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At least 145 records · Page 8Linked to original sources
USGS1973

Resistivity, self‐potential, and induced‐polarization surveys of a vapor‐dominated geothermal system

The Mud Volcano area in Yellowstone National Park provides an example of a vapor‐dominated geothermal system. A test well drilled to a depth of about 347 ft penetrated the vapor‐dominated reservoir at a depth of less than 300 ft. Subsequently, 16 vertical electrical soundings (VES) of the Schlumberger type were made along a 3.7‐mile traverse to evaluate the electrical resistivity distribution within this geothermal field. Interpretation of the VES curves by computer modeling indicates that the vapor‐dominated layer has a resistivity of about 75–130 ohm‐m and that its lateral extent is about 1 mile. It is characteristically overlain by a low‐resistivity layer of about 2–6.5 ohm‐m, and it is laterally confined by a layer of about 30 ohm‐m. This 30‐ohm‐m layer, which probably represents hot water circulating in low‐porosity rocks, also underlies most of the survey at an average depth of about 1000 ft. Horizontal resistivity profiles, measured with two electrode spacings of an AMN array, qualitatively corroborate the sounding interpretation. The profiling data delineate the southeast boundary of the geothermal field as a distinct transition from low to high apparent resistivities. The northwest boundary is less distinctly defined because of the presence of thick lake deposits of low resistivities. A broad positive self‐potential anomaly is observed over the geothermal field, and it is interpretable in terms of the circulation of the thermal waters. Induced‐polarization anomalies were obtained at the northwest boundary and near the southeast boundary of the vapor‐dominated field. These anomalies probably are caused by relatively high concentrations of pyrite.

Wyoming↗
USGS1993

The Geysers-Clear Lake area, California: Thermal waters, mineralization, volcanism, and geothermal potential

Manifestations of a major thermal anomaly in the Geysers-Clear Lake area of northern California include the late Pliocene to Holocene Clear Lake Volcanics, The Geysers geothermal field, abundant thermal springs, and epithermal mercury and gold mineralization. The epithermal mineralization and thermal springs typically occur along high-angle faults within the broad San Andreas transform fault system that forms the western boundary of the North American plate in this area. The young volcanic rocks overlie Mesozoic marine rocks of the Great Valley sequence which have been thrust above the coeval Franciscan Complex and penecontemporaneously dropped back down along low-angle detachment faults.Many of the waters of the region are nonmeteoric as defined by their isotopic signature. One type of isotopically shifted water emerges from or near Great Valley sequence rocks and is the most chloride rich. It is interpreted to be evolved connate in origin. A second type, evolved meteoric water, has moderate chloride contents, high boron contents, and high B/Cl ratios and is found locally in Franciscan rocks, notably at the Sulphur Bank mercury mine, where it probably results from near-closed-system, repeated boiling of meteoric water in host rocks that also contribute organic components to the water. At the Sulphur Bank mine fracturing of otherwise impermeable Franciscan rocks by faulting has created a localized zone of permeability in which thermal water boils repeatedly with limited venting to the surface. Boron-rich fluids were apparently present at depth in The Geysers geothermal field when intrusion of silicic magma occurred, because the concealed intrusion of felsite is surrounded by a halo of tourmaline-bearing hornfels. The volume of this poorly dated early to middle Quaternary intrusive body probably exceeds the 100 km 3 of erupted Clear Lake Volcanics. Similar intrusions may have occurred in the eastern part of the area at Wilbur Springs and the McLaughlin mine, where gold deposition and evidence of hydrothermal phenomena suggest more magmatic activity than is indicated by the small exposed bodies of early Quaternary basaltic lava. The Clear Lake Volcanics are the present locus of volcanism in the northern Coast Ranges and progressively older volcanic centers occur to the south. Geophysical data suggest that a large silicic magma body may be centered north of The Geysers steam field, providing the heat for the geothermal field.Geothermal power production has peaked at The Geysers and pressure declines indicate significant depletion of the fluid resource. The vapor-dominated field evolved from a preexisting hydrothermal system within fractured, otherwise impermeable Franciscan metamorphic rocks. A deep water table of saline fluid has been postulated to be present under the steam field, but no chloride-rich water has been found at drillable depth. We propose that recently discovered, isotopically shifted steam in the northwest Geysers area indicates the presence not of deep connate water but xather of boiled-down, boron-rich Franciscan evolved meteoric water. This water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at The Geysers field or from the main Clear Lake volcanic field.

