Laboratory observations of permeability enhancement by fluid pressure oscillation of in situ fractured rock

We report on laboratory experiments designed to investigate the influence of pore oscillations on the effective permeability of fractured rock. Berea sandstone were fractured in situ under triaxial stresses of tens of megapascals, and water was forced through the incipient fracture under conditions of steady and pore pressure. We find that short‐term pore pressure oscillations induce ‐term transient increases in effective permeability of the fractured samples. The of the effective permeability enhancements scales with the amplitude pore pressure oscillations, and changes persist well after the stress perturbation. maximum value of effective permeability enhancement is 5 × 10-16 m2 with a permeability of 1 × 10−15 m2; that is, the maximum enhanced permeability 1.5 × 10−15 m2. We evaluate poroelastic effects and show that hydraulic storage does not explain our observations. Effective permeability recovery following oscillations occurs as the inverse square root of time. The recovery indicates that reversible mechanism, such as clogging/unclogging of fractures, as opposed to an one, like microfracturing, is responsible for the transient effective permeability . Our work suggests the feasibility of dynamically controlling the effective of fractured systems. The result has consequences for models of earthquake and permeability enhancement in fault zones due to dynamic shaking from and distant earthquakes.