Seismic Mapping of the Subsurface Structure at the Ryepatch Geothermal Reservoir

In 1998 a 3-D surface seismic survey was conducted to explore the structure of the Rye Patch geothermal reservoir (Nevada) to determine if modern seismic techniques could be successfully applied in geothermal environments. Furthermore, it was intended to map the structural features which may control geothermal production in the reservoir. The results suggested the presence of at least one dominant fault responsible for the migration of fluids in the reservoir. In addition to the surface receivers, a 3-component seismometer was deployed in a borehole at a depth of 3900 ft within the basement below the reservoir, which recorded the waves generated by all surface sources. The subject of this report is use this data set to determine the subsurface structure as a function of azimuth. A total or 2005 first arrival travel times were determined out of 2134 possible traces. 2-D ray tracing was performed to simulate wave propagation from the surface sources to the receiver at depth. The ray tracing was based on a 2-D laterally homogeneous velocity model derived from a velocity profile calculated from a VSP recorded in the same well. It was assumed that differences in travel time between the observed and modeled data are caused by structural deviations from a homogeneously layered model as determined by the VSP profile, and thus were mapped into topographic changes at depth. The results suggest an east-west-trending structure (possibly a horst) with boundaries that match the location of faults found in the analysis of the 3-D seismic surface data