Economic Geology↗
USGS2012

Temperature logging of groundwater in bedrock wells for geothermal gradient characterization in New Hampshire, 2012

The U.S. Geological Survey, in cooperation with the New Hampshire Geological Survey, measured the fluid temperature of groundwater in deep bedrock wells in the State of New Hampshire in order to characterize geothermal gradients in bedrock. All wells selected for the study had low water yields, which correspond to low groundwater flow from fractures. This reduced the potential for flow-induced temperature changes that would mask the natural geothermal gradient in the bedrock. All the wells included in this study were privately owned, and permission to use the wells was obtained from homeowners before logging. Maximum groundwater temperatures at the bottom of the logs were between 11.7 and 17.3 degrees Celsius. Geothermal gradients were generally higher than typically reported for other water wells in the United States. Some of the high gradients were associated with high natural gamma emissions. Groundwater flow was discernible in 5 of the 10 wells studied but only obscured the portion of the geothermal gradient signal where groundwater actually flowed through the well. Temperature gradients varied by mapped bedrock type but can also vary by differences in mineralogy or rock type within the wells.

New Hampshire↗
USGS2014

Geophysical logging of bedrock wells for geothermal gradient characterization in New Hampshire, 2013

The U.S. Geological Survey, in cooperation with the New Hampshire Geological Survey, measured the fluid temperature of groundwater and other geophysical properties in 10 bedrock wells in the State of New Hampshire in order to characterize geothermal gradients in bedrock. The wells selected for the study were deep (five ranging from 375 to 900 feet and five deeper than 900 feet) and 6 had low water yields, which correspond to low groundwater flow from fractures. This combination of depth and low water yield reduced the potential for flow-induced temperature changes that would mask the natural geothermal gradient in the bedrock. All the wells included in this study are privately owned, and permission to use the wells was obtained from landowners before geophysical logs were acquired for this study. National Institute of Standards and Technology thermistor readings were used to adjust the factory calibrated geophysical log data. A geometric correction to the gradient measurements was also necessary due to borehole deviation from vertical. Maximum groundwater temperatures at the bottom of the logs ranged from 11.2 to 15.4 degrees Celsius. Geothermal gradients were generally higher than those typically reported for other water wells in the United States. Some of the high gradients were associated with high natural gamma emissions. Groundwater flow was discernible in 4 of the 10 wells studied but only obscured the part of the geothermal gradient signal where groundwater actually flowed into, out of, or through the well. Temperature gradients varied by mapped bedrock type but can also vary by localized differences in mineralogy or rock type within the wells.

New Hampshire↗
USGS2006

Physical properties of two core samples from Well 34-9RD2 at the Coso geothermal field, California

The Coso geothermal field, located along the Eastern California Shear Zone, is composed of fractured granitic rocks above a shallow heat source. Temperatures exceed 640 ?F (~338 ?C) at a depth of less than 10000 feet (3 km). Permeability varies throughout the geothermal field due to the competing processes of alteration and mineral precipitation, acting to reduce the interconnectivity of faults and fractures, and the generation of new fractures through faulting and brecciation. Currently, several hot regions display very low permeability, not conducive to the efficient extraction of heat. Because high rates of seismicity in the field indicate that the area is highly stressed, enhanced permeability can be stimulated by increasing the fluid pressure at depth to induce faulting along the existing network of fractures. Such an Enhanced Geothermal System (EGS), planned for well 46A-19RD, would greatly facilitate the extraction of geothermal fluids from depth by increasing the extent and depth of the fracture network. In order to prepare for and interpret data from such a stimulation experiment, the physical properties and failure behavior of the target rocks must be fully understood. Various diorites and granodiorites are the predominant rock types in the target area of the well, which will be pressurized from 10000 feet measured depth (MD) (3048m MD) to the bottom of the well at 13,000 feet MD (3962 m MD). Because there are no core rocks currently available from well 46A-19RD, we report here on the results of compressive strength, frictional sliding behavior, and elastic measurements of a granodiorite and diorite from another well, 34-9RD2, at the Coso site. Rocks cored from well 34-9RD2 are the deepest samples to date available for testing, and are representative of rocks from the field in general.

