Chena Geothermal Area

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GEOTHERMAL ENERGYGeothermal Home
Chena Geothermal Area




Area Overview



Geothermal Area Profile



Location: Fairbanks, Alaska

Exploration Region: Alaska Geothermal Region

GEA Development Phase: Operational"Operational" is not in the list of possible values (Phase I - Resource Procurement and Identification, Phase II - Resource Exploration and Confirmation, Phase III - Permitting and Initial Development, Phase IV - Resource Production and Power Plant Construction) for this property.

Coordinates: 65.0525°, -146.0558°


Resource Estimate

Mean Reservoir Temp: 98°C371.15 K
208.4 °F
668.07 °R
[1]

Estimated Reservoir Volume: 2.74 km³2,740,000,000 m³
0.657 mi³
96,762,186,815.54 ft³
3,583,784,696.06 yd³
2,740,000,000,000 L

Mean Capacity: 0.4 MW400 kW
400,000 W
400,000,000 mW
4.0e-4 GW
4.0e-7 TW
[2]

USGS Mean Reservoir Temp: 95°C368.15 K
203 °F
662.67 °R
[3]

USGS Estimated Reservoir Volume: 1 km³ [3]

USGS Mean Capacity: 2.75 MW [3]

Figure 1. Chena Geothermal Area Location Map.
Figure 2. USGS image of Chena Hot Springs, 1917.[4]

The Chena Geothermal Area is a component of the Central Alaska Hot Springs Belt (CAHSB), an expansive low temperature geothermal system containing approximately 30 known hot springs trending east-west in central Alaska.[5] The Chena Hot Springs, located 60 miles to the northeast of Fairbanks, are the surface expression which initially indicated the presence of a geothermal system.

The earliest documented discovery of the hot springs by a mineral surveying crew occurred in 1904. Robert Swan, a man suffering rheumatic disorder, learned of the existence of the springs and in 1905 initiated commercial development; by 1911 the hot springs resort had expanded to include a bathhouse, twelve cabins for visitors, and a stable.[6]

Chena Hot Springs was a popular destination for sleighing parties from Fairbanks during the winters in the early 1900s, with two roadhouse stops along the route. However, during the summer the direct route from Fairbanks became very swampy and impassable on horseback; longer yet more accessible routes via Fairbanks Creek and Olympia Creek were used during these months (see Figure 3).[4]

Figure 3. Location of Chena Hot Springs in Fairbanks district, AK.[4]

The Chena Hot Springs Resort has continued its operations and is the premier hot springs resort in Alaska. The Chena Geothermal Area has two very unique qualities: 1) it is the first geothermal power plant in Alaska, installed in 2006, and 2) the geothermal power plant utilizes a lower temperature geothermal fluid than any other geothermal power plant in the world.[7]

Figure 4.Chena Hot Springs oblique air photo, looking to the southwest.[8]




History and Infrastructure



Operating Power Plants: 1


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Developing Power Projects: 0

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Power Production Profile

Gross Production Capacity:

Net Production Capacity:

Owners  :
  • Chena Hot Springs

Power Purchasers :

Other Uses:


Figure 5. Aurora Ice Museum with protective covering at Chena Hot Springs Resort.[6]

Chena Hot Springs Resort has one indoor pool and an outdoor rock lake that are both supplied with 94-110°F geothermal waters. The resort offers conference facilities, an activities center, lodging, dining, and a spa, among other facilities. Approximately 20 geothermal wells on the property support Chena Hot Springs Resort’s heating to the buildings, the Aurora Ice Museum, a geothermal greenhouse, and the geothermal power plant.[6]

One of the more unique aspects of the resort is the Aurora Ice Museum (Figure 5). The museum was built to increase tourism to the area and also offers year-round employment for local ice artists. Its structure consists of ice blocks cut from a local beaver pond during the winter, and is maintained using a 15 ton (53 kW) absorption chiller designed by Energy Concepts Co., which utilizes geothermal fluids.[6] Forbes magazine voted the Aurora Ice Museum the dumbest business idea in 2004 (it had melted that year). However, with the assistance of the geothermal fluids, this facility operates year-round, costs $12/day to operate, and attracts 10,000 visitors annually.[7]

The geothermal greenhouses, with an area of 400 m2, allow the resort to grow fresh produce such as tomatoes, lettuce, and raspberries for use in their restaurant (Figure 6). The district heating system at Chena Hot Springs Resort saves $300,000 annually in heating fuel and enables the feasibility of projects such as the geothermal greenhouse.[6][7]

Figure 6. Geothermal greenhouses at Chena Hot Springs Resort.[6]

In July 2006, the first of three 200 kW United Technologies Corporation (UTC) Organic Rankine Cycle (ORC) power generating modules was installed and began operation on August 20, 2006. The second ORC power plant module was installed in November/December and brought online on December 16, 2006 (shown in Figure 7).[9] A third ORC unit was brought online in 2009.[10]

