Experimental study of fracture response in granite specimens subjected to hydrothermal conditions relevant for enhanced geothermal systems

Sustaining a network of connected fractures is critical to the long-term success of Enhanced Geothermal Systems (EGS). In this study, the effects of coupled Thermal-Hydrological-Mechanical-Chemical (THMC) processes on fracture aperture and permeability were examined by conducting a series of flow-through experiments on artificially-fractured granite specimens at effective stresses of 5 MPa to 36 MPa, rock temperatures of 25 degrees C and 130 degrees C, and injected fluid temperatures of 25 degrees C, 75 degrees C, and 130 degrees C. The higher fracture closure rates observed at higher effective stresses and the incomplete recovery of fracture permeability and hydraulic aperture observed during unloading stages highlight the role of pressure solution. The increase in temperature of the injected fluid increases the recovery percentage of fracture aperture and permeability after unloading.