Open-File Report↗
USGS1974

Geothermal systems of northern Nevada

Hot springs are numerous and nearly uniformly distributed in northern Nevada. Most occur on the flanks of basins, along Basin and Range (late Miocene to Holocene) faults, while some occur in the inner parts of the basins. Surface temperatures of the springs range from slightly above ambient to, boiling; some springs are superheated. Maximum subsurface water temperatures calculated on the basis of quartz solubility range as high as 252?C, although most are below 190?C. Flows range from a trickle to several hundred liters per minute. The Nevada geothermal systems differ markedly from the power-producing system at The Geysers, Calif., and from those areas with a high potential, for power production (e.g., Yellowstone Park, Wyo.; Jemez Mountains, N. Mex.). These other systems are associated with Quaternary felsic volcanic rocks and probably derive their heat from cooling magma rather high in the crust. In northern Nevada, however, felsic volcanic rocks are virtually all older than 10 million years, and. analogous magmatic heat sources are, therefore, probably lacking. Nevada is part of an area of much higher average heat flow than the rest of the United States. In north-central Nevada, geothermal gradients are as great as 64?C per kilometer in bedrock and even higher in basin fill. The high gradients probably result from a combination of thin crust and high temperature upper mantle. We suggest that the geothermal systems of northern Nevada result from circulation of meteoric waters along Basin and Range faults and that their temperature chiefly depends upon (1) depth of circulation and (2) the geothermal gradient near the faults.

Open-File Report↗
USGS1976

Basic data from five core holes in the Raft River geothermal area, Cassia County, Idaho

Studies of the geothermal aspect-of the Bridge area of the Raft River basin in south-central Idaho (fig. 1) by the U.S. Geological Survey began in 1972 when Young and Mitchell (1973) made a geochemical and geologic reconnaissance of selected thermal waters in Idaho. The Bridge area had been designated the Frazier known geothermal resource area (Frazier KGRA) by the U.S. Geological Survey (Godwin and others-, 1971) . Since 1972, several units of the Geological Survey have studied the area to provide data for the U.S. Energy Research and Development Administration, which proposes to ascertain whether the geothermal resource can be developed for power generation and other uses. The studies include geologic mapping, geophysical surveys, water sampling, test drilling, and studies of all available drill- hole data. A list of reports already prepared on the area is included with this report. Core drilling of five holes began in August 1974 and was completed in March 1975. These holes are referred to as intermediate-depth core holes, principally because in the spring of 1974, 35 auger holes 25 to 98 feet (7.6 to 30 meters) were completed in the area (Crosthwaite, 1974), and the Aerojet Nuclear Company, under the auspices of the U.S. Energy Research and Development Administration, was planning some deep drilling 4,000 to 6,000 feet (1,200 to 1,800 meters) (fig. 1). The purpose of the core drilling was to provide information to test geophysical interpretations of the subsurface structure and lithology and to provide hydrologic and geologic data on the shallow part of the geothermal system. Samples of the core were made available to several divisions and branches of the Geological Survey and to people and agencies outside the Survey. This report presents the basic data from the core holes that had been collected to September 1, 1975, and includes lithologic and geophysical well logs, chemical analyses of water (table 1), and laboratory analyses of cores (table 2) that were completed as of the above date. The data were collected by the Idaho District office, Hydrologic Laboratory, Borehole Geophysics Research Project, and Drilling, Sampling, and Testing Section, all of the Water Resources Division, and the Branch of Central Environmental Geology of the Geologic Divison.

Idaho↗
USGS1977

GEOTHERM user guide

GEOTHERM is a computerized geothermal resources file developed by the U.S. Geological Survey. The file contains data on geothermal fields, wells, and chemical analyses from the United states and international sources. The General Information Processing System (GIPSY) in the IBM 370/155 computer is used to store and retrieve data. The GIPSY retrieval program contains simple commands which can be used to search the file, select a narrowly defined subset, sort the records, and output the data in a variety of forms. Eight commands are listed and explained so that the GEOTHERM file can be accessed directly by geologists. No programming experience is necessary to retrieve data from the file.

