Development and Application of AVO Methods and Seismic Attribute Analysis for Characterization of the San Emidio Geothermal Reservoir, Northwestern Nevada

Abstract

Geothermal fields in the Basin and Range province are commonly found in highly faulted and fractured subsurface zones that provide the necessary permeability for vertical fluid flow. This study utilizes a 2D seismic reflection line to explore the geophysical signature of the San Emidio geothermal field’s production zone, located in NW Nevada. An rms-smoothed AVO analysis found low amplitude striations within and adjacent to the reservoir zone, which are coincident to both interpreted faults in our prestack depth migrated seismic image and the subsurface projection of faults mapped in the structural analysis of Rhodes (2011). Rms-smoothed AVO analysis provides new opportunity to utilize pre-stack data in difficult to migrate seismic data sets. Laterally homogeneous 2-layer AVO modeling results at San Emidio indicate that where faulting and fractures are present, pre-critical reflection amplitudes will be reduced by ~66-75% and the critical angle will be increased by ~50%. Far-offset and post-critical offset AVO modeling results are not consistent with empirical observations and potential causes are discussed. Preliminary results of a seismic attribute analysis derived from P- and S-wave velocity models identified a subvertical region of high Poisson’s ratio, associated with brine saturated low-aspect-ratio fractured rock, in the vicinity of the production wells that may show evidence of a geophysical geothermal signature.