The Pyramid Lake area lies in the NW part of the Great Basin, which contains the greatest concentration of geothermal fields in the western U.S.. GPS geodetic data indicate that extensional strain rates are higher in this region than elsewhere in the Great Basin. This probably results from the northwestward termination of the Walker Lane, a system of dextral faults currently accommodating ~20% of the Pacific-North America relative motion, and the progressive transfer of dextral shear to WNW extension in the region. Enhanced extension favors dilation on normal faults, which in turn facilitates deep circulation of fluids and geothermal activity. Although faults are known to be the major control on geothermal systems in this region, relatively few fields have been studied in detail. Better characterization of the structural controls on geothermal activity is therefore needed to enhance exploration strategies and reduce the risk of drilling nonproductive wells.
In this project we conduct a detailed structural and 3D geological-geomechanical modeling study of the Astor Pass geothermal field located directly north of Pyramid Lake. The main goals will be to characterize the structural controls on fluid flow and determine the most favorable targets for drilling new wells in this promising geothermal system. We have already conducted extensive geologic mapping and structural analysis in this area, but have yet to develop a comprehensive 3D model or carry out geomechanical analyses of individual fault zones. This project will involve 1) additional detailed geologic mapping of select areas at 1:24,000 scale; 2) more detailed structural analysis of fault zones; 3) compilation of available surface and subsurface data into a 3D structural geological model; and 4) geomechanical analysis of the fractured reservoir by 3D BEM (Boundary Element Method) modeling. Our findings will add to a growing database on the structural controls of geothermal activity in the Great Basin.