Open-File Report↗
USGS2012

Using micro-seismicity and seismic velocities to map subsurface geologic and hydrologic structure within the Coso geothermal field, California

Geothermal reservoirs derive their capacity for fluid and heat transport in large part from faults and fractures. Micro-seismicity generated on such faults and fractures can be used to map larger fault structures as well as secondary fractures that add access to hot rock, fluid storage and recharge capacity necessary to have a sustainable geothermal resource. Additionally, inversion of seismic velocities from micro-seismicity permits imaging of regions subject to the combined effects of fracture density, fluid pressure and steam content, among other factors. We relocate 14 years of seismicity (1996-2009) in the Coso geothermal field using differential travel times and simultaneously invert for seismic velocities to improve our knowledge of the subsurface geologic and hydrologic structure. We utilize over 60,000 micro-seismic events using waveform cross-correlation to augment to expansive catalog of P- and S-wave differential travel times recorded at Coso. We further carry out rigorous uncertainty estimation and find that our results are precise to within 10s of meters of relative location error. We find that relocated micro-seismicity outlines prominent, through-going faults in the reservoir in some cases. We also find that a significant portion of seismicity remains diffuse and does not cluster into more sharply defined major structures. The seismic velocity structure reveals heterogeneous distributions of compressional (Vp) and shear (Vs) wave speed, with Vp generally lower in the main field when compared to the east flank and Vs varying more significantly in the shallow portions of the reservoir. The Vp/Vs ratio appears to outline the two main compartments of the reservoir at depths of -0.5 to 1.5 km (relative to sea-level), with a ridge of relatively high Vp/Vs separating the main field from the east flank. In the deeper portion of the reservoir this ridge is less prominent. Our results indicate that high-precision relocations of micro-seismicity can provide useful insight into: 1) prominent structural features, faults and fractures that contribute to the flow of fluid and heat in the reservoir; 2) diffuse seismicity throughout the reservoir representing fractures that likely contribute to the overall permeability, storage and heat exchange capacity of the reservoir, but which are not confined to prominent faults; and 3) seismic velocities that outline the major hydrologic compartments within the Coso geothermal field.

Coso geothermal field↗
USGS2013

Correlation of geothermal springs with sub-surface fault terminations revealed by high-resolution, UAV-acquired magnetic data

There is widespread agreement that geothermal springs in extensional geothermal systems are concentrated at fault tips and in fault interaction zones where porosity and permeability are dynamically maintained (Curewitz and Karson, 1997; Faulds et al., 2010). Making these spatial correlations typically involves geological and geophysical studies in order to map structures and their relationship to springs at the surface. Geophysical studies include gravity and magnetic surveys, which are useful for identifying buried, intra-basin structures, especially in areas where highly magnetic, dense mafic volcanic rocks are interbedded with, and faulted against less magnetic, less dense sedimentary rock. High-resolution magnetic data can also be collected from the air in order to provide continuous coverage. Unmanned aerial systems (UAS) are well-suited for conducting these surveys as they can provide uniform, low-altitude, high-resolution coverage of an area without endangering crew. In addition, they are more easily adaptable to changes in flight plans as data are collected, and improve efficiency. We have developed and tested a new system to collect magnetic data using small-platform UAS. We deployed this new system in Surprise Valley, CA, in September, 2012, on NASA's SIERRA UAS to perform a reconnaissance survey of the entire valley as well as detailed surveys in key transition zones. This survey has enabled us to trace magnetic anomalies seen in ground-based profiles along their length. Most prominent of these is an intra-basin magnetic high that we interpret as a buried, faulted mafic dike that runs a significant length of the valley. Though this feature lacks surface expression, it appears to control the location of geothermal springs. All of the major hot springs on the east side of the valley lie along the edge of the high, and more specifically, at structural transitions where the high undergoes steps, bends, or breaks. The close relationship between the springs and structure terminations revealed by this study is unprecedented. Collecting magnetic data via UAS represents a new capability in geothermal exploration of remote and dangerous areas that significantly enhances our ability to map the subsurface.

