Known Geothermal Resource Area Research Articles

Improved Preproduction Conceptual‐Numerical Model of the Roosevelt Geothermal Field using Geological, Geochemical and Structural Information

AbstractThe Roosevelt Hot Springs Known Geothermal Resource Area (KGRA) is a Basin and Range‐type geothermal resource, which is located in southwestern Utah. The integrated multicomponent geothermometry (IMG) approach is used to estimate the reservoir temperature at the Roosevelt Hot Springs KGRA. Geothermometric modeling results indicate the deep reservoir temperature is approximately 284.6°C. A conceptual model of the Roosevelt Hot Spring KGRA is provided through integrating the various pieces of exploration information, including the geological data, geothermometric results, temperature well log and field evidence. A two‐dimensional cross‐sectional model was thus built to quantitatively investigate the coupled thermal‐hydraulic processes in the Roosevelt geothermal field. By matching the preproduction temperature log data of deep wells, parameters controlling flow and heat transport are identified. The method and model presented here may be useful for other geothermal fields with similar conditions.

Hydrologic investigations in the Mammoth Corridor, Yellowstone National Park and vicinity, U.S.A.

The Mammoth Corridor in and adjacent to Yellowstone National Park encompasses a N-S alignment of geothermal features that extends from the Norris Geyser Basin adjacent to the Yellowstone caldera through Mammoth Hot Springs to the Corwin Springs Known Geothermal Resources Area (KGRA). Thermal springs in this region discharge water that ranges from NaKCl, silica-depositing type to CaNaHC0 3SO 4, travertine-depositing type. Although only a few relatively shallow wells have been drilled in the corridor, the region is of special interest because of the environmental issues associated with potential geothermal development adjacent to Yellowstone National Park. The U.S. Geological Survey conducted an intensive hydrogeologic study of this region during 1988–1990 and continued to collect hydrologic and geophysical data until 1994. The results of these investigations document the rates of discharge of thermal water and heat within the corridor, evidence for a magmatic heat source beneath the Mammoth Hot Springs area, and evidence for separate geothermal systems associated with Mammoth Hot Springs and with thermal waters discharging in the KGRA in the vicinity of La Duke Hot Springs. These investigations also indicate that limited development of the 70°C geothermal resource in the La Duke area would not affect thermal springs in Yellowstone National Park.

Simultaneous inversion modeling of gravity and aeromagnetic data applied to a geothermal study in Utah

Aeromagnetic and gravity surveys were conducted in the Black Rock Desert, Utah to assess the geothermal potential of the Meadow‐Hatton Known Geothermal Resource Area (KGRA). The presence of basalt flows less than 1000 yr old and a 400 000 yr old rhyolite dome suggested that a hot intrusive body, which should be detectable in both types of potential field data, may provide the heat source for hot springs in the study area. A simultaneous inversion computer program was developed as part of this study to model these potential field data. The resulting models indicate hydrothermal alteration about the hot springs extending to a depth of approximately 1 km. Normal faults above a low‐angle detachment appear to reach a depth of approximately 4 km and provide a path for the circulation of groundwater in the area. No evidence for a buried igneous body was found in the study area, and it is therefore concluded that the migration of fluids along the deep faults is sufficient to account for the water temperatures estimated for the KGRA.

Geothermal environmental assessment behaviour of selected geothermal brine contaminants in plants and soils

The behaviour of selected elements found in geothermal fluids of the Roosevelt Hot Springs known geothermal resource area (KGRA) was investigated in plant and soil systems. The kinetics of these potential environmental contaminants were studied by using soil columns and selected cultivated and native plant species. The data collected indicate that, of the 26 elements examined, lithium is the best indicator of geothermal contamination. This element, which occurs in the fluids at concentrations exceeding 25.0 parts per million (ppm), was readily detected in and through a variety of different test soils. The plant species, which were exposed via a number of rooting media including soils, vermiculite, and hydroponic solution, absorbed and translocated lithium to all aerial plant parts. The greatest lithium concentration occurred in hydroponically grown tomatoes where the leaves, stems, and fruit contain 914.5±35.8 ppm, 106.5±3.2 ppm, and 35.7±4.8 ppm of this element, respectively. Two native species — four-winged saltbush, A triplex canescens, and bitterbush, Purshia tridentata — appear to be good biological indicators since they accumulated nearly twice as much lithium, 309.8±29.9 ppm and 226.0±5.8 ppm, respectively, as did other native species tested.

Three‐dimensional Q−1 model of the Coso Hot Springs Known Geothermal Resource Area

Observations of teleseismic P waves above geothermal systems exhibit travel time delays and anomalously high seismic attenuation, which is extremely useful in estimating the thermal regime and the potential of the system. A regional telemetered network of sixteen stations was operated by the U.S. Geological Survey in the Coso Hot Springs Known Geothermal Resources Area (KGRA) for such studies from September 1975 to October 1976. Subsequently, they deployed a portable Centipede array of 26 three‐component stations near the center of the anomaly. The seismograms of 44 events recorded by the telemetered array and nine events by the Centipede array were analyzed using the reduced spectral ratio technique to determine the differential attenuation factor δt* for the events recorded with the highest signal‐to‐noise ratio. The δt* variation observed across the Coso Hot Springs KGRA were small (<0.2 s). A three‐dimensional generalized linear inversion of the δt* observations was performed using a three‐layer model. A shallow zone of high attenuation exists within the upper 5 km in a region bounded by Coso Hot Springs, Devils Kitchen, and Sugarloaf Mountain probably corresponding to a shallow vapor liquid mixture or ‘lossy’ near surface lithology. No zones of significantly high attenuation occur between 5‐ and 12‐ km depth. Between the depth of 12–20 km a thick zone of high attenuation (Q <50) exists, offset toward the east from the surface anomaly.