Figure 7. Chena Geothermal Area ORC Units 1 and 2.[9]
Chena Area Timeline

1904: Mineral surveying crews discover hot springs in the Chena Area.[6]

1905: Commercial develop of a resort is begun under Robert Swan.[6]

1917: U.S. Department of Agriculture samples hot spring waters in the Chena Area.[4]

2004: The DOE Geothermal Technologies Program proposes to test a PureCycle 200® Organic Rankine Cycle generator at Chena Hot Springs Resort for geothermal power production.[11]

2005-2007: DOE funds a comprehensive 18-month resource assessment of the geothermal potential of the Chena Geothermal Area.[11][12]

2006: Installation of two 200 kW United Technologies Corporation Organic Rankine Cycle power generators is completed at Chena.[7][9]

2007-2010: Production well temperatures steadily decline from 165° to 159°F. Well TG-12 is drilled to greater depths, encountering a hotter resource with improved fluid flow.[10]

2009: A third Organic Rankine Cycle generator is installed at Chena.[10]


Regulatory and Environmental Issues


The UTC ORC modules were designed to utilize the cold water resources at Chena to water-cool the power plant modules. The water supply is drawn from a shallow well, and once the water runs through the condenser, it is discharged into Monument Creek. The cold water temperature increases by 10°F after it has run through the condenser. In order to discharge the water to Monument Creek, a water use permit was obtained from the Alaska Department of Natural Resources and a discharge permit (2006DB0040) was required from the Alaska Department of Environmental Conservation. An emergency shutdown procedure is in place to prevent the working fluid (R134a refrigerant) from discharging into Monument Creek in the case of a leak.[11]

Future Plans


Chena Hot Springs Resort intends to expand geothermal power generation by up to 500% in the coming years. The proposed future work is aimed to characterize the deep geothermal system, including an examination of the heat transfer mechanism, recharge rates of heat and water, and fluid pathways of the Chena geothermal system. A deep (greater than 1,000 m) well was planned during 2007, but was subsequently canceled due to U.S. Department of Energy (DOE) funding constraints.[13] A deeper slimhole drilling program was proposed and strongly recommended for Geothermal Resource Evaluation and Definition (GRED) III Phase II.[8]

GRED III Phase II was carried out with additional deep drilling to approximately 2,700 ft, but the anticipated temperature of 200°F was not encountered. [14] However, since the Chena Geothermal Area is representative of many other geothermal systems located within the Central Alaskan Hot Springs Belt (CAHSB), its development may serve as a model to promote the utilization of geothermal resources in Alaska. [8]

Exploration History



First Discovery Well

Completion Date:

Well Name: Well #7

Location: 46.9218796°, 7.1659449°

Depth: 713 ft217.322 m
0.217 km
0.135 mi
237.666 yd
[11]

Initial Flow Rate: 13.88 kg/s832.8 kg/min
49,968 kg/hour
1,199,232 kg/day
13.88 L/s
220.002 gal/min
[11]

Flow Test Comment: Flow test enabled estimation of drawdown of 148 ft in the production well at the required production rate of 1000 gpm for power plant operation. [11]

Initial Temperature:


The Chena Hot Springs waters were initially sampled by the U.S. Department of Agriculture in 1917. The following observations constitute the earliest scientific research at the Chena Geothermal Area. The geochemical analysis indicated sodium carbonate-type waters, consistent in the two springs measured. Low calcium and magnesium concentrations were recorded, however, with elevated levels of silica and sulfate. Surface fumaroles were tested with a flame to indicate carbon dioxide concentration. Sulphur deposits and algal growth were present in the vicinity of the hot springs. The springs’ overall flow rate was measured at 220 gallons/minute, and a warm seepage was present 200 yards to the southeast of the uppermost spring. The geological formation in the vicinity of the springs was primarily granitic, with schist present on the higher slopes; the granite appeared to be intrusive into the schist. Also, the temperatures of the two springs were measured at 149°F and 124°F, respectively.[4]

From 1973 to 1974, Norma Biggar completed a Master’s thesis project regarding the Chena Geothermal Area under the supervision of Dr. R. B. Forbes at the Geophysical Institute of the University of Alaska Fairbanks (UAF). This study marked the Geophysical Institute’s first research project in geothermal resource assessment.[15] Biggar’s thesis work included field geological mapping, rock sampling of plutonic and metamorphic rocks for petrographic and age determination studies, a ground temperature survey with a 0.5 m probe, geothermometry calculations from existing geochemical measurements, and a geomagnetic survey.[5] The granitic pluton was determined to be 59 Ma based on biotite from a monzogranite rock sample. The ground temperature survey produced an elongated southeast-trending anomaly with a maximum recorded temperature of 48°C. This thermal anomaly was inferred to run coincident with faulting in the granitic pluton, indicating the potential presence of fault-dominated geothermal fluid flow. Biggar hypothesized the inferred faulting was the source for Chena Hot Springs.[15]