California↗
USGS2018

Strategic and critical metals in produced geothermal fluids from Nevada and Utah

Herein we summarize the results of an investigation dealing with the concentrations and inventories of strategic, critical and valuable materials (SCVM) in produced fluids from geothermal and hydrocarbon reservoirs (50-250° C) in Nevada and Utah. Water samples were collected from thirty-four production wells across eight geothermal fields, the Uinta Basin oil/gas province in northeast Utah, and the Covenant oil field in southwestern Utah; additional water samples were collected from six hot springs in the Sevier Thermal Belt in southwestern Utah. Most SCVM concentrations in produced waters range from <0.1 to 100 µg/kg; the main exception is lithium, which has concentrations that range from <1000 to 25,000 ug/kg. Relatively high concentrations of gallium, germanium, scandium, selenium, and tellurium are measured too. Geothermal waters contain very low concentrations of REEs, below analytical detections limits (0.01 µg/kg), but the concentrations of lanthanum, cerium, and europium range from 0.05 to 5 µg/kg in Uinta basin waters. Among the geothermal fields, the Roosevelt Hot Spring reservoir appears to have the largest inventories of germanium and lithium, and Patua appears to have the largest inventories of gallium, scandium, selenium, and tellurium. By comparison, the Uinta basin has larger inventories of gallium. The concentrations of gallium, germanium, lithium, scandium, selenium, and tellurium in produced waters appear to be partly related to reservoir temperature and concentrations of total dissolved salts. The relatively high concentration and large inventory of lithium occurring at Roosevelt Hot Springs may be related to granitic-gneissic crystalline rocks, which host the reservoir. Analyses of calcite scales from Dixie Valley indicate enrichments in cobalt, gallium, gold, palladium, selenium and tellurium, and these metals appear to be depositing at deep levels in production wells due to boiling. Comparisons with SCVM mineral deposits suggest that brines in sedimentary basins, or derived from lacustrine evaporites, enable aqueous transport of gallium, germanium, and lithium.

Conference Paper↗
USGS2019

Integrating magnetotellurics, soil gas geochemistry and structural analysis to identify hidden, high enthalpy, extensional geothermal systems

We applied magnetotellurics (MT), diagnostic structural affiliations, soil gas flux, and fluid geochemistry to assist in identifying hidden, high-enthalpy geothermal systems in extensional regimes of the U.S. Great Basin. We are specifically looking for high-angle, low-resistivity zones and dilatant geologic structures that can carry fluids from magmatic or high-grade metamorphic conditions in the deep crust upward to exploitable depths, and to verify the nature of the deep sources through soil gas and fluid compositions. The project was motivated by prior MT transect coverage of western and central Nevada centered upon the Dixie Valley producing geothermal system where such favorable indicators were first recognized. The high-angle MT structures are taken to be fluidized fault zones connecting deep magmatic/metamorphic activity with the geothermal system, but the concept required verification by testing at other systems. The project was set up with a two-phased organization. Phase I was carried out at the McGinness Hills system, central Nevada, where Ormat Inc flagship power facility is located and a considerable amount of pre-existing data were available. Resistivity models along MT transects also showed a strong low-resistivity upwelling originating from interpreted deep crustal magmatic underplating. Controlling structures on production as indicated by Ormat data and our new mapping were favorable to dilatancy, comprising an accommodation zone between major normal faults of opposing dip. A 3D MT survey and inversion confirmed the existence of the steep low-resistivity zone dipping ESE toward the deep crust and placed N-S bounds upon the feature. In cooperation with Ormat personnel, we sampled well fluids from production intervals for He isotope composition. Elevated 3He was verified through mass spectrometry analysis confirming a magmatic connection with the producing system. High CO2 soil gas flux including possibly metamorphic 13C and 14C component was measured over the area of dilatant structures. Hence, the triad of indicators posed above was confirmed in Phase I. Subsequently, Phase II of the project proceeded in the greenfield Kumiva-Blackrock Desert district of northwestern Nevada to see if a new system could be identified. Transect MT data also showed a low-resistivity upwelling originating from interpreted deep crustal magmatic underplating. An MT survey of 131 sites was imaged through 3D inversion using an in-house, DOE-supported finite element algorithm. Low resistivity upwellings that warranted follow up study occur under the flanks of the Seven Troughs Range, under Kumiva Playa immediately west of the Blue Wing Mountains, and under northern Granite Springs Valley. Structural assessment of the project area by Co-I J. Faulds at UNR provided numerous favorable Quaternary fault settings, which were correlated to the MT upwelling structures. Soil CO2 gas flux anomalies generally were not large but did show correlation with resistivity upwelling structure and favorable geological structures. Isotope analyses showed presence of possible inorganic/metamorphic 13C but 14C concentrations did not exceed background values. We view the initial concept of a confluence of low-resistivity upwelling, favorably dilatant 3D geological structure, and elevated soil gas flux including 13C component to be supported by the further evidence of this project although the indicators in the Phase II study were more diffuse. Mass balance calculations based upon 3He R/Ra values indicates that the proportion of magmatic fluids in a producing system is fairly low, 10-15% by volume. We suggest that the diagnostic MT geophysical structures denote zones of concentrated extensional deformation that increases permeability, potentially enabling a circulating upper crustal geothermal system, while at the same time connecting telltale deep component signatures to the upper crust. The northern Granite Springs Valley structure is receiving followup stu

