Seismic imaging of structural features and temporal changes in a geothermal reservoir

Summary In this study we present the results of 3D and 4D Vp/Vs-ratio imaging at The Geysers geothermal reservoir, CA, to image the spatio-temporal fluid distribution in the subsurface. The results of our 3D Vp/Vs analysis show a distinct separation of zones saturated with water and steam, which are corroborated by surface observations and the locations of induced micro seismicity. The results of our 4D Vp/Vs analysis delineate regions where continuous water injection has resulted in an increase of fluid saturation, and where the absence of water injection has resulted in an increase of the steam saturation in the reservoir. The time-lapse results are corroborated by the location of water injection wells and by the volume of injected water.