资源环境科技发展态势分析平台

How fluids flow through pressurized fractured rocks is relevant to many engineering applications and geophysical processes including fault rupturing, hydraulic fracturing, induced seismicity, fluid extraction, and contaminant transport. With increasing fluid pressure and concomitantly elevated hydraulic gradient, the permeability of fractured rock is reduced because of inertial losses within the fluid. There is an accompanying flow regime change when this happens. On the other hand, increasing pressure causes fracture dilation which enhances permeability. In this case, the fracture geometry changes. These two competing consequences of increasing pressure had always been studied independently. Here we present an analytical expression for fractured rock permeability where flow regime and medium geometry simultaneously co-evolve. The theory was applied to core and field flow tests. With continuously increasing fluid pressure, the inertial effect on permeability first dominates over that of fracture dilation and this dominance theoretically reverses at Forchheimer number = 1/3.

Plain Language Summary Flow through fractured impermeable rock mainly occurs in fractures. These flows are dictated by fracture permeability. Permeability is usually considered to be a sole and intrinsic property of the fractured rock irrespective of the fluid and hydrodynamic conditions. But this may not be the case in high-pressure scenarios. Elevated pressure gradients typically occur when the rock is pressurized, that is, when pressure is generally high. Under such large gradients, significant inertial losses take place in the fluid, which results in flow regime transition where the fracture appears to be relatively less permeable. At the same time, any further increase in fluid pressure can cause the fracture to dilate. This expansion increases permeability. Although inertial losses and fracture dilation are intertwined under continuously increasing fluid pressure, their concurrent action and collective effects are unknown. Here, we present a pressure-dependent theoretical expression for inertial and viscous permeabilities of fractured rock under situations where both flow regime and medium geometry evolve. The competing mechanism of inertial losses and fracture dilation on the permeability was revealed with linked experimental and theoretical analyses. These results deepen our understanding of fluid flow in fractured rock when they are subject to coupled hydraulic and mechanical geophysical processes.