Nevada↗
USGS2020

Preliminary report on applications of machine learning techniques to the Nevada geothermal play fairway analysis

We are applying machine learning (ML) techniques, including training set augmentation and artificial neural networks, to mitigate key challenges in the Nevada play fairway project. The study area includes ~85 active geothermal systems as potential training sites and >12 geologic, geophysical, and geochemical features. The main goal is to develop an algorithmic approach to identify new geothermal systems in the Great Basin region. Major objectives include: 1) integrate ML techniques into the geothermal community; 2) develop open community datasets, whereby all play fairway and ML datasets and algorithms are publicly released and available for modification by various user groups; 3) identify data acquisition targets with high value for future work; 4) identify new signatures to detect blind geothermal systems; and 5) foster new capabilities for characterizing subsurface temperature and permeability. Initially, ML techniques are being applied to the same play fairway datasets and workflow. ML will then be applied to both enhanced and additional datasets, with modification of the PFA workflow to incorporate the new datasets. Finally, ML will be applied to define new workflows using the enhanced and additional datasets. An algorithmic approach that empirically learns to estimate weights of influence for diverse parameters can potentially scale and perform better than the play fairway analysis. Initial work on this project has involved 1) evaluating potential positive and negative training sites, 2) transformation of datasets into formats suitable for ML, and 3) initial development and testing of ML techniques.

Nevada↗
USGS2023

New high resolution airborne geophysical surveys in Nevada And California for geothermal and mineral resource studies

The U.S. Geological Survey (USGS) and the Department of Energy (DOE) are collaborating to acquire high-resolution airborne magnetic and radiometric data to support geologic and geophysical mapping and modeling that will assist geothermal and critical mineral studies. Coordinated with these efforts are programs supporting geologic mapping and airborne LiDAR (light detection and ranging) surveys that yield detailed surface topographic models of the terrain over the same regions spanned by the geophysical surveys. The collaboration leverages resources from the USGS and DOE to acquire large regional datasets that will provide fundamental data necessary to map surface and subsurface geology and structure to benefit mineral and resource program objectives of both agencies. Such regionally uniform datasets are important for geothermal research to assist in identifying geologically favorable settings and as invaluable inputs in predictive models targeting undiscovered resources that use knowledge-driven (e.g., play fairway analysis) or data-driven approaches (e.g., machine-learning methods) to reduce risk associated with resource exploration. These data will also serve a wide range of other related activities from hazard (earthquake, volcano, landslide, environmental) and resource (water, mineral, energy) studies, to mapping and land management. Surveys were conducted in two areas that were selected because they host substantial geothermal and mineral potential in California and Nevada. The data will aid several ongoing USGS and DOE projects aimed at characterizing geothermal and mineral systems, understanding the factors controlling their occurrence, and improving future national resource assessments. The first of these surveys (referred to as GeoDAWN) was collected over northern and western Nevada and eastern California and spans areas of major resource potential associated with the Walker Lane and western Great Basin. This includes Clayton Valley, which hosts substantial lithium brine and clay resources, and the Humboldt Mafic Complex, which constitutes a potentially important resource of critical minerals (including cobalt, rare earth elements, platinum group elements, iron, chromium, nickel, and copper). The second survey area (referred to as GeoFlight) is focused over the Salton Trough in southern California that contains some of the largest and hottest known hydrothermal systems in the world, as well as a substantial lithium brine resource that could potentially meet the nation’s lithium demand for electric vehicles. Data from both surveys will be made publicly available through USGS publications and online data repositories. Future efforts under this collaboration are presently being evaluated and may involve acquisition of other data sets such as airborne gravity, electromagnetic or hyperspectral data to address research targets.

