterize the geotherm
resource and to target exploratory wells. The remainder of the funds will be used to suppo
exploratory well drilling in summer 2010.
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This report is a preliminary assessment of the technical feasibility of developing Akutan
geothermal resource. The discussion is preliminary in nature because it is based solely
surface exploration data, as no wells have been drilled on Akutan to date. A commercial proje
financing feasibility study is not possible until exploratory wells are drilled and tested in ord
I
to establish resource parameters such as temperature, well deliverability, fluid compositio
resource capacity, location and accessibty of the geothermal resource.
The objective of this study is to provide a preliminary technical discussion that will be combinel-,
with economic findings into a preliminary feasibility study of the type used to justify equi
investment for preliminary exploration drilling. Because of the relatively high cost ofoperatio
in remote areas of Alaska like Akutan, this study presumes that initial slim -hole wells would
drilled using a rig that could be helicopter supported. Such wells could establish t
temperature and fluid properties of the accessible resource before a road was constructed
that larger rigs could be mobilized to drill exploration wells capable of testing productivity. I
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This preliminary technical feasibility study draws primarily from three datasets in order
conceptualize the geothermal resource at Akutan and draw conclusions from that model. Tho
datasets are, in order of importance: 1) Previously recorded fluid chemical compositional da
(see Motyka and Nye, 1988); 2) Data from the 2009 MT survey (see Kolker et al., 2010); and
Soil gas chemical data (see Kolker et al., 2010). The fluid chemistry data is significant because
provides reservoir temperature estimates via chemical geothermometry and information abo
the likely conceptual geometry of the resource. The MT data indirectly "images" geolog
features associated with the geothermal reservoir. The soil gas chemical data constrains t
outflow geometry of the geothermal fluids. By means of these datasets, we are able to asse
the likely size, temperature, location, and geometry of the yet -undiscovered geotherm-
11
There are a variety of methods for estimating the production capacity of a geotherm
resource. Statistical methods such as "volumetric -heat -in -place" assessments are sometim
done at this stage when surface methods indicate that resource parameters suitable for
geothermal development are likely but no direct reservoir measurements are available fro
wells. However, such methods commonly lead to unrealistic expectations of capacity and
not lend themselves to an evaluation of the accessibility of that capacity, an issue likely to
significant at Akutan. To address this in a practical manner, this assessment compares a
contrasts Akutan to roughly analogous existing geothermal fields. This approach addresses n
only a plausible range of resource size but also the probability of exploration success a
development design in the context of access limitations.
The Akutan Geothermal Project was originally envisioned as a combined as and direct usit
project (Kolker and Mann, 2009) and, in this study, the phrase "geothermal development"
includes power production and direct use applications.
Based on the estimated cost of current electric energy production, the Geothermal Energy
Demand & Stakeholder Assessment (information Insights, 2010) found that a geothermal
project would be viable if it can produce energy for less than $0.21 per kWh. In addition to
current energy demand, there are planned and potential projects that will substantially
increase the energy demand load. These include a planned small boat harbor and airport, and a
potential, expansion of cold storage at the fish processor (information Insights, 2010).
The Akutan geothermal area ;is roadless. While exploratory drilling activities will be suppor
by helicopter, it is assumed that roads required for production well drilling and all subsequ
construction activities will be constructed. I
0
A state -funded aeothermal exploration program was carried out in Akutan Island in the early
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1980s (see Motyka and Nye, 1988). The program was limited to the immediate hot springs area
and included detailed geologic mapping, shallow (<150m) geophysical surveys, soil and fluid
geochernical studies, and hydrologic investigations. No drilling has yet occurred at Akutan.
In summer 2009, the COA executed a follow-on exploration program to better characterize the
geothermal resource on Akutan Island. The 2009 program included practical access
assessments, a geologic reconnaissance field study, soil and soil gas geochernical surveys
covering a broader area than the 1988 study, a remote sensing study using satellite data, a
review of existing hot springs geochernistry data, a magnetotelluric (MT) survey, and a
conceptual model analysis. A report on 2009 exploration activities was prepared for the COA by
Kolker et al. (2010), which presents the results of the exploration program and implications for
geothermal development. The next stage of exploration includes access analysis, fumarole
sampling and analysis, and the drilling of slim -hole (non -production) exploratory wells.
Akutan volcano is part of the Aleutian Volcanic Arc, which is Alaska's most promising setting
geothermal energy. Akutan volcano is one of the most active volcanoes in the Aleutians, wi
32 historic eruptions (Simkin and Siebert, 1994). An initial volcanic hazard review indicated th
the proposed geothermal development area was unlikely to be directly impacted by erupti
activity consistent with the previous 1500 years, excepting ash fall that might cause tempora
closure. Several thermal springs are located in Hot Springs Bay Valley, about 6 km from Akut
village (Fig. 1). Due to the frequent eruptions of Akutan volcano, there is likely to be a magmat
vent system and possibly an acid -core zone associated with gas rising from a persistent mag.
system (e.g. Reyes et al., 1993). However, the neutral cation geochemistry of the hot springs
strong evidence that a neutral system exists. Case -histories suggest that an acid -core zo
would isolate itself from a neighboring neutral geothermal system by a 'rind' of impermeab"
rock, typically created by silica and anhydrite deposition where incompatible acid and neutr"
fluids interact (Wood, 1994). Conduction through the impermeable rind or above episodic di
intrusions on the flank of Akutan volcano could provide heat for a neutral chloride geotherm
convection system adjacent to the active vent system. This is consistent with the rifting mod
of Lu et al., (2000) who conclude that Akutan's magmatic system is associated with island-wi
extension and related dike emplacement.
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166'4'9W 16610101`v 18615avw 16552VW 165*48'G-eV
Figure 1. Map of Akuton lslandshowing the geothermal area and pertinent geologic f eatures. Faults and rift zones
are identified from seismic data (J. Power, pers. comm.)
Five groups of hot springs with about ten vents have been identified, including tidewater
springs on Hot Springs Bay beach that are only exposed at low tide. Temperatures range from
54-94 'C. The hottest springs are HS8 and HS9 (groups A and B), with measured temperatures
of 94'C (Fig. 2).
N
Figure 2. Hot spring locations in Akuton's Hot Springs Bay Valley.
