Abstract

The Cove Fort-Sulphurdale KGRA is part of one of the largest thermal anomalies in the western United States. Since 1975 an extensive data base has been developed which includes the results of detailed and regional geologic, gravity, magnetic, seismic, and resistivity investigations. Geologic studies have delineated the major tectonic elements of the thermal system and have led to the recognition of large-scale gravitational glide blocks that act as a leaky cap to portions of the geothermal system.

Gravity and magnetic data have delineated major throughgoing structures beneath alluvium and basalt cover, and have indicated the importance of the Cove Fort-Beaver graben in localizing the geothermal reservoir. The presence of these structures and a high level of microearthquake activity suggest other target areas within the larger thermal anomaly. Electrical resistivity surveys and thermal gradient holes both contribute to the delineation of the known reservoir.

Four deep exploration wells which test the geothermal system were drilled between 1975 and 1979. One well, CFSU 42-7, recorded temperatures of 178°C. The high cost of drilling, high corrosion rates, low reservoir pressures, and the apparent limited extent of the high-temperature reservoir led to a premature conclusion in 1980 that the field was not economic for large-scale electric power production. More recent drilling in the vicinity of CFSU 42-7 resulted in the discovery of high-temperature (2Q0°C?) geothermal fluids at a depth of approximately 350 m. A well-head generator was installed and power production is expected in 1985. Additional development of the geothermal reservoir is anticipated in the 1985 to 1987 time frame.