Geophysical Observations and Integrated Models Over the San Emidio Geothermal Field, Nevada

Abstract

The San Emidio Desert hosts a hidden, forced-convection geothermal resource situated within a prominent right-step of the Lake Range in northwestern Nevada. The site has produced power since 1988, undergoing several phases of development since. Recent exploration drilling 1.5 to 2.5 km to the SW of the current production area has confirmed 162°C fluids 540 m below the surface with favorable permeability for development. This paper presents results from an integrated modeling study of the system that takes advantage of new geophysical data sets, including 211 broadband magnetotelluric stations, 1207 gravity stations, 176 line-km of ground magnetic data and a passive seismic experiment conducted with 1302 stations of 6 geophones each. These data are considered within the context of drilling results and other datasets to develop updated geologic and conceptual models of the geothermal system. Notable results are: (1) imaging of an extensive zone of mineralized/silicified Tertiary sediments along an outflow path and up-dip of normal faulting; (2) imaging of two distinct dome-shaped electrical conductors situated above zones of enhanced temperature and permeability; (3) coincidence of one of these zones with enhanced semblance of passive micro-seismic signals observed using a dense array; and (4) added constraints on the fault block geometry within the right step of the Lake Range, with implications for understanding the controls of deep permeability in the system.