Most of the hot springs fluids are a dilute chloride to chloride -bicarbonate type (Fig. 3). T
unusually low dissolved solids concentration, relative to springs at the margins of many oth
geothermal systems, could indicate that they do not originate from a well-equilibrat
geothermal reservoir. For example, they might originate from partially equilibrated stea
heated surface water in a relatively small aquifer. Alternatively, a high flux of meteoric wat
might result in a reservoir water with to dissolved solids that is further diluted in ;.path
the surface springs by mixing with cold groundwater, The fact that Cl is the dominant anion
Akutan hot springs fluids indicates that the source of their hot water is likely to be
hydrothermal system since steam -heated groundwater is likely to contain more SO4 a
groundwater typically contains more HCO3 (Fig. 3). Although Cl is also a dominant anion in s
water, only the low elevation hot springs near the coast (in group E) have the relatively high
expected for such water. Therefore, the chemistry of the hot springs is likely to primarily refle
their geothermal origin, with some ambiguity regarding whether they come from a prima
upflow or from a partially equilibrated shallow reservoir heated by steam.
WII
LWX
SO4
Figure 3. Ternary plot showing relative concentrations of the anions chloride (0). sulfate (SO41, and bicarbonate
(HCO3). Fluids from groups D and E should be evaluated with caution due to likely seawater contamination.
Compositional data arefrom Motyka and Nye (19881'. Plothcs been generatedusing Powelland Cumming (2010).
Reservoir fluid temperatures can be indirectly estimated from chemical geothermometry. Th
is based on the principle that, when water is given enough time to reach equilibrium with th
rock it is saturating, the relative concentration of chemical species in the water will b
characteristic of the temperature at which it equilibrated, usually implying a significant mixe
volume of water. As some fluid in this equilibrated reservoir escapes and rises to a hot spri
through thermal buoyancy, it will usually be cooled by conduction and mixing faster than it w
chemically re -equilibrate. Because some chemical species, like silica, equilibrate faster tha
others, like sodium and potassium, the chemical composition of hot springs can be used
interpret the temperature and mixing history of a fluid in its path from the reservoir to t
surface. The most widely used liquid geothermometers involve silica concentration and relati
concentrations of the cations Na. K, Mg and Ca. Geothermometry calculations were applied
the 1988 chemical analyses of the Akutan hot springs using the Microsoft Excel liquid chemist
spreadsheets from Powell and Cumming (2010). Table I shows values for the common sili
(quartz) and cation (Na/K and Na/K/Ca/Mg) liquid geothermometers as applied to Akut
geothermal fluids.
Sample
Temp.'C
Quartz Cond.
Na K-Ca
a- -Ca Mg corr
Na/K (Fournier)
Akutan HS A3
94
1S9
189
169
20S
Akutan HS A2
84
iss
185
162
198
Akutan HS A3
nd
1 157
178
162
185
Akutan HS B!
47.4
1 139
179
138
211
Akutan HS C4
73.4
IS5
171
1 137
196
Table 1. Geothermometer calculations for Akutan hot springs waters from groups A-C. Groups D and E are omitted
due to likely seawater contamination. Compositional data are - from Motyka and Nye (1988) and the
geothermorneters have been generated using Powell and Cumming 12010), used on Giggenbach (1991) and
Fournier (1989).
9
The Na-K-Mg ternary plot in Fig. 4 shows the sodium -potassium (Na-K) geothermometer alon-
with the potassium -magnesium (K-Mg) geothermorneter (after Giggenbach, 1991) to highlig
reservoir processes and trends. This plot suggests that Akutan hot springs waters are poorly t
partially equilibrated and/or mixed. Samples B1 and A3 appear to be the closest to equilibriu
as expected given their location farthest up -valley, closer to the volcano flank. The trend amo
the samples in Figure 4 is toward an equilibrium cation temperature of 200 to 220 'C. Becau
the cations equilibrate more slowly than silica, higher geothermometry from cation than fro
silica concentrations is consistent with an interpretation of a geothermal reservoir where t
water equilibrated with the rocks at >210 'C farther than SOO m from the hot springs. While t
cation aeothermometry indicates that a geothermal reservoir of >210 'C probably exists
Akutan, the silica geothermometry of —160 'C indicates that the resource close to the hj.
springs that is easily accessible (<SOO to 1000 m distance and depth) is likely to be 160 to 1
T. This is consistent with the active silica sinter deposition at hot springs groups A-C, which
typically associated with nearby aquifer temperature close to 180
0
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Figure 4. Ter -nary plot showing relative concentrations of No, K, and Mg, and the Na-K and K-Mg geothermometers
(Giggenbach, 1986). Compositional data are from Motyka and Nye (1988) and the plot has been generated using
Powell and Cumming (2010).
The fumarole field located at an elevation of 3SO m on the flank of the volcano is likely to haA
Al -*TTa*=wtw-4faijtm!trole associated with the active voicanlp
vent. The flank fumarole occurs near the head of Hot Springs Bay valley about
southwest of the lower valley hot springs (Fig. 1). The fumarole field consists of a series of lo
to mode rately-p ressu red steam vents with temperatures of 99 'C, steaming ground, and boili
acid -sulfate springs covering an area of about 5,000 m' (Motyka and Nye, 1988). Akut
fumarole gasses have been sampled as part of the initial geothermal exploration study (Moty
and Nye, 1988), and again in 1996 in a USGS study (Symonds et aL, 2003). Unfortunately, bo
sets of data are not of sufficient quality to be used for reliable gas geothermometrV.
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The 2009 MT survey detects a resistivity pattern typical of most economically viable geotherm
reservoirs where a low resistivity, low permeability hydrothermal smectite clay cap "caps"
higher temperature, permeable geothermal reservoir, as illustrated by the resistivity map in Fi
5 and the cross-section CM1 in Fig. 6. Cross-section CMI has a bend in it to follow the
station coverage from the fumarole to the hot springs. It shows a relatively low resistivi
(green) layer that forms a cap over a higher resistivity (blue) zone. Unfortunately, because
difficult access by foot, MT stations were not located near the fumarole or in much of the ar
between the fumarole and the hot springs. Therefore, the pattern in this crucial area is large
inferred rather than directly imaged by the MT. With this caveat, the overall resistivity patte
can be interpreted in a geothermal context as illustrated by the more complete set of cros
sections and maps in WesternGeco (2009). The map of resistivity at -400 m elevation in Fig.
shows a tongue of high resistivity trending from the fumarole to the hot springs that
consistent with a path from a >220 'C upflow near the fumarole to a <180 'C outflow extendi
at least as far as the hot springs, as shown in the conceptual model in Fig 9.
