Numerical investigation on the influence of mesoscopic deformation on contact area and hydraulic aperture to fracture seepage

Abstract Fluid flow through a single fracture is commonly described by the cubic law. However, deviations from this model are expected because natural fracture surfaces are rough and in contact with each other in discrete regions. In this study, the interactions between fracture closure, contact area, and hydraulic characterization of mesoscopic‐scale rough fractures were investigated. First, natural‐splitting fractures induced by Brazilian splitting were generated and digitally reproduced using a three‐dimensional scanner. The distribution characterization of the initial mechanical fracture apertures was described, and the variation in fracture contact area during fracture closure was evaluated. Second, numerical simulations of fluid flow between rough surfaces were conducted, and the Stokes equations were solved. The results reveal that the hydraulic aperture underwent three stages. When the contact area was less than 0.34%, changes in the hydraulic aperture resulted in flow rate changes that were consistent with the cubic law. When the contact area was between 0.34% and 14.41%, the hydraulic aperture gradually deviated from the cubic law and fell below the mean fracture aperture. At this stage, the hydraulic aperture should be fully considered rather than the mean fracture aperture. When the contact area exceeds 14.41%, although the mechanical fracture decreases with increasing strain, the influence of the contact area on the hydraulic aperture gradually diminishes. This is because the fractures contain less fluid, and the hydraulic aperture approaches the minimum. Finally, the relationship between mechanical and hydraulic aperture strains was established, improving geological engineering applications that account for fracture deformation.