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Abstract:
Enhanced geothermal systems are a cornerstone in transitioning from fossil to renewable energy sources. However, applications of its potential are still rare, either due to economic reasons or concerns about induced seismic activity. The large-scale Utah FORGE project (Milford, Utah, USA) with a planned well-doublet reaching a depth of 2.5km in crystalline basement rock addresses both issues. Detailed microseismic monitoring of deep geothermal projects remains challenging and expensive when using additional deep monitoring boreholes. We explore the potential of cost-efficient surface or shallow-borehole (tens of meters) monitoring networks regarding the detection and characterization of injection-induced seismicity during three stimulation stages at Utah FORGE in 2022. The analysis relies on full-waveform-based methods for detecting, locating, and classifying events and inversions for focal mechanisms of the largest events. It also includes exploiting information from a multi-patch geophone nodal deployment via waveform stacking, which helps further lower the surface network's detection threshold. We compare our surface monitoring catalog to the official deep borehole monitoring catalog, which comprises ~2500 events between M -2.09 and 0.52. Preliminary results indicate that despite the higher noise level at the surface and the increased distance to the source area, we can reliably detect events down to M -0.7 using the surface networks. In the ongoing work, we investigate the resolution of seismicity patterns and evaluate the applicability of such cost-efficient surface networks for monitoring geothermal projects.
