THE GEOLOGIC CONTROLS OF GEOTHERMAL FLUID FLOW: A 3D ANALYSIS OF THE BRADYS GEOTHERMAL FIELD, NV, USA

Fracture permeability along discrete fault zones provides pathways for geothermal circulation driven by either high crustal heat flow or heat associated with young or active volcanism. Within individual faults, however, fluid flow zones can have variable size, extent, and spatial distribution. The highly variable character of these zones represents a significant challenge to understanding the systematics of geothermal circulation. Here, we present an evaluation of the geologic characteristics that control geothermal fluid flow through detailed 3D analysis of the Bradys geothermal field in the western Great Basin, Nevada. A variety of surface and subsurface data are integrated into a 3D geologic map of the Bradys area. 3D fault geometries, the stratigraphic sequence, and the 3D temperature structure are examined to understand the distribution and extent of geothermal fluid upwelling within the Bradys fault system. These are compared to the location and distribution of production, injection, and unsuccessful wells within the geothermal field, in order to determine which geologic, structural, and temperature characteristics are associated with production and injection geothermal wells. Results indicate that wells crossing a relatively high number of faults in lithologic intervals that are prone to brittle failure and hosting fracture permeability, in addition to wells intersecting faults that are critically stressed with respect to ambient stress conditions, are more likely to be successful than wells crossing fewer faults in favorable lithologic intervals or wells crossing fewer favorably oriented faults.