Differential stress as a function of axial displacement for (a) granodiorite samples from a depth of 8406 ft, and (b) diorites from a depth of 7974 ft (from fig. 1)
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.
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