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6001
001
5999
440 441 442 —3 444 445- 446
Akutan Geothermal Project
W.%w_.Gc& 3D KF224C
Reifivity at -400 fn elevation
Figure 5. Map of 3D MT resistivity at -400 m elevation with cross-section lines used to illustrate the conceptual
model (CM71) and the geometry of shallow aquifers in Hot Springs Bay Valley (hSV), The conductive clays in Hot
Springs Bay Valley are lower resistivity (green) than the more resistive (blue) area around the fumarole. The trend
between the fumarole and the springs is suggested rather than resolved by the widely spaced stations.
on
Besides the ambiguity related to the poor MT coverage of the ;interpreted upflow zone near t
fumarole, the most serious risk indication in the interpreted upflow and outflow path is the
ohm-rn resistivity of the clay cap. A hydrothermal clay cap is typically less than 10 ohm-m.
clay cap resistivity 20 ohm-m implies an unusually low intensity of clay alteration for a zo
overlying a geothermal reservoir, although this is sometimes observed in parts of geotherm
I
clay caps where an unusually high proportion of dense lava or intrusive rocks inhibit alterati
or where an earlier, much hotter episode of hydrothermal activity produced more resisti
shallow alteration more typical of the deep reservoir. I
140-0
I Wr�
Soo
600
4M
200-
a
-2CM
-1200
-14010
-1600
-WO
-XMIG
-22CO
-24CO
-260C
-2800
-30CIO
3 4 5
Distance (Km)
1400
1200
1000
801,
6.3c.
MOn
2M
0
-200
-400
-600
_qOIII
A000
Cm M, M
-1200
200
1 —400 15-0
law 70
50
40
10
-2200 201
2420 - -& w
............. 12
10
7
5
-3000
Akutan Geothermat Project
w..t.moo co 3o MT 22-Sep-2009 - Cunumn C-asdeme
Resistivity Crass -section Cat I
Figure 6. MT resistivity cross-section from a 3D inversion of the MT stations in a bent profile extending from the
fumorole to the springs in Hot Springs Bay Valley. The relatively low resistivity clay cap is green while the high
resistivity, high temperature zone will be in the blue shaded zone. The much lower resistivity clay cop (red) over the
very shallow aquifer that feeds the hot springs is red. A corresponding resource conceptual model is in Fig. 10.
Proposed locations of exploration wells are projected onto the plane of the cross section (numbered block lines).
The pattern of resistivity within Hot Springs Bay Valley suggests that at least one geotherm
aquifer exists in the valley and supplies the hot springs. According to Motyka and Nye (198
the Hot Springs Bay Valley is floored by a debris flow which is acting as an impermeable cl
12
over the subsurface hydrothermal system. From very shallow 1988 electrical resistivity an
seismic refraction surveys, they interpret this "cap" to be 30-40 rn thick. In the cross-sectio
shown in Fig. 7, the 2009 MT stations A016, A037 and A013 span the A and B hot springs th
have the highest geothermometry and measured temperature. The 1D MT inversions shown
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Fig. 7 for these stations have higher resolution at shallow depth than the 3D MT inversi
(Cumming and Mackie, 2010) and appear to resolve a relatively resistive zone at about -20 t
120 m, most likely corresponding to an aquifer with a temperature between 100 and 160
Although potentially productive, this very shallow aquifer is unlikely to sustain the high flo
rates required for long-term commercial generation of more than a MW.
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11 t 2, 31 4
Distance (Krn)
Figure Z Resistivity cross-section HSV showing a 1D inversion of MT data along Not Springs Bay Valley. A very thin
clay cop shallower than 50 m is 5 to 15 ohm-m resistivity, shaded orange to light green and yellow over an aquifer
in green at about 50 m depth. Another zone of high clay content extends to 350 m depth. Proposed locations of
exploration well locations are projected onto the profile line. Well #1 projects higher on the hill than its actual
location.
Near the hot springs, the MT also resolves a low resistivity clay zone below -120 m elevation
that extends down to about -350 rn elevation. This low resistivity is consistent with a clay cap
over a <180 'C outflow in a tabular aquifer below -350 rn elevation that locally upflows to a
shallower —100C aquifer at about -60 m elevation. The low resistivity zone at -120 to -350 m
elevation near the hot springs thickens near 'the shore at the end of the profile in Fig. 7 and to
the southeast side of the valley as shown in several cross -sections in WesternGeco (2009). The
geothermal manifestations are limited to the NW side of the Hot Springs Bay Valley, consistent
with the very low in resistivity and thin cap at that margin.
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Because the low resistivity clay extends from the hot springs across the valley and becom
thicker to the southeast, it is possible that the hot aquifer also extends across the Hot Sprin
Bay Valley, at greater depth to the southeast. However, hot springs do not appear where t,
clay is truncated against the resistive rocks on the southeast margin of the valley. The hi
resistivity rocks on the southeast cliff face host numerous unaltered or weakly altered dik
that seem likely to •' permeable. The high resistivity on the elevated southeast margin exten
from the surface to -300 m elevation in profile A-5 of WesternGeco (2009) and seems likely
promote cold clownflow that might penetrate the clay alteration into the deeper rock
c� . I - 1-11��♦ 1!
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The low resistivity alluvial fill in the vallev may act as an impermeable barrier at depth,
channeling an outflow from the area of the flumarole along the northwest margin of the valley.
In this model, the valley would not host a developable tabular reservoir. In a more •
model, compatible with the higher resistivity zone imaged below -350 m elevation in the valley,
the interpreted >160 'C outflow intersects the Hot Springs Bay Valley and extends into the
valley at -350 m elevation and leaks upwards to a —100 'C aquifer that supplies the hot springs.
The deeper >160 'C aquifer is a relatively accessible exploration target that might support
pumped production for a binary power plant.