Continued studies at the UAF Geophysical Institute from 1979 - 1980 further developed the understanding of the Chena Geothermal Area, building upon Biggar’s thesis work. Additional exploration activities performed included: aerial photography analysis, geological mapping to delineate contacts and faulting, helium soil gas sampling, mercury soil sampling, a shallow electromagnetic profiling survey using the EM-31, Schlumberger resistivity soundings, and a seismic refraction survey.[15] The results of these investigations were largely consistent with Biggar’s hypothesis. The surface expression of the southeast-trending fault was directly mapped in the field in 1980 and confirmed through aerial photography analysis, shallow electromagnetics, and anomalous helium concentrations which were measured along the suspected fault.[15] The helium anomaly was posited as an attractive shallow drilling target for subsequent studies, but was later determined to have sparse sampling coverage with the anomaly positioned at a weak thermal manifestation.[16] The Schlumberger resistivity and seismic refraction surveys revealed fractured, water-saturated quartz monzonite bedrock to at least 40 m depth under the alluvial fill. These data contributed to the overall conceptual model of Chena Geothermal Area at the time; the hypothesis entailed the development of hot springs due to fracture-dominated geothermal fluid flow at the margin of the Chena granitic pluton.[15] However, the studies from 1979 - 1980 concluded that the Chena geothermal resource was not adequate for power generation purposes with the available technology.[5] Limited exploration activities occurred during the following years with the exception of a few shallow wells (less than 100 m depth) drilled in the vicinity of the hot springs between 1998 and 2005 by Chena Hot Springs Resort.[5]

A DOE-funded research project of the Chena Geothermal Area was performed from 2005 - 2007. This study, the GRED III Phase I Project, was conducted over an 18-month duration as a comprehensive geothermal resource assessment. The initial aim of the project was to determine if the Chena Geothermal Area was capable of supporting a 10 MW geothermal power plant in order to justify the expense of a transmission line to Fairbanks, a 33 mile distance.[11] This exploration program involved geophysical, geological, hydrological, and geochemical studies alongside a temperature-gradient hole drilling program executed to better constrain the Chena geothermal system’s resource potential. Nine multidisciplinary tasks were organized by separate principal investigators (P.I.s) and consisted of the following exploration activities, as outlined in the GRED III Phase I Final Report:(Holdmann, Benoit, and Blackwell 2013)

  1. Installation of a system of GPS benchmarks and a near-surface radiometric survey; P.I. Paul Metz, UAF.
  2. Delineation of conductivity vectors in order to characterize the interaction between the deep and shallow reservoirs; P.I. Dick Benoit, Sustainable Solutions.
  3. Airborne magnetics and radiometrics; Survey conducted by Fugro Airborne Surveys, Inc.
  4. Detailed geological mapping utilizing aerial and land-based surveys, as well an assessment of structural features based on remote sensing imagery; P.I.: Jessica Larsen and Amanda Kolker, UAF.
  5. FLIR (Forward Looking Infrared Radiometer) survey performed to compile a high-resolution surface temperature map; P.I.: Jonathan Dehn, UAF.
  6. Audio-magnetotelluric (AMT) and controlled-source AMT surveys to assist in the identification of upflow zones and drilling targets; Survey conducted by Zonge Engineering, Inc.
  7. Shallow temperature-gradient hole survey to improve the understanding of the Monument Creek Valley thermal regime; P.I.: David Blackwell, Southern Methodist University (SMU).
  8. Geochemical and isotopic analysis of geothermal and cold wells in the Chena Geothermal Area, in addition to a hydrological study to determine the natural recharge rate; P.I.: Kenji Yoshikawa, UAF.
  9. Passive micro seismic survey deployed in November 2006, the results of which are not yet available for the GRED III Phase I Final Report.

The comprehensive resource assessment in the GRED III Phase I Project was performed concurrently with the installation of a small, 200 kW geothermal UTC power plant module in August of 2006.[12] The Chena Geothermal Area was determined to be capable of supporting 1 - 5 MW of geothermal electricity production.[11] The results of this exploration program have furthered the conceptual understanding of the Chena Geothermal Area; these insights from GRED III Phase I are described in the Geology Narratives.

