Seismic Imaging of Supercritical Geothermal Reservoir Using Full-waveform Inversion Method

Abstract

To examine the imaging capability of the supercritical water reservoirs as one of the future geothermal energies, we conducted simulations using full-waveform inversion (FWI) method. We studied two cases: one for active source, one for nearby natural earthquakes. For the first case, we assumed borehole active seismic source at the 2 km depth combined with seismic arrays at surface, borehole, observation well and horizontal well. The distributed acoustic sensor (DAS) is assumed as the array sensor in the borehole providing extremely dense seismic data. The result of full-waveform inversion showed very precise location, shape and physical properties (Vp, Vs and density) of the reservoir model. For the second case, we examined the use of near-by natural earthquakes as passive seismic sources. This case showed reasonable location, a shape of an igneous intrusion, but physical properties inside of intrusion are not well retrieved probably due to the limited locations of assumed natural earthquakes. In the future field study, we will use both of active and passive sources to obtain better imaging for the supercritical reservoirs. We think that supercritical water zone can be well imaged by the combination of the full-waveform method, active seismic sources and/or appropriated natural earthquakes, and the DAS seismic array(s) in the borehole and surface seismic array.