Soil geochernical anomalies are clustered at three locations in Hot Springs Bay Valley. Arsen
(As), mercury (Hg), and carbon dioxide (CO2) all appear in anomalously high concentrations ne
the hot springs, which is not surprising. However, mercury (Hg), and carbon dioxide (CO2) a
also anomalously high at the junction of the Fumarole Valley and the Hot Springs Bay VaR
(Fig. 8). This indicates that Hg is likely being lost from a reservoir due to boiling and steam los
probably northwest of the junction. However, the location need not be close to the junction
the valleys since the Hg could be carried in alluvium from farther up Fumarole Valle
Nevertheless, the presence of the Hg anomaly is a favorable indication for targeting a w
northwest of the valley junction.
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Figure S. Map showing anomalous concentrations of CO2, Hg, and As in Akutan soils. All concentrations in ppm.
Black circles indicate proposed exploration well locations (see Fig. 12).
Two -• models were prepared to illustrate targets that could be reached from
accessible locations (Fig. 9). The conceptual elements common to these models include a
magmatic core and/or an acid -core of the volcano, a hydrologic barrier between magmatic/acid
core and neutral reservoir, a neutral chloride upflow at >220 'C, and a neutral chloride outflow.
Although all models have a neutral chloride upflow, its location, lateral size, vertical extent, and
temperature are • well determined • the available data and so it is assumed to be centered
under the fumarole. The heat source is conduction from the volcano or from deeper dikes
under the fumarole area causing convection. ♦ gas geochemistry has not been
successfully sampled at the fumarole, the extensive alteration zone and minor sulfur
sublimation suggests that it is likely • be associated with a >270 'C upflow, whereas the
modest rate of sulfur deposition suggests that the upf low is likely to be neutral chloride.
iv
Figure 9. Map view of water flow for conceptual model cross sections presented in Pgures -9 and iu. -,macing
reflects resistivity at -400 meters draped over the topographic map of the area. Yellow (model 1) and black
(model 2) arrows indicate the direction of shallow water outflow, respectively. Red circles indicate the location of
hot springs. The upflow region is near the start of the outflow arrows just east of the fumarole field.
The size of the outflow cannot be constrained due to data limitations associated with poor
access beyond the valley floor. However, the minimum size of outflow system appears to be
about -1000 x 500 m.
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ne,
K,
as TabWar aquffi�r
Silk_; 1000 20301 300X1
oowuwy
Figure 10. Conceptual Model 1 for the Akuton geothermal system. In this model, shallow outflow occurs in Hot
"arivas-Bav-valle-V confined bv stri ctural features and clay aquitards. An i mpermeable barrier (vertical gray line)
repeae y InJeCLEU WILn TTIUYTTIULIL UfKt:ZN UL UEf[JU11 1CL11U1gC SLLUI.N
walls. Red arrows indicate the flow of heated water, blue arrows indicate cold waterfloposed exploration
well locations ore projected onto the profile line, note that well #1 falsely projects on top of a hill. Well #1 will be
on the valleyfloor.
In Conceptual Model I (Fig. 10), the upflow is located near the fumarole and supports outflo
to and along the valley, Outflow occurs primarily as one or more tabular aquifers in t
subsurface. One aquifer appears to lie at a depth of <100 III and another at a depth of -SOO
beneath an aquitard of low resistivity impermeable clay. The outflow follows the surface tre,
of the valley, that is, initially flowing SE and then making an abrupt 90' turn to the NE. 11
In Conceptual Model 2 (Fig. 11), outflow does not follow any surface morphology but a
concealed subsurface structure or formation to flow ENE from the fumarole field towards the
NE margin of the valley. This case implies greater risk because the outflow is if accessible and
may not available for development.
loth of the interpreted outflow trends may be available to development. If both exist, they are
Rely to constitute a single interconnected aquifer. Many other conceptual model possibilities
,*xist but the most significant affect risk but not the choice of well targets.
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Active vokan-,
Smi- t I ually I'mundoy
fw tape Elfing tu" the 5��,Ice
dike-m P, rock
fw dovm fi-zNv
C7
4 Heat sotlra- at deoth
Q�Xk=, of dike') 0 SOO, I WO 20O 3 MW
Figure 11. Conceptual model 2 for the Akutan geothermal system. In this model, a very shallow tabular outflow
extends north of Hot Springs Bay Valley until water interacts with a concealed structural barrier and is forced to the
suifiace. As in model 1, an impermeable barrier (vertical gray line) exists between the acid core of the main volcano
and the geothermal resource. Heat source is likely a region repeatedly injected with magmatic dikes at depth;
recharge occurs through fractured rock exposed in the valley walls. Red arrows indicate the flow of heated water;
blue arrows indicate cold water flow. Proposed exploration well locations are projected onto the profile line, note
that well #1 falsely projects on top of a hill. Well #1 will be on the valley floor.
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The exploration data suggests that the likely upwelling location is in the general vicinity of the
fumarole field. However, the fumarole field is located on an extremely steep hillside at about
350 m elevation. This poses severe limitations in terms of access that would require very high
comparable to the *,roiect cost. Much of the rest of the Akutan
geothermal area has difficult access as well (Fig. 12). Hence, well locations and drilling targets
will have to be designed as a compromise between resource target risk and accessibility.
We propose to drill two to four slimholes at locations given in Fig. 12, the locations of which are
based on an analysis of access limitations and on the conceptual models of the Akutan
geothermal reservoir presented in Figs. 10 and 11. These wells will provide temperature
gradient measurements that will illustrate whether an accessible geothermal resource is likely
to exist at Akutan and will help design larger scale wells capable of production. The initial two
to four wells will be designed so that, if a permeable hot aquifer is encountered, it will usually
be possible to induce temporary flow so that fluid samples uncontaminated by drilling fluids
can be taken for geochemistry analyses. The focus of this will be analyses of the likely
temperature of the deep source of the thermal fluids, not representative production testing of
the resource. Production testing requires a much more expensive well design and a larger
drilling rig and, hence, road construction. Due to the roadless and rugged terrain on Akutan
geothermal area, drilling rigs for this exploration phase of the project will have to be mobilized
and largely supported by helicopter, limiting the economically feasible well design to small -
diameter ("slim -hole") wells.
