Concurrent Monitoring of Hydraulic and Mechanical Properties of Granite Fracture During Hydraulically Induced Shearing in Laboratory

Hydraulic stimulation on the geothermal reservoir is the well-known operation for improving the transmissivity and fracture connectivity within the reservoir. In this operation, by increasing pore pressure, shear slip on pre-existing fractures are triggered or new fractures generate from the tip of pre-existing fractures. Due to these mechanisms, mechanical, hydraulic, and seismic properties of fracture/fracture network evolve during the stimulation, but it is unclear how these properties evolve and link in each other. We conduct the laboratory experiments to concurrently monitor the strength, permeability, and acoustic emissions during the hydraulic shearing of rough-walled fracture. Through the experiments, we find the shear slip is limited to between 0.023% and 0.33% of the representative length of pressurized zone, and the fracture permeability increases to from 4 to 12 times of the initial permeability (before slip). Interestingly, more than 50% of the permeability enhancement is achieved during the aseismic motion, which is commonly precedes the seismic/fast slip with acoustic emissions. These findings are well consistent with the mesoscale experiment at URL and will be useful in the actual operation of pressurization for geothermal reservoirs.