High-Resolution Subsurface Imaging at Soda Lake Geothermal Field

Abstract

Accurate subsurface velocity models and structural images are of great importance for geothermal reservoir characterization, particularly for fault/fracture detection. However, complex faults/fracture zones in geothermal systems introduce great challenges to reliable estimation of subsurface velocity models and clear imaging of complicated geological structures. We develop a novel multiscale, correlative full-waveform inversion method, and apply the method to 3D seismic data acquired at Soda Lake geothermal site to build a high-resolution 3D velocity model. The inverted velocity model shows some fine geological features with velocity values lower than those of surrounding media. These features may be associated with fault/fracture zones. To obtain a high-resolution subsurface image of Soda Lake geothermal field, we conduct reverse-time migration using 3D compressional-wave and compression-to-shear converted-wave data and the inverted 3D velocity model. Our results demonstrate that 3D full-waveform inversion significantly improves subsurface images of 3D reverse-time migration. We find that the low velocity zones in our velocity inversion results are mostly located along the fault/fracture zones shown in our reverse-time migration images. These high-resolution imaging results could guide the optimal placement of hydrothermal production wells.