Diversity of channeling flow in heterogeneous aperture distribution inferred from integrated experimental-numerical analysis on flow through shear fracture in granite

Shear (Mode II) fractures with shear displacements of 1 and 5 mm were generated by direct shear on granite under normal stresses of 1, 20, and 60 MPa. Fracture surface mapping showed that the surface roughnesses of the shear fractures decreased with increasing shear displacement and normal stress and were smaller than those of tensile fractures reported in our previous study. Fluid flow experiments on the shear fractures provided fracture permeabilities at a wide range of confining pressures of 10–100 MPa. Nonmonotonic permeability was usually observed to decrease with increasing confining pressure. However, the permeability changes were different between the shear fractures generated at the normal stress of ≤20 and 60 MPa. In addition, obvious permeability changes with shear displacement were observed for 60 MPa, whereas no significant difference was observed for ≤20 MPa. Comparing the shear fractures with the tensile fractures having shear displacements revealed clear differences, even for equivalent shear displacements. Numerical models that were constructed using the data of the fracture surface mapping by matching their permeabilities with the experimentally evaluated fracture permeabilities revealed the development of preferential flow paths, i.e., channeling flows, for the shear fractures, providing a diversity of channeling flow in heterogeneous aperture distributions of rock fractures in the Earth's crust.