Fracture Permeability Enhancement During Fluid Injection Modulated by Pressurization Rate and Surface Asperities

We present a series of controlled fluid injection experiments in the laboratory on a pre-stressed natural rough fracture with a high initial permeability (& SIM;10-13 m2) in granite using different fluid pressurization rates. Our results show that fluid injection on a fracture with a slight velocity-strengthening frictional behavior exhibits dilatant slow slip in association with a permeability increase up to & SIM;41 times attained at the maximum slip velocity of 0.085 mm/s for the highest-rate injection case. Under these conditions, the slip velocity-dependent change in hydraulic aperture is a dominant process to explain the transient evolution of fracture permeability, which is modulated by fluid pressurization rate and fracture surface asperities. This leads to the conclusion that permeability evolution can be engineered for subsurface geoenergy applications by controlling the fluid pressurization rate on slowly slipping fractures. Understanding the evolution of fracture permeability during hydraulic stimulation of subsurface reservoirs is the key to characterizing fluid transport and formulating strategies to limit induced seismicity. Accordingly, there is a significant interest in deciphering how the fluid pressurization rate, a constitutive operational parameter during injection, influences the transient permeability change during fracture slip. We conducted a series of experiments in the laboratory using different fluid pressurization rates on a natural rough fracture in granite under a pre-stressed state. The fracture had a high initial permeability. Our findings show that when fluid is injected into a fracture with a slight velocity-strengthening frictional behavior, it causes slow slipping with significant permeability enhancement. The change in hydraulic aperture caused by slip velocity is the main reason for the temporary change in permeability, and this effect is modulated by fluid pressurization rate and fracture surface irregularities. Our results suggest that we can modulate the permeability of subsurface geoenergy reservoirs by controlling the fluid pressurization rate on slowly slipping fractures. We conducted fluid injection experiments on a pre-stressed natural rough fracture in granite at different pressurization ratesThe velocity-strengthening fracture exhibits slow slip accompanied by a significant increase in permeability during fluid injectionTransient fracture permeability is controlled by injection-induced slip velocity, modulated by pressurization rate and surface asperities