The Well 1 target, located in Fumarole Valley -1200 m southeast of the fumarole will be drill-P-9
to a TVD of 1500 m (3500 ft.). This is a higher priority well as it appears to be the accessib
location closest to the high resistivity zone interpreted as a high temperature upflow zo
associated with the fumarole. One significant risk issue is its 1200 m distance from t
fumarole. Also, mercury anomalies tend to be highest on the periphery of a high mperatu t:a
zone, not over it. However, if this well encounters >250 'C and evidence of perm bility, t
likelihood of generating >20 MW with three production wells would be much higher thani
would be for 3 wells targeting the lower temperature outflow, Follow-up full-sized producti
wells could be drilled directionally toward the fumarole to the northwest.
Well 2, near hot springs group A, will be drilled to 500 m (1500 ft.). This well target has a high
probability of encountering a permeable reservoir than Well 1 but the reservoirs below Well
are likely to be lower temperature outflows. The site appears to be located where a 160 to 1
'C tabular outflow from the higher temperature upflow located to the southwest intersects H
'g e
h
s H
Springs Bay Valley. The geophysics suggests that two tabular aquifers could be penetrated
relatively shallow depths, although only the deeper aquifer would be expected to be capable
>1 MW sustained production, This well will be drilled in stages designed to make induced flo
from the aquifers feasible, in order to provide geochemistry constraints on the properties
the shallow and deep aquifers.
IN
Optional wells 3 and 4 will also be drilled to 500 rn (1S00 ft.). These wells, drilled at the
intersection of the Furnarole Valley and the Hot Springs Bay Valley, are targeted on the
projected outflow zone described in Conceptual Model 1. If one or both of these wells should
penetrate the outflow zone, it will likely be hotter than outflow fluids near Well 2 in Hot Springs
Bay Valley and they could prove a larger area accessible for targeting the tabular outflow.
Figure 12. Map showing accessibility in and around the Not Springs Boy geothermal area; and proposed locations
and depths of exploration wells. Any all-terroin vehicles (ATVs) will have to be transported to the field site by skiff
or helicopter. Green areas indicate easy walking and ATV driving, with light green areas indicating moderate ATV
driving conditions or regions in which ATVs would have to be dropped into place by helicopter. Helicopter landing is
excellent in green areas, moderate in swampy or inclined regions (in orange), and limited to specific sites in the
steepest terrain (red).
91
M= �
A preliminary feasibility study to support the exploration of a potential geothermal resource
like that at Akutan must necessarily accommodate significant uncertainty while establishing
the essential plausibility of the project. A more specific project feasibility study that
considers power plant and field design and operation will be conducted when the results of
the exploratory drilling and testing program are completed.
For the following reasons, the preliminary surveys indicate that there is a high probability that a
hydrothermal system exists at Akutan.
• The chemistry of the hot springs strongly suggests the existence of a neutral chloride
reservoir with economically interesting temperature. The fluid geothermometry tells a
consistent story, with the longer memory cation geothermometry detecting a >210 'C
reservoir temperature and the short memory silica geothermometry and presence of
sinter suggesting that 160 to 180 'C exists close to hot spring B. This pattern is typical of
volcanic geothermal systems.
• The flank fumarole field appears to have high heat flow and is surrounded by extensive
hydrothermal alteration. It is not depositing large quantities of sulfur and, therefore,
appears to reflect leakage from a geothermal reservoir rather than from a shallow
magmatic source or acid -core system.
• The MT resistivity pattern indicates that a hydrothermally altered clay cap exists near
the fumarole and probably overlies an outflow connection from the fumarole to the
highest temperature hot springs.
• Anomalous measurements of mercury and arsenic in soil are consistent with the
presented conceptual model and suggest that an upflow near the fumarole may extend
over 1000 m to the southeast.
• Supporting data sets including geological structure and rock types are -consistent wi
the existence of a permeable reservoir associated with structural extension.
• Although Akutan is an active volcano with frequent historical eruptions, the mo
attractive target areas near the thermal manifestations (fumaroles and hot springs) a
over 3 km from the active volcanic vent in a location where lava and significant a.
flows have probably not reached for >1500 years. I
While a hydrothermal system very likely exists at Akutan, the preliminary exploration progra
identified several risk issues as be particularly significant.
• The relatively dilute dissolved solid content of the hot spring water waters cou Ali,
indicate that they originate from steam -heated ground water that is only partial
equilibrated, which would most likely imply a relatively small reservoir.
• While the resistivity pattern is typical of a hydrothermal clay cap between the fumarol
and the hot springs, its 20 ohm-m resistivity is not as low as is typical of hydrotherml
IM
clay alteration over most permeable geothermal reservoirs. The 2 to 10 ohm-m
resistivity of the alluvium in Hot Springs Bay is more typical of hydrothermal alteration.
It is possible that, closer to the fumarole, alteration is more intense and resistivity is
more typical of a clay cap, but no MT stations image that area because of the difficult
im
more ambiguous between the fumarole and the hot springs. Because of the lack of high
resolution air or satellite images at Akutan, it is possible that undetected alteration
exists northwest of Hot Springs Bay Valley, between the fumarole and the hot springs.
Resource risk assessment approaches commonly divide the assessment into two parts; 1) a
assessment of confidence in the existence of a resource as a percent probability, and,
assuming the resource exists, an assessment of its size, usually as a statistical distribution (e.
Newenclorp and Schuyler, 2000). The probability of existence is sometimes restated as t
probability of exploration success; i.e., the probability that an exploration drilling progra
would discover at least one economically productive well. In many published geotherm
resource assessments, the assessment of existence is often not explicitly evaluated b
al
nominally included in the size distribution, for example, in the Western Governors' Associati
Clean and Diversified Energy Initiative Geothermal Task Force Report (2006). In the Weste
Governors' Association report, many geothermal prospects in the western USA with poor
I
indications of temperature over 220 T and much lower surface heat flow than Akutan a
assessed as having over 20 MW potential.
