Exploring the link between permeability and strength evolution during fracture shearing

The evolution of fracture permeability during shearing is crucial in defining the impact of hydraulic stimulation in geothermal and hydrocarbon reservoirs and in describing earthquake mechanisms in induced seismicity. In exploring this phenomenon we link permeability evolution to strength evolution during fracture shearing. In particular, permeability is expected to be incremented by shear-induced dilation for velocity-weakening (i.e., seismic slip) rock fractures and decremented by shearinduced compaction or neutral deformation for velocity-strengthening (i.e., aseismic slip) failure. To confirm our assumptions, a series of experiments are conducted in a triaxial pressure vessel, where confining pressure, pore pressure, and shearing velocity are applied independently, and the evolution of fracture permeability is concurrently monitored. We explore rock rheology through these experiments for both velocity-weakening (e.g., Westerly granite) and velocity-strengthening (e.g., Green River shale) states. The results of comparison study are different from what we expected, but are useful to link between permeability and strength evolution during fracture shearing. This concept will be, furthermore, probed by linking permeability evolution to concepts of dilation and wear recovered from rate-state characterizations of frictional behavior (see Fang et al., 2016 for detail).