The resource characterization project at Chena Hot Springs continued with Phase II of the GRED III Project. The intent of GRED III Phase II was to achieve enhanced improvement over the conceptual model of the deep reservoir to enable power production to be scaled up at Chena Hot Springs, with a potential target of providing electricity to Eielson Air Force base at a distance of 40 miles away. The duration of Phase II of the exploration program was May 2009 - March 2010. A deeper well, TG-12, was being drilled to approximately 2,500 - 3,000 ft depth, but the hypothesized temperature of 200°F was not encountered; rather, a temperature reversal was measured, and the drilling ceased at 2,700 ft.[10] The average measured temperature in the well was 176°F. Further drilling was planned for later in the year, from May - September 2010, as well as updating the reservoir model and plugging non-producing holes with bentonite.[14]


Well Field Description



Well Field Information

Development Area:


Number of Production Wells: 2; Well #7, Well TG-8 [10]

Number of Injection Wells: 1 [11]

Number of Replacement Wells:


Average Temperature of Geofluid: 74°C347.15 K
165.2 °F
624.87 °R
[12]

Sanyal Classification (Wellhead): Extremely Low Temperature


Reservoir Temp (Geothermometry): 110°C383.15 K
230 °F
689.67 °R

Reservoir Temp (Measured):

Sanyal Classification (Reservoir): Very Low Temperature


Depth to Top of Reservoir: 230m0.23 km
0.143 mi
754.593 ft
251.53 yd
[2]

Depth to Bottom of Reservoir: 915m0.915 km
0.569 mi
3,001.969 ft
1,000.653 yd
[2]

Average Depth to Reservoir: 573m0.573 km
0.356 mi
1,879.921 ft
626.639 yd


Figure 8. Wellfield layout and temperature contours at 0.5 m.[8]

The first production well for the ORC power plant module was Well #6, located adjacent to the hot springs and drilled to a depth of 130 ft (see Figure 8). This well was replaced by a new production well, Well #7, once an improved conceptual understanding of the shallow system was achieved during the GRED III Phase I exploration program. This new production well was drilled to 713 ft. The pipeline transporting the geothermal fluid is an 8-inch-diameter insulated HDPR pipe which is 3,000 ft in length. The heat loss between the production well and the power plant is 1.8°F. After some experimentation, TG #7 was selected as the main injection well. TG #7 demonstrated a high injectivity index and was drilled to a depth of 702 ft.[11]



Research and Development Activities


At the recommendation of the DOE Geothermal Technologies Program, UTC approached Chena Hot Springs Resort in 2004 with the idea of testing its PureCycle 200 modular ORC power generation system at Chena Hot Springs. The PureCycle 200 module had previously been applied towards the utilization of waste heat from industrial processes, and UTC’s new objective was the cost reduction of geothermal power generation equipment from $3,000/kWhr installed to $1,300/kWh installed. Specifically, UTC’s objective at Chena was the demonstration of the feasibility of electricity production from a 165°F geothermal resource with 98% availability at a cost of less than $0.05/kWh.[11]

UTC engineered its PureCycle 200 module design to cater to geothermal applications. Some modifications included changing the working fluid to R134a refrigerant to allow the use of less expensive, commercially available components; developing low cost heat exchangers; modifying the turbine design; and adapting the heat exchanger design. Generally, a low-temperature resource such as the Chena Geothermal Area, with wells producing fluids at 74°C (165°F), is not a suitable candidate for an ORC power plant because the temperature is too low. However, due to the availability of cold (3°C, 37°F) river water year-round, an ORC cycle is possible with a thermal efficiency of 8%.[17] The first UTC ORC module was designed to be water-cooled in order to take advantage of this cold water resource at Chena. The water supply system was engineered to require no pumping, reducing the parasitic load of the system. The second ORC module can be cooled with air or water.[11]

As of 2009, the Chena power plant is the lowest temperature geothermal resource utilized for electricity production in the world.[18] The project has received international recognition, including: the Project of the Year Award from Power Engineering Magazine; the Green Power Leadership Award from DOE and the Environmental Protection Agency; and the R&D 100 Award from DOE.[9]

A collaboration was established in 2009 between Chena Power, UTC, Pratt & Whitney Power Systems, and Quantum Resources Management. Their objective is to apply the PureCycle modules to a mobile power generation platform for coproduction of electricity from oil and gas wells using similar technology as applied at the Chena Geothermal Area.[18] This technology has been applied at the Peppermill Resort and Casino in Reno, NV. Also, a mobile power plant is generating 220 kW in Utah utilizing 600 gpm of 210°F water.[18]


Technical Problems and Solutions


When the power plant was originally built, the operators experienced problems with the cold water supply during the late winter and early spring due to cold ambient temperatures (dropping to -50°F) and a lower water table. ORC Unit #1 was temporarily shut down due to these issues. The installation of a second air-cooled condenser and the construction of a cooling pond were the recommended solutions to pursue in 2007.[9] As of 2007, during the summer months, the ORC modules are water-cooled from a gravity-fed well, and during the winter the units are air-cooled to bypass the problems created by the lower regional water table.[16]

