Coupled Flow-Normal-Shear Influence on Fracture Permeability: Analysis and Modeling

ABSTRACT: The subsurface rock fractures are inclined to both normal and shear stresses, resulting in a variation in aperture field, further influencing its hydraulic properties. Laboratory flow-normal-shear test suffers from complexity and low efficiency in measuring the hydro-mechanical response of rock fractures. This work introduces an efficient workflow to model the stress-dependent hydraulic response of rock fractures under both normal and shear deformation. The proposed workflow operates sequentially in four steps. First, fracture closure displacement under effective normal stress is computed using Brown-Scholz model. Second, fracture dilation displacement is calculated using Barton-Choubey model. Then, the new 3D rock fractures under normal and shear deformation are constructed by subtracting the fracture closure and dilation displacements from initial 3D topography of the rock fractures. Finally, fluid flow in the newly-constructed 3D fractures is described using full-physics Navier-Stokes equations. The resulting hydraulic properties are back-calculated based on Darcy’s law and Cubic law. We then demonstrate its applicability with experimental results, which shows a quite good match. The proposed workflow offers an efficient approach to characterize the stress-dependent hydraulic response of rock fractures when subjected to both normal and shear deformation, and could be readily implemented to capture coupled flow-mechanical behaviors of fracture networks in fractured reservoirs.