The most common method of estimating the probability of existence for a resource is to
arrange for a group of experts to review the available data and, based on analogous experience
with other geothermal prospect areas, estimate the confidence (as a probability) that the
necessary components of a resource exist together. For volcanic prospects that have hot
springs with cation geothermometry similar to Akutan's and an apparently non -magmatic
fumarole, few failure cases exist in which the most attractive target was drilled. The numerous
success cases differ in detail, particularly with respect to the geology and very dilute chemistry
characteristic of Akutan. For example, in the western USA, there are two developed geothermal
fields in volcanic systems with different geologic settings but broadly similar geochemistry, the
160 to 175 'C, —40 MW Casa Diablo field at Long Valley (Sorey et al., 1991) and the 160 to 180
'C, 45 MW Steamboat Springs Field near Reno (Mariner and Janik, 1995). In both of these
systems, it is entirely or mainly the lower temperature outflow that has been developed. At
Akutan, the combination of an apparently non -magmatic flank fumarole, a trend in cation
geothermometry to >210 'C, and silica geothermometry over 160 'C with sinter deposition
support the existence of a convecting geothermal resource on Akutan with a high confidence of
80%. The confidence that a >210 'C upflow or a >160 'C outflow exists and is accessible to
drilling is addressed in a separate section.
rhe capacity of the geothermal resource at Akutan in terms of electrical power can be
assessed using analogies, both the rough comparisons to the prospect estimates provided in
the Western Governors' Association report and the analogs to the 40 to 45 MW Casa Diablo
W
and Steamboat Springs developments. Because of the dilute outflow chemistry,
handicapping the Akutan likely 160 to 180 'C resource by 50% relative to these developed
reservoirs would be reasonable, giving an analogous low temperature resource capacity
estimate of 20 MW with an 80%, probability. Because a high temperature resource might
exist, a more optimistic capacity estimate for the entire system would be as high as 100 MW,
using the Western Governors' Association report assessments as analogs.
The initial drilling will provide more concrete resource parameters, including geothermal
fluid temperature, fluid and gas chemistry, rock properties and locations for follow-up
production test wells. The subsequent production wells would confirm fluid flow rate,
reservoir pressure, and fluid and gas composition. For a power plant design, the location of
geothermal production wells, site logistics, cooling temperature (air or cold water sink) and
similar issues would be specified.
Upflow Target
The probabty of exploration success in this case includes access constraints on exploration
well targeting. Upflow appears to occur directly beneath or slightly north/northeast of the
fumarole field beneath very steep terrain. The extent of the permeable zone, including in the
direction of location 1, is poorly constrained by the scant MT coverage. Because wells deviated
more than 1200 m may be required to intersect the permeable upflow, exploratory boreholes
will more likely penetrate the margin of the deep upflow. The margins are more likely to be hot
than permeable. Hence, although a well that actually extends past the fumaroles has a high
probability of achieving over 5 MWe equivalent productivity, perhaps 70%, the probability of
achieving this in two wells drilled from location 1 would be less than 35%. The probability of a
1500 m vertical hole at location 1 encountering economically significant permeability at >220'C
would be less than 15%.
Outflow Target
on the other hand, initially targeting the outflow system appears to be relatively
straightforward. The outflow occurs in low-lying valley topography, so access is not as difficult
as in the upflow zone. One significant concern is limited area for practical occupancy due to the
swampy nature of the valley floor, which could pose a problem for achieving an adequate well
spacing for development or for accessing the outflow if it is mainly located beneath the valley
floor. Despite these potential risks, the probability of a successful initial exploration well is high,
perhaps 80%.
A major risk for the Akutan geothermal project is accessibility. Typically, an initial explorati-M
well would be directed beneath a fumarole if the gas geochemistry suggested >270 and <330
temperature and neutral chemistry and the resistivity showed that such a well would test
conceptually attractive upflow. The likelihood of penetrating a high-enthaipy resource
24
Akutan is highest nearer the fumarole, even though the gas chemistry is not available to
confirm this. As noted above, although technically feasible, deviating a well laterally —1200 m
from location 1 to the fumarole would be expensive and prone to result in an incomplete
deviation. If, however, the initial vertical exploration slim -hole implies that the upflow zone
extends a significant distance to the southeast of the fumaroles, the directional drilling option
will be much more attractive.
Alternatively, the lower temperature outflow could be developed but this requires more wells.
These relatively shallow wells would not be drilled directionally and so they would be spread
out over a larger surface area. if a very permeable zone was encountered below 400 m depth,
2
like at the Casa Diablo field, the 20 MW might be produced from an area smaller than 1 kM
assuming pressure support from a larger area. Development in the outflow zone on the valley
floor is associated with some risks that are higher than is the case for the higher temperature
system targeted by Well 1. There may be a higher probability of cold water influx from shallow
or adjacent cooler aquifers. Due to the swampy nature of the valley floor, construction of the
greater number of well pads may limit much ofthe development to the ridge northwest of the
valley, requiring deeper wells and increasing well targeting risk by decreasing targeting
flexibility. These potential risks are tabulated in Table 3.
MODEL
MW
ADVANTAGES i
DISADVANTAGES
and Well
CAPACITY
RANGE
Upflow and
20-100
High-enthalpy
Lack of fumarole gas sampling increases risk of low
i Well I
permeability, high gas, or corrosive conditions
Single pad production for
Poorly imaged target geometry due to lack of MT
20 MW
coverage
Longer transmission lines I
Initial straight hole unlikely to directly test a small or
medium sized reservoir
Outflow
2-20
Better constrained by
180 'C requires more wells and 160 'C many more
and Wells
geochemistry
wells
Better constrained
2-4
resistivity geometry
Shallower cheaper wells
Shorter transmission lines
More reinjection wells required
Greater probability of injection breakthrough
Greater possibility of surface cold water influx
Swampy nature of valley could hinder exploration
.... .... ..
and construction activities
Table 3. Potential advantages and disadvantages associated wirn rne aeveicipment oi Me LWU MUJUF /-ir'ULU'l
geothermal resource models.
in some geothermal systems, particularly those with lower enthalpy, pressure in the system
maintained by ecting produced fluid back into the reservoir. This eventually causes resour
decline as temperatures are reduced. if managed appropriately, more than 30 years
operation should be feasible. Injection for a high temperature system is likely to require
N9
customized solution depending on the thermodynamic state of the system and the available
permeable zones for injection.
There are three major technologies commonly used to generate electricity from geothermal
resources. Which technology is appropriate for Akutan wilil be determined once the resource is
better constrained. The three types of plants are:
Dry steam: uses geothermal steam directly from a geothermal reservoir that has a fracture
system that is entirely steam. The reservoir steam temperature is typically 220 to 245* C. This is
the lowest cost system to develop but reservoirs that can support this development are rare. A
dry steam system is unlikely given the chloride hot springs.
ftqs�: geothermal steam is separated from hot water at the surface. The steam is delivered to
a steam turbine, while water phase is re -injected into the geothermal reservoir. The reservoir
fluid temperature is typically 200 to 330'C and so this might be feasible at the Well 1 location.