On May 10, 2007, a fire started in the power plant module warehouse. Work was being done on the exterior of the building to install supports for an overhead door and the welding sparks fell inside the building, causing the fire. Since the building was vacant at the time, the fire was not immediately apparent. The building suffered moderate fire damage but none of the main power plant components were compromised. Burning insulation that fell on top of the power plant modules melted much of the electrical wiring along with the control panel. Due to the cold water running through the plant during the fire, no thermal breakdown of the modules’ oil or working fluid occurred. The working fluid used, R134a, is a non-flammable refrigerant and did not present a hazard due to accidental fluid release. The Chena crew was able to restart ORC#2 after a month, and ORC#1 was anticipated to be operational again in early July.[9]

From 2007-2010, produced temperatures from the production wells Well #7 and TG-8 steadily declined to 159° from 165°F. As a result, the overall electrical production of the geothermal power plant was reduced. This prompted the deep drilling of Well TG-12 during GRED III Phase II in order to respond to the temperature loss and locate a hotter resource with increased geothermal fluid flow. However, the well was drilled into an outflow zone and encountered a temperature reversal at 2,700 ft.[10]


Geology of the Area



Geologic Setting

Tectonic Setting: Non-Tectonic [12][5]

Controlling Structure: Fault Intersection, Intrusion Margins and Associated Fractures [19][5]

Topographic Features: [8]

Brophy Model: Type A: Magma-heated, Dry Steam Resource [12][5]

Moeck-Beardsmore Play Type: CV-2b: Plutonic - Inactive Volcanism, CV-3: Extensional Domain"CV-2b: Plutonic - Inactive Volcanism, CV-3: Extensional Domain" is not in the list of possible values (CV-1a: Magmatic - Extrusive, CV-1b: Magmatic - Intrusive, CV-2a: Plutonic - Recent or Active Volcanism, CV-2b: Plutonic - Inactive Volcanism, CV-3: Extensional Domain, CD-1: Intracratonic Basin, CD-2: Orogenic Belt, CD-3: Crystalline Rock - Basement) for this property.


Geologic Features

Modern Geothermal Features: Hot Springs [4]

Relict Geothermal Features:

Volcanic Age: Not related to Quaternary volcanism [12]

Host Rock Age: 90 Ma [19][5]

Host Rock Lithology: Granitic Pluton [4]

Cap Rock Age:

Cap Rock Lithology:


Figure 9. Geological setting of the Chena Hot Springs Geothermal Area [8]

The Chena Geothermal Area is located centrally within the Yukon-Tanana Upland, a region characterized by rounded mountain highlands between the Yukon and Tanana Rivers. The Chena Hot Springs are one of approximately 30 hot springs found in a 2,000-mile-long thermal belt, the CAHSB, extending from the Seward Peninsula to the Yukon Territory. The majority of the thermal springs along this trend are low- to moderate-temperature systems, typically located on the margin of a granitic pluton (Figure 9).[8] These plutons range from mid-Cretaceous to early Tertiary age and many have been identified with anomalously high concentrations of the radioactive elements uranium and thorium.[20] The Chena Geothermal Area is not related to Quaternary volcanism and has no known major structural features within a 30-mile radius.[8] [12]

The Chena Hot Springs are located at an elevation of 1,170 ft in the Monument Creek Valley. Mountains border this area to the southwest and northeast, reaching an altitude of ~3,500 ft.[8] The Chena granitic pluton, which hosts the Chena Hot Springs, has an areal extent of 5x40 km^2 and is surrounded by Paleozoic metamorphic rocks. The age of the Chena pluton was determined to be 59 Ma based on K-Ar dating of biotite from a monzogranite rock sample,[21] but subsequent sampling has indicated an original age around 90 Ma based Ar-Ar dating and hornblende spectral analysis.[20] Hydrothermal alteration exists in the plutonic rocks but no evidence of intense clay alteration due to steam is present.[8]

Based on the geological mapping, rock sampling, and surface and airborne geophysical measurements collected during the GRED III Phase I Project, a conceptual model and sequence of geological events for the Chena Geothermal Area has been proposed.[22] Studies of the Chena pluton indicate three distinct intrusive phases: the early Cretaceous, the mid-Cretaceous, and the early Tertiary. Kolker et al. have posited a mid-Cretaceous pluton underlain by a radioactive early Tertiary pluton. This early Tertiary pluton is hypothesized to have reset the Ar-Ar ratios in the hornblende of the mid-Cretaceous granite at 59 Ma, as measured by Biggar (1973).[21][20] Early Tertiary outcrop similar to the proposed pluton exists to the north and northeast of the Chena Geothermal Area and is correlated with radiometric measurements of anomalously high radioactivity. The radiometric data also assisted in the constraint of the southern boundary of the pluton, which is now accepted to be at Monument Creek as opposed to 2 km further to the south.[8] The airborne EM and surface resistivity data produced anomalies which were not consistent with one another nor with the thermal pattern recorded through well measurements, yielding largely inconclusive results. The magnetic measurements produced a signature typical of granitic terrains (i.e., relatively flat and featureless).[8]

