SES-06. Induced Seismicity in Enhanced Geothermal Systems, and the use of Distributed Acoustic Sensing (DAS) in Seismic Monitoring

Abstract
Enhanced Geothermal Systems (EGS) is a geothermal energy production method that uses hydraulic fracturing in deep, hot, non-permeable rock formations to create a reservoir for extracting geothermal energy. The Utah FORGE (Frontier Observatory for Research in Geothermal Energy) project is exploring EGS to expand geothermal energy production and aims to create a reservoir by testing new technologies. However, EGS has been associated with induced seismicity, wherein fluid injection during operations causes adverse changes in local geologic stress conditions. Studies show that there is a clear causal link, in time and space, between the origin of earthquakes and stimulation injection parameters. The association between EGS and induced earthquakes has been documented worldwide, with varying earthquake magnitudes reported, sparking the need for more stringent monitoring to mitigate the risk of induced seismicity and ensure successful EGS operations. Seismometers and accelerometers are used to monitor EGS injection sites, but high-temperature environments pose challenges due to the use of borehole seismometers. The monitoring of microseismic events can be done using a relatively new technique called Distributed Acoustic Sensing (DAS), which uses fiber-optic cables to record nanometer-level perturbations along its entire length. Our team deployed a 2-km L-shaped surface DAS array at the Utah FORGE site in April 2022 in order to record microseismicity associated with the reservoir stimulation activity. Dense spatial sampling of DAS provides high-resolution seismic data for identifying and locating seismic events, and eventually detect and imaging the propagation of fractures. An overview of induced seismicity on EGS and the challenges faced will be covered. Additionally, DAS data from FORGE was analyzed and preliminary findings on microseismic events detected will be presented. The understanding of EGS and the implementation of DAS could enhance seismic monitoring efforts and the management of injection operations.