摘要
The evolution of fracture geometries caused by asperity damage and gouge formation during the shear significantly affect fluid flow in rock fractures. In this research, a cylindrical sandstone sample was fractured by using the Brazilian splitting test. Fluid flow tests and 3D scanning methods were performed on the fractured sample when it was sheared, to examine how shear-induced alteration of fracture geometries affected the permeability. A simplified modeling algorithm was proposed to quantitatively characterize the asperity degradation and gouge accumulation within the fracture during shear, based on which a series of fracture geometries models at different shear stages were established to conduct the N–S (Navier-Stokes) flow simulations, allowing for an analysis of the link between the fracture geometries evolution and the change in flow behavior during shear. Test results show that shear dilation increase the permeability at the early shearing stages but then was offset by the gouge formation at the residual shear stages, leading to the reduce of fracture permeability. The simulated distribution of asperity degradation and gouge distribution, as well as the normalized permeability change in the sheared fracture correlated well with the experimental measurements. Simulation results show that the fracture permeability is affected not only by the fracture aperture but also by the distribution, location and size of contacts evolving during shear. The channeling flow become more dominant as the shear displacement increases; this is largely controlled by the location of contacts that span almost the entire width of the fracture and has the tendency to block the flow paths. The fluid flow transforms from the dispersion at the early shearing stage to the apparent channeling flow along the narrow side of the fracture in the later shearing stages."