Abstract Accurate characterization of fracture geometry and reservoir structure is essential for the successful design and development of Enhanced Geothermal Systems (EGS). Conventional surface seismic imaging often lacks the resolution to delineate hydraulic fractures at depth due to strong attenuation and limited source frequency. This study presents high‐resolution imaging of the Utah FORGE site using Distributed Acoustic Sensing (DAS) recorded microseismic data during the 16A(78)‐32 injection activities. We developed an imaging technique that leverages microseismic events as imaging sources, applies prestack Kirchhoff migration to each individual source, then stacks hundreds of sources to generate a 3D reflectivity volume. The imaging workflow produces a high‐resolution map of the regional granitoid contact and, more importantly, reveals internal structures within the heart of the geothermal reservoir that have not been previously described. By correlating well‐log data and geological evidence, we identify a low‐angle interface located just below and nearly parallel to the granitoid contact. Key findings also reveal two natural fractures near the stimulation zone, visible prior to stimulation, which may accommodate the injected fluid and affect the hydraulic fracturing efficiency. Those internal structures are difficult to observe by typical surface sources since the regional granite‐alluvium interface is strong and not easily penetrated by seismic waves. Time‐lapse imaging of the hydraulic fracture is conducted and integrated with low‐frequency DAS to construct a more comprehensive fracture geometry. In conclusion, the 3D fracture volume produced by DAS microseismic reflection imaging deepens our understanding of geothermal reservoir dynamics, potentially enhancing geothermal characterization and exploitation strategies.
Ma et al. (Thu,) studied this question.