Multiscale Elastic-Waveform Inversion of 2016 Walkway VSP Data from the Raft River Geothermal Field

Abstract

The Raft River geothermal field was selected by the U.S. Department of Energy (DOE) as an Enhanced Geothermal System (EGS) demonstration project in 2010. Vertical seismic profiling (VSP) data were acquired along five walkaway lines at the Raft River geothermal field in 2016 for subsurface imaging, particularly for characterizing the Narrows zone for EGS stimulations. The VSP data were recorded using 84 three-component receivers in well RRG-9. We conduct multiscale elastic-waveform inversion of the VSP data to obtain high-resolution P- and S-wave velocity models for reservoir characterization and migration imaging. We first build a 1D velocity model from sonic log data and zero-offset VSP data, and obtain a 3D traveltime tomography velocity model using the first arrivals of down-going waves in the VSP data. We then conduct multiscale elastic-waveform inversion of rotated and denoised three-component VSP data using the 3D traveltime tomography velocity models as the initial models. Our preliminary inversion result shows a low-velocity zone that may associated with the Narrows zone.