Stanford Geothermal WorkshopFebruary 9-11, 2026

Enhanced Geothermal Systems (EGS) represent a promising renewable energy solution for extracting heat from fractured low-permeability crystalline formations. Economic feasibility of EGS depends on the long-term mechanical and hydraulic stability of induced fractures under high-temperature and high-pressure subsurface conditions. However, the time-dependent evolution of frictional behavior in geothermal reservoir rocks remains poorly understood, particularly under sustained thermal and hydrologic conditions. At elevated temperatures ( greater than 200 °C) and pressures representative of EGS reservoirs, rock-fluid interactions such as mineral dissolution, ion exchange, or secondary mineral precipitation may alter the fracture minerology and morphology. These chemo-mechanical coupled processes may influence frictional strength over time, but this coupling remain unknown at in-situ conditions. In this study, we introduce a experimental framework to investigate the time-dependent frictional response of granite fractures under EGS conditions, with concurrent monitoring of fluid chemistry. We conduct a series of controlled laboratory experiments using cylindrical granite specimens pre-fractured. To mimic fracture flow, we drill inlet and outlet conduits that intersect the fracture plane, allowing continuous high-salinity fluid circulation directly along the fracture surface. The specimens are loaded in a high-temperature triaxial pressure vessel and subjected to in-situ reservoir conditions representative of 3–4 km depth, a confining pressure of 40 MPa, a pore pressure of 30 MPa, and a temperature of 200 °C. To assess frictional evolution, we apply incremental deviatoric stress and monitor displacement, fracture slip, and the corresponding shear stress. Simultaneously, effluent samples are collected regularly and analyzed for ion concentrations, providing insight into ongoing rock-water interactions. These chemical measurements capture potential mineral dissolution or precipitation processes that may influence the mechanical response through asperity alteration, pressure solution, or sealing effects. The mineralogy of the fracture is also monitored before and after the experiments. The results indicate that such precipitation can significantly alter fracture permeability and mechanical response over time. The integrated mechanical and geochemical coupling provides a time-dependent understanding of how fractures respond under realistic geothermal reservoir conditions.

Topic: Enhanced Geothermal Systems