The geothermal fluids at Chena contain high concentrations of boron, lithium, and fluorine, which is characteristic of early Tertiary granites measured in other regions of Interior Alaska. The depth and geometry of the Tertiary pluton is not constrained. However, the geothermal wells did not penetrate this pluton, indicating a depth greater than the maximum drilled depth of ~300 m.[5] This conceptual understanding of the Chena Geothermal Area indicates a favorable geological setting to host a geothermal system.[8]

Figure 10. Geological map of the Chena Hot Springs Geothermal Area, after Holdmann et al. 2006.[8]




Hydrothermal System


The Chena geothermal system consists of two distinct episodes of hydrothermal activity as depicted through fluid inclusion and alteration assemblage pattern analyses. The propylitic alteration phase likely occurred during the early Tertiary and is not related to the modern geothermal fluids. Lower reservoir temperature (80° - 120°C) hydrothermal alteration is related to the present-day geothermal system. Water samples analyzed by SMU revealed a minor variation between the isotopic composition of local meteoric water and the geothermal fluid, providing evidence that the geothermal fluids originated under modern climatic conditions.[5][8]

The main shallow upflow zone of the Chena Geothermal Area is 600 m long by 90 m wide. Stable isotope analysis indicates the geothermal fluids are of meteoric origin with a circulation time less than 3,000 years. The estimated depth of circulation of the system is hypothesized at 3,300 m and it is predicted that 120°C geothermal fluids should be encountered at approximately 500 - 1000 m depth. The Chena geothermal system is proposed as a fault/fracture-dominated geothermal system, although it is not associated with any major regional structural features.[12] A northwest-trending subvertical fault zone is the conduit for the geothermal fluid upwelling based on airborne resistivity maps and geological data. The deep thermal fluids are proposed to enter the shallow system approximately 500 m to the west of the hot springs, flowing to the east and mixing with groundwater to create a shallow convective system beneath the springs.[5][12]

The temperature-gradient hole drilling program yielded additional information regarding the hydrothermal system. Eleven temperature-gradient holes were drilled in addition to the eight shallow wells that were already drilled, and temperature and pressure logs were run in each hole and well. Select wells were flow-, interference- and injection-tested during the exploration program.[8] The temperature-gradient hole drilling program delineated production and injection zones, and enabled a better understanding of the connectivity of the reservoir.[12] Further deep drilling of Well TG-12 was carried out during the GRED III Phase II project, but a temperature reversal was encountered at 2,700 ft, and the anticipated temperatures of 200°F were not achieved. However, the information gained from Well TG-12 contributed to the reservoir model and conceptual understanding of the system.[10]


Heat Source


The crustal heat source of the Chena Geothermal System is due to the radioactive decay of uranium, thorium, and potassium within the early Tertiary pluton. Radiogenic heat production calculations indicate an anomalously high heat production value which may contribute to the elevated geothermal gradient at relatively shallow depth.[5][19] Helium isotope analysis confirms there is no magmatic or mantle input to the Chena geothermal system, providing further evidence of a crustal heat source.[19] The Chena Geothermal Area is a fault-dominated, low-temperature convective geothermal system with a high heat producing granite as the heat source.[5]


Geofluid Geochemistry



Geochemistry

Salinity (low): 282 [19][5]

Salinity (high): 388 [19][5]

Salinity (average): 335 [19][5]

Brine Constituents: Alkali-chloride type waters with elevated B, Li, and F concentrations, a pH of 9, and TDS between 282 - 288 ppm. [19][5]

Water Resistivity:


Geochemical analyses from the geothermal wells in the Chena Geothermal Area present a relatively consistent chemical composition of alkali-chloride type waters with a pH around 9 and elevated boron, lithium, and fluorine concentrations. The total dissolved solids concentration ranges between 282 - 388 ppm. The chalcedony geothermometer is the most appropriate geothermometer to apply for Chena Hot Springs because of the low temperature of the hot springs, the chalcedony identified in the geothermal well cuttings, and the lacking feldspar-mica assemblage in the reservoir rocks. A reservoir temperature of ~100°C was indicated. Fluid inclusion analyses suggest a reservoir temperature between 100 and 120°C.[5]


NEPA-Related Analyses (1)


Below is a list of NEPA-related analyses that have been conducted in the area - and logged on OpenEI. To add an additional NEPA-related analysis, see the NEPA Database.

