[1] A numerical model incorporating experimentally determined fracture surface geometries and fracture permeability is proposed for characterizing aperture structures and fluid flow through rock fractures under confining pressures. The model was applied to artificially created granite tensile fractures with varying shear displacements (0-10 mm) and confining pressures (10-100 MPa). The findings of the study were consistent with those obtained previously, which characterized experimentally determined contact areas and changes in shear stress during the shear process. While the confining pressures considered herein are higher than those of previous studies, experimentally obtained fracture permeability is important for understanding subsurface flow, specifically the fluid flow characteristics in aperture structures under different confining pressures. Development of preferential flow paths is observed in all aperture structures, suggesting that the concept of channeling flow is applicable even under high confining pressures, as well as the existence of 3-D preferential flow paths within the subsurface fracture network.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.