An experimental method to visualize shear-induced channelization of fluid flow in a rough-walled fracture

This study proposes an experimental method to visualize the channelization of fluid flow through a rough-walled fracture during the shear-flow process using a visualization technique. Transparent fracture samples that have the same surface morphology as natural fractures are prepared for testing. The coupled shear-flow test is carried out and the tracer distributions at different shear displacements and times are captured. The results show that as the shear displacement increases, the number of contacts reduces significantly due to the shear-induced dilation, yet the area of each contact increases. The tortuosity coefficient, defined as the tortuous length of the representative flow path to the straight length between the inlet and outlet boundaries, exhibits a decreasing trend with the increment of shear displacement. This indicates that the expanded aperture induced by dilation gives rise to a less tortuous streamline and weakens the effect of surface roughness on the permeability. In the initial stage of shear, the fluid flow bypasses the contacts, forming a large number of small flow channels. At the residual stage of shear, the fluid flow is concentrated in two or three major channels that have relatively large permeability. The proposed experimental method provides a platform that has a promising potential to intuitively investigate the complex rock–fluid interactions within fractures.