CSV

Document # Analysis
Type
Applicant Application
Date
Decision
Date
Lead
Agency
Development
Phase(s)
Techniques
GFO-04-236b, GFO-10-367 Chena Hot Springs Resort DOE Golden Field Office Geothermal/Exploration Slim Holes


Exploration Activities (35)


Below is a list of Exploration that have been conducted in the area - and cataloged on OpenEI. Add.png Add a new Exploration Activity


Page Technique Activity Start Date Activity End Date Reference Material
2-M Probe Survey At Chena Geothermal Area (Wescott & Turner, 1982) 2-M Probe Survey 1973 1974


Aerial Photography At Chena Geothermal Area (Kolker, 2008) Aerial Photography 1979 1980


Aeromagnetic Survey At Chena Area (Erkan, Et. Al., 2008) Aeromagnetic Survey 2008


Aeromagnetic Survey At Chena Geothermal Area (Kolker, 2008) Aeromagnetic Survey 2005 2007


Airborne Electromagnetic Survey At Chena Area (Erkan, Et. Al., 2008) Airborne Electromagnetic Survey 2008 2008


Airborne Electromagnetic Survey At Chena Geothermal Area (Kolker, 2008) Airborne Electromagnetic Survey 2005 2007


Audio-Magnetotellurics At Chena Area (Erkan, Et. Al., 2008) Audio-Magnetotellurics


Audio-Magnetotellurics At Chena Geothermal Area (Holdmann, Et Al., 2006) Audio-Magnetotellurics 2005 2007


Data Acquisition-Manipulation At Chena Area (Erkan, Et. Al., 2008) Data Acquisition-Manipulation


Electromagnetic Soundings At Chena Geothermal Area (Wescott & Turner, 1982) Electromagnetic Sounding Techniques 1979 1980


Exploratory Boreholes At Chena Geothermal Area (Kolker, Et Al., 2006) Exploratory Boreholes 2005 2007


FLIR At Chena Geothermal Area (Holdmann, Et Al., 2006) FLIR 2005 2007


Field Mapping At Chena Geothermal Area (Kolker, 2008) Field Mapping 1973 1974


Field Mapping At Chena Geothermal Area (Waring, Et Al., 1917) Field Mapping 1917 1917


Flow Test At Chena Geothermal Area (Holdmann, Et Al., 2006) Flow Test 2005 2007


Fluid Inclusion Analysis At Chena Geothermal Area (Kolker, 2008) Fluid Inclusion Analysis 2005 2007


Geographic Information System At Chena Geothermal Area (Holdmann, Et Al., 2006) Geographic Information System 2005 2007


Geothermometry At Chena Geothermal Area (Kolker, 2008) Geothermometry 1973 1974


Ground Magnetics At Chena Geothermal Area (Kolker, 2008) Ground Magnetics 1973 1974


Injectivity Test At Chena Geothermal Area (Holdmann, Et Al., 2006) Injectivity Test 2005 2007


Isotopic Analysis At Chena Geothermal Area (Holdmann, Et Al., 2006) Isotopic Analysis- Fluid 2005 2007


Isotopic Analysis- Gas At Chena Geothermal Area (Kolker, Et Al., 2008) Isotopic Analysis- Fluid 2007 2007


Micro-Earthquake At Chena Geothermal Area (Holdmann, Et Al., 2006) Micro-Earthquake 2006 2007


Pressure Temperature Log At Chena Geothermal Area (Holdmann, Et Al., 2006) Pressure Temperature Log 2005 2007


Radiometrics At Chena Geothermal Area (Kolker, 2008) Radiometrics 2005 2007


Refraction Survey At Chena Geothermal Area (Wescott & Turner, 1982) Refraction Survey 1979 1980


Rock Sampling At Chena Geothermal Area (Kolker, 2008) Rock Sampling 1973 1974


Schlumberger Resistivity Soundings At Chena Geothermal Area (Wescott & Turner, 1982) DC Resistivity Survey (Schlumberger Array) 1979 1980


Soil Gas Sampling At Chena Geothermal Area (Kolker, 2008) Soil Gas Sampling 1979 1980


Soil Sampling At Chena Geothermal Area (Kolker, 2008) Soil Sampling 1979 1980


Surface Water Sampling At Chena Geothermal Area (Holdmann, Et Al., 2006) Surface Water Sampling 1980 1980


Surface Water Sampling At Chena Geothermal Area (Waring, Et Al., 1917) Surface Water Sampling 1917 1917


Thermal Gradient Holes At Chena Geothermal Area (EERE, 2010) Thermal Gradient Holes 2009 2010


Thermal Gradient Holes At Chena Geothermal Area (Erkan, Et Al., 2007) Thermal Gradient Holes 2005 2007


Thermal Gradient Holes At Chena Geothermal Area (Holdmann, Et Al., 2006) Thermal Gradient Holes 1998 2005

