Reservoir Evolution and Stress Changes during Enhanced Geothermal System Development

Understanding reservoir evolution is essential for developing enhanced geothermal systems (EGS). Induced seismicity carries rich information about subsurface stress changes and fracture activation during EGS development. This presentation synthesizes recent studies at Cape Station and Utah FORGE using seismic networks and borehole distributed acoustic sensing (DAS). We examine microearthquake stress drops, image fracture networks through waveform similarity, and compare focal mechanisms across earthquake sizes and monitoring scales. These observations reveal spatially variable fracture orientations and sequential activation during and after stimulation, providing constraints on reservoir heterogeneity and stress evolution. Combining low-frequency DAS with seismic observations further allows us to reconstruct fault deformation and investigate the evolving contributions of seismic and aseismic slip. Together, these complementary approaches help connect individual earthquakes to reservoir-scale processes and improve geophysical monitoring of geothermal development.

Speaker: Nori Nakata, Lawrence Berkeley National Laboratory