BinarV CVcIe: uses a secondary 'working' fluid (i.e., "binary" fluid) with a lower boiling
temperature than water, such as ammonia. Heat from the geothermal fluid causes the binary
fluid to flash to vapor via a heat exchanger, and the binary vapor is sent through the turbine t#,.
RRMM�•
Until recently, the minimum temperature for binary plants was -120'C. United Technologi-O
Corporation (UTC) developed a binary geothermal power plant currently operational at Che
Hot Springs which produces power from geothermal fluid at 80 'C, made feasible by the ve
low temperature fluids available for the cooling cycle. However, there are several proble
with the UTC system at Chena. The power plant has experienced multiple shutdowns sin
inception in 2006. Many of these have been explained by factors unrelated to the I geothermni
resource, such as an electrical fire in the plant building (Gwen Holdmann, pers. comm.
However, it is unknown whether some of the shutdowns are due at least in part to resour
issues. For these reasons, it may be too risky to use a UTC-type plant for power generation in
remote community such as Akutan.
*f these options, at Akutan, two are plausible designs for power production. Either a flash or -
binary plant might be feasible at the head of the valley, with production wells targeted towards
a high temperature upflow zone near the fumarole. Given the lower temperatures likely in Hot
Springs Bay Valley, a binary power plant is most likely. Beyond temperature, there are several
other reasons why a binary system may be a more attractive option for Akutan. The
construction time on site is shorter for binary plants because they are more modular and can be
R-1
't-arged to the island in large sections. Binary systems that use air-cooled condensers operate
more efficiently in cool climates and so that is not the handicap that it can be in other areas.
4-
Depending on the cooling system efficiency and design, the fooLprint of binary systems can be
imaller than that of flash plants, which would also be advantageous at Akutan.
A variety of sources including Lovekin et at. (2006) and the Western Governors' Associatiol
Clean and Diversified Energy Initiative Geothermal Task Force Report (2006), indicate that
reasonable average cost estimate for a new geothermal power development includi
exploration, drilling, facilities and power plant is about $3500/kWe. For new small-sco
geothermal power plants (<1 MW) in remote parts of Alaska, Kolker (2009) estimated avera
1
costs to be $7850/kWe. This estimate is too high for Akutanecause bthe likely larger pow
plant size would reduce capital costs due to economies of scale; however, it is useful 1
consider in the context of the remoteness of Akutan's location. At the stage of development
Akutan, before the resource properties are known, a reasonable assumption for the cost
development might be an average of the two estimates, at $5540/kWe.
Estimates for the corresponding levelized cost of power vary from $70 to $90/MWh depending
on assumptions used (e.g. Western Governors' Association Clean and Diversified Energy
Initiative Geothermal Task Force Report, 2006). Again, at Akutan some premium should be
added for the remoteness of the location.
The use of geothermal fluids for space heating is very important for Akutan, as it will furth"
reduce the diesel fuel consumption of village residents. Other applications include cold stora
for fish processing, greenhouse agriculture, resort development, the production of alternati
fuels for transportation, and others (see Information Insights, 2010). 1
in most geothermal fields that emphasize production of both heat and power, there arm -
dedicated well(s) for each application so that they can be independently managed based
their own demand. In any case, however, there will be at least a partial non -geothermal back -
system for heat and power. To provide a higher security of supply, a typical rule of thumb
that geothermal fields have at least one more production and injection well than are needed
any given time. There might be an option to provide a mixed system with one spare well th
would back up both the heat and power applications. I]
Whether a separate district heating system makes economic sense for Akuta n cannot
assessed before the location, temperature, and composition of the geothermal resource
known. Beyond fixed costs such as the well, heat exchanger, and other hardware, the cost of
district heating system is largely a function of two factors: (1) pumping and piping costs ov
the distance between resource and users (hence location of the production well needs to
constrained); and (2) the costs of processing to prevent scaling (hence, the temperature a
composition of the production fluids need to be constrained). I
Another possibility for development is a 'cascaded -use' approach. In a 'cascaded -use' scenario,
fluids from one production well would be used for multiple purposes. Fluids would first be
utilized onsite for power production. Spent fluids from the power plant would then be piped to
the village for direct use, and piped back to the 'reservoir' area for reinjection. This would likely
require fluids that are above -240 'C and have relatively low concentrations of total dissolved
solids (11 DS) to prevent scaling problems.
The difficulty with the cascaded -use approach is that the heat supply is complicated by a" t""
power plant issues as well as the heating issues; for example, a particular power piant scaie
corrosion mitigation option may be precluded by the need to service the heating syste
Therefore, combining the systems increases uncertainty for both. The geothermal heat supply
likely to be more secure if it utilizes a dedicated well for direct use applications, divorced fro
power production activities except for possible shared backup. While it is more expensive, t
economics might be attractive due to avoided fuel costs. On the other hand, the cascaded-ul
approach could work for Akutan, since the City already has a working heating system in plall
that could serve as a backup.
M
The feasibility of geothermal development at Akutan, and the type of development, is
dependent on the results of the exploratory drilling program. Exploration drilling will provide
necessary resource parameters that can now only be estimated from surface data.
Based on conceptual models built primarily from MT and geochernical datasets, it appears that
development of the Akutan geothermal resource for power and/or direct use may be feasible.
These datasets point to a shallow, tabular aquifer(s) of 1S5-180 'C (i.e., "outflow zone") and a
deeper, hotter resource of >220 'C (i.e., "upflow zone") that will be targeted because of the
potentially lower cost and lower land access required to develop >20 MWe. The initial
exploratory wells will attempt to verify the existence of these aquifers, and determine their
potential for development.
The probability of resource existence at Akutan is relatively high. The most likely range
geothermal reservoir conceptual models include a high-enthalpy upflow zone and a low
enthalpy outflow zone. Both these zones might be developable for geothermal heat and/
power. The resource capacity and the probability of exploration and development success a
dependent on the target.
Due to difficult access, the upflow targeted by Well 1 is poorly imaged and, for the same
reason, only the periphery of the likely upflow is accessible using a vertical test well. As a result,
the probability of encountering a resource using a vertical well at this location is lower than at
the outflow target, although fewer wells and much less fluid handling would be required to
develop a higher temperature system.