Conference Paper↗
USGS2025

Update of the 2008 provisional Enhanced Geothermal Systems (EGS) assessment for the Great Basin, USA

In response to the Energy Act of 2020, the U.S. Geological Survey (USGS) is updating the Enhanced Geothermal Systems (EGS) resource assessment for the Great Basin, USA. The previous 2008 provisional assessment estimated how much electricity could be generated from EGS resources of the western United States using models of electric-grade heat, models of heat extraction over time, and estimates of how much rock might be stimulated to produce viable amounts of heat. Herein, a similar conceptual strategy is applied, using updated models of heat extraction as a function of fracture spacing and well distance. Previously used reservoir heat delivery models are updated to have a dependence on fracture and well spacing, potentially improving future estimates of EGS resources as ongoing research provides a better understanding about the success of reservoir stimulation as a function of geology and location. For a range of well distances (250-1000 m) and fracture spacings (1-50 m), heat extraction efficiency ranges from 25-62%, demonstrating the importance of accounting for the most likely results of proven viable fracturing technologies. Although fracturing is important, the biggest uncertainty by far in estimating the EGS resource for the Great Basin is estimating which geologic units at what depths can be stimulated sufficiently to produce geothermal energy economically and efficiently. Uncertainties in these factors yield estimates that range over two orders of magnitude with an upper limit of ~174 terawatts-thermal (TWth) produced for 30 years from the upper 7 km of the crust. This upper limit would require significant technological advances to access most of the electric-grade resource across the Great Basin. Assuming that 1% of this estimate will be accessible in the next few decades gives a resource estimate similar to that made in the 2008 provisional assessment. These estimated EGS heat extraction rates far exceed ( greater than 100x) the natural geothermal heat production rate, thus geothermal electricity production at these rates might not be sustainable unless heat is also recharged from other sources (e.g., excess solar energy when supply exceeds demand). In addition to assessment maps and cumulative estimates, the new models of fractured reservoirs developed herein can be used to estimate steady power production given a set of fractures and well spacing, and estimates can be made for setback distances to ensure no thermal interference with nearby powerplants.

Arizona, California, Idaho, Nevada, Oregon, Utah↗
USGS2025

Potential for co-production of lithium and geothermal resources in the Gulf Coast

Lithium brine extractions and geothermal resource developments often are not economically viable as standalone projects, but they May become cost effective when the potential for both resources exist within the same reservoir. Subsurface datasets were analyzed to identify areas in the U.S. Gulf Coast region with potential for lithium brine and geothermal heat recovery. Temperature, lithium brine content, and reservoir quality data for thirty-four depositional units were evaluated using spatial analysis to interpret high-grade areas where both resources likely coexist. For sedimentary geothermal systems, potential resource areas are sorted by resource grade: as low temperature (<90°C, direct use potential), moderate temperature (90–150°C, direct use and electricity generation), and high temperature (>150°C, primarily electricity generation). Lithium resources were defined by Li lithium brine concentrations in parts per million (ppm): low potential (<100ppm), moderate potential (100–200ppm), and high potential (>200ppm). Reservoir quality affects the viability of both resources and is evaluated using interpreted lithofacies that describe the depositional environments of each unit. Using the results, a series of play fairway analysis maps were generated to support regional evaluations of lithium and geothermal resources and to identify areas of interest for detailed, prospect-scale studies.

Alabama, Florida, Georgia, Louisiana, Mississippi,↗
USGS1973

Galerkin finite-element simulation of a geothermal reservoir

The equations describing fluid flow and energy transport in a porous medium can be used to formulate a mathematical model capable of simulating the transient response of a hot-water geothermal reservoir. The resulting equations can be solved accurately and efficiently using a numerical scheme which combines the finite element approach with the Galerkin method of approximation. Application of this numerical model to the Wairakei geothermal field demonstrates that hot-water geothermal fields can be simulated using numerical techniques currently available and under development.

Geothermics↗
USGS1979

Preliminary isotopic studies of fluids from the Cerro Prieto geothermal field

Preliminary isotopic studies of Cerro Prieto geothermal fluids and earlier studies of Mexicali Valley ground waters suggest local recharge of the geothermal system from the area immediately to the west. Oxygen isotope exchange of water with reservoir rock minerals at temperatures increasing with depth has produced fluids with oxygen-18 contents increasing with depth, and pressure drawdown in the southeastern part of the field has allowed lower oxygen-18 fluids to invade the production aquifer from above. The contents of tritium and carbon-14 in the fluid suggest only that the age of the fluid is between 50 and 10,000 years. The isotopic compositions of carbon and sulfur are consistent with a magmatic origin of these elements but a mixed sedimentary-organic origin appears more likely for carbon and is also possible for sulfur. Investigations of the isotopic compositions of geothermal and cold ground waters continue and are being expanded as fluids become available and as separation and analysis methods are improved. ?? 1979.

Geothermics↗