Geothermal Reservoir Imaging Using 2016 Walkaway 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. Reliable geothermal reservoir characterization requires high-resolution subsurface imaging. A vertical seismic profile (VSP) survey was conducted along five walkaway lines in 2016. We build a 3D velocity model using 3D elastic-waveform inversion of the five walkaway VSP data. The 3D velocity model reveals a low velocity zone, which may be associated with the Narrows zone, a fractured zone for EGS stimulation. We then apply 3D least-squares elastic reverse-time migration to the five walkaway VSP data and obtain a high-resolution subsurface image, showing detailed subsurface structures surround the Narrows zone. Our results demonstrate that 3D elastic-waveform inversion and 3D least-squares elastic reverse-time migration of walkaway VSP data can produce useful subsurface information for geothermal reservoir imaging and characterization.