Geophysical Characterization of the Northwest Geysers, California

Abstract

The Geysers, in northern California, is the world's largest geothermal power producing field. The Northwest Geysers contains some of the hottest temperatures in the geothermal field, reaching 400 C below 3 km depth. To exploit these high temperatures an enhanced geothermal system is being engineered. However, the source and provenance of the heat is not well understood. This project intends to characterize the anomalous heat source with geophysics, namely newly collected gravity, magnetotelluric (MT), and geochemical data, along with existing magnetic, well log, seismic, and geochemical data. In 2017, 40 MT stations were collected in the Northwest Geysers and imaged an extension to the northeast of the felsite in the area of the high temperatures. In 2018, 200 gravity stations were collected to help constrain this feature. Geochemical data has been collected looking at the age of emplacement of the felsite and will help constrain the provenance of the anomalous heat source in the Northwest Geysers. A three-dimensional geophysical model of the Northwest Geysers will be produced to image subsurface structure.