| Abstract |
Tomographic inversions of compressional and shear velocities from field seismic observations at The Geysers have been performed by a number of investigators in an attempt to image important reservoir properties. Anomalies in compressional velocities (V p ), shear velocities (Vs), and the ratio VplVs,have been interpreted to reflect variations in lithology, fracture density, and pore fluid compressibility within the reservoir. Here we critically review those interpretations in the context of physical insight gained from laboratory measurements of velocities on core samples from The Geysers. Systematics between V p and Vs values within the reservoir are Found to be incompatible with a simple interpretation based solely on pore fluid compressibility. With constraints from the laboratory velocity data, a scaling model which incorporates the effects of field-scale compliant features is evaluated and used to extract information concerning fracture properties independently from other effects such as matrix properties. Model fits to field data are used to test hypotheses concerning possible interpretations of field anomalies. Two potential physical models are proposed. |