References


  1. Ruggero Bertani. 2005. World Geothermal Power Generation 2001-2005. Proceedings of World Geothermal Congress; Turkey: World Geothermal Congress.
  2. 2.0 2.1 2.2 400 kw Geothermal Power plant at Chena Hot Springs, Alaska
  3. 3.0 3.1 3.2 U.S. Geological Survey. 2008. Assessment of Moderate- and High-Temperature Geothermal Resources of the United States. USA: U.S. Geological Survey. Report No.: Fact Sheet 2008-3082.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Gerald Ashley Waring,Richard Bryant Dole,Alfred A. Chambers. 1917. Mineral Springs of Alaska. (!) : US Government Printing Office.
  5. 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 5.13 5.14 5.15 5.16 5.17 Geologic Setting of the Central Alaskan Hot Springs Belt: Implications for Geothermal Resource Capacity and Sustainable Energy Production
  6. 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 John W. Lund. 2006. Chena Hot Springs. Geo-Heat Center Quarterly Bulletin. 27(3):2-4.
  7. 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 8.13 8.14 8.15 Gwen Holdmann,Dick Benoit,David Blackwell. 2006. Integrated Geoscience Investigation and Geothermal Exploration at Chena Hot Springs, Alaska. (!) : Phase I final report prepared for the Dept. of Energy Golden Field Office under award DE-FC36-04GO14347.
  8. 9.0 9.1 9.2 9.3 9.4 9.5 Gwen Holdmann. 2007. The Chena Hot Springs 400kw Geothermal Power Plant: Experience Gained During the First Year of Operation. Chena Geothermal Power Plant Report, Chena Power Plant, Alaska. 1-9.
  9. 10.0 10.1 10.2 10.3 10.4 10.5 10.6 EERE. 2010. 4.2.1 GRED Drilling Award- GRED III Phase II. (!) : EERE.
  10. 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 Chena Power LLC.. 2007. 400kW Geothermal Power Plant at Chena Hot Springs, Alaska. Final Report prepared for Alaska Energy Authority. (!) .
  11. 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 Kamil Erkan,Gwen Holdman,David Blackwell,Walter Benoit. 2007. Thermal Characteristics of the Chena Hot Springs Alaska Geothermal System. In: PROCEEDINGS, Thirty-Second Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California. Stanford Geothermal Workshop; 2007; (!) . (!) : (!) ; p. (!)
  12. 2007. ALASKA ENERGY AUTHORITY Alaska Geothermal Development: A Plan. (!) : (!) .
  13. 14.0 14.1 Bernie Karl. 2010. GRED III Phase II. p.
  14. 15.0 15.1 15.2 15.3 15.4 Eugene M. Wescott,Donald L. Turner. 1982. Geothermal Energy Resource Assessment of Parts of Alaska. (!) . (!) .
  15. 16.0 16.1 Dick Benoit,Gwen Holdmann,David Blackwell. 2007. Low Cost Exploration, Testing, and Development of the Chena Geothermal Resource. GRC Transactions. 31:147-152.
  16. Joost J. Brasz,Bruce P. Biederman,Gwen Holdmann. 2005. Power Production from a Moderate-Temperature Geothermal Resource. In: GRC annual meeting; 2005; Reno, Nevada. (!) : (!) ; p. (!)
  17. 18.0 18.1 18.2 Bernie Karl,Ian-Michael Hebert,Jesse Warwick. 2009. Electric Power Generation Using Geothermal Fluid Coproduced from Oil and/or Gas Wells. GRC Transactions. 33: (!) .
  18. 19.0 19.1 19.2 19.3 19.4 19.5 19.6 19.7 Amanda M. Kolker,B.M. Kennedy,R.J. Newberry. 2008. Evidence for a Crustal Heat Source for Low-Temperature Geothermal Systems in the Central Alaskan Hot Springs Belt. GRC Transactions. 32:225-230.
  19. 20.0 20.1 20.2 Amanda M. Kolker,Rainer Newberry,Jessica Larsen,Paul Layer,Patrick Stepp. 2007. Geologic Setting of the Chena Hot Springs Geothermal System, Alaska. In: Proceedings of the Thirty-second Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, CA, USA. Stanford Geothermal Workshop; 2007; (!) . (!) : (!) ; p. 416-423
  20. 21.0 21.1 Norma Biggar. 1973. A Geological and Geophysical Study of Chena Hot Springs, Alaksa [M.Sc. Thesis]. [Fairbanks, Alaska]: University of Alaska.
  21. Amanda M. Kolker, Jess Larsen, Rainer Newberry, and Mary Keskinen. 2006. Chena Hot Springs GRED III Project: Final Report Geology, Petrology, Geochemistry, Hydrothermal Alteration, and Fluid Analyses. Fairbanks, AK: University of Alaska Fairbanks.


List of existing Geothermal Resource Areas.






Some of the content on this page was part of a case study conducted by: NREL Interns


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