Well 2 on the outflow zone has a higher probability of encountering a productive resource,
albeit still constrained by access. However, more wells would be required to develop a 20 Mtie
capacity.
Because of the modest demand at Akutan, either the upflow or the outflow resource might be
adequate.
A few additional exploration activities should be conducted prior to or during the drilli
exploratory wells to reduce uncertainty in the well target expectations and improve t
-?.
modern geothermal industry oriented sampling and analytical methods; (2) Acquiring hig
resolution satellite imagery over the geothermal area; and (3) Further field tests to follow up
the • sensing results (see Kolker et al., 2010).
M
Cumming, W., 2009. Geothermal resource conceptual models using surface exploration data.
Proceedings, 34th Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford,
CA.
Cumming, W. and Mackie, R., 2010. Resistivity Imaging of Geothermal Resources Using 1D, 2D and 3D
MT Inversion and TDEM Static Shift Correction Illustrated by a Glass Mountain Case History.
Proceedings, World Geothermal Congress 2010.
Fournier R.O., 1981. Application of water geochernistry to geothermal exploration and reservoir
engineering. In: Geothermal Systems: PrimJplesand Case Histort Ryback and Muffler eds., John
Wiley and Sons, NY, 109-143
Fournier R.O., 1989. Lectures on geochernical interpretation of hydrothermal waters. UNU Geothermal
Training Programme, Reykjavik, Iceland. Report 10, 11989. www.unggtp.is/solofile/33667
Giggenbach, W., 1991. Chemical Techniques in Geothermal Exploration. In: The Application
Geochernistry in Geothermal eservoir Development F. D'Amore Ed. 1991 UNITAR/UN
Guidebook. I
R
Information Insights, 2010. Akutan Geothermal Energy Demand and Stakeholder Assessment.
Unpublished report to the City of Akutan and the Alaska Energy Authority, 34p.
Kolker, A., 2008. Geologic Setting of the Central Alaskan Hot Springs Belt: implications for Geotherm'
Resource Capacity and Sustainable Energy Production. Ph.D. Dissertation, University of Alas
Fairbanks, 203p. Available Online at: http://Www.uaf.edu/rap`/""students/``A"`"""lumnilKolker-dissertatio
2008.pdf I
Kolker, A., and R. Mann, 2009. Heating Up The Economy With Geothermal Energy: A M ulti-Com pone
Sustainable Development Project at Akutan, Alaska. Geothermal Resource Council Transactions, 331
Kolker, A., P. Stelling, B, Cumming, A. Prakash, and C. Kleinholt, 2010. Akutan Geothermal Project:
Report on 2009 Exploration Activities, Unpublished report to the City of Akutan and the Alaska
Energy Authority, 37.
Lovekin, J., Sanyal, S. and Sener, A., 2006. Potential Improvements to Existing Geothermal Facilities in
California. GRC Transactions, 30.
Lu, Z., C. Wicks, D. Dzurisin, W. Thatcher, and J. Power, 2000. Ground Deformation Associated with the
March 1996 Earthquake swarm at Akutan Volcano, Revealed by Satellite Radar Interferometry.
Journal of Geophysical Research, v. 105, No. B9, p. 21483-21495.
Mariner, R. and Janik, C., 1995. Geochemical data and conceptual model for the Steamboat Hills
Geothermal System, Washoe County, Nevada. Geothermal Resources Council Transactions, 19, 191-
200.
NA
Miller, T.P., G. McGimsey, D. Richter, J. Riehle, C. Nye, M. Yount, and J. Durnoulin, 1998. Catalog of the
historically active volcanoes of Alaska. USGS Open -file Report 99-582.
Motyka, R., and C. Nye, eds., 1988. A geological, geochernical, and geophysical survey of the geothermal
resources at Hot Springs Bay Valley, Akutan Island, Alaska. Alaska Division of Geological and
Geophysical Surveys (ADGGS), Report of Investigations 88-3.
Rl,S.Liss, C.Nye, and M.Moorman, 1993. Geothermal Resources ofthe Aleutian Arc. ADGGS
Professional Paper 114.
P. and Schuyler, l, 2800Decision Analysis for Petroleum Exploration, Second Edition.
Planning Press, pp. 618.
Powell, T., and W. Cumming., 2010. Spreadsheets for Water and Geothermal Gas Chemistry.
Proceedings of the Thirty -Fifth Workshop on Geothermal Reservoir Engineering, Stanford University,
Stanford, California, SGP-TR-188.
Reyes, A.G., Giggenbad, W.F., Sakeras lR, Sa|mnga N.D., VerQas, M,C, 1993. Petrology and
geochemistry of Alto peak, a vapor -cored hydrothermal system, Leyte Province, Philippines.
Gecthermnics,2l,479-SIg.
Richter, D.H., C.F. Waythomas, R.G. McGimsey, and P.L. Stelling, 1998. Geology of Akutan Island, Alaska.
USGS Open -File Report 98-135, 1 sheet, 1:63,360 scale
�imkin, T., and Siebert, L., 1994, Volcanoes of the World, 2nd edition: Geoscience Press in association
with the Smithsonian Institution Global VoIcanism Program, Tucson AZ, 368 p.
Sorey M.L, Suennnicht G��, Sturchio\ N.C., and Nordquist, G.A., 1991. New evidence on the
hydrothermal system in LumQ Valley ca|dera, California, from wells, fluid sampling, electrical
geophysics and age determinations ofhot spring deposits. Journal ofVolcanology and Geothermal
Resources, 48'pp. 229-264.
Symonds, R. B, R. Poreda,VKC. Evans, C.iJanU,and B. E. Ritchie, 2003. Mantle and crustal sources of
carbon, nitrogen, and noble gases inCascade-Range and Aleutian -Arc volcanic games. USGSOpen-
File Report O3-436.
WesternGeco, 2009. Magnetotelluric Survey at Hot Springs Bay Valley, Akutan, Alaska: Final Report — Q ra
Resistivity Inversion Modeling. Unpublished report prepared for the City of Akutan, Alask
Wood, C.P, 1994. Mineralogy at the magma-hydrothermal system interface inamesitevolcanoes, New
Zealand. Geology, 22, 7S-78.
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