Stress dependence of rock fracture permeability: A comprehensive review of laboratory data and implications for hydraulic stimulation

Fracture permeability controls the fluid flow in unconventional geo-energy reservoirs, and achieving an effective and sustainable increase in permeability is a primary objective of hydraulic stimulation treatments. However, the stress dependence of fracture permeability remains insufficiently constrained. In this study, we systematically compiled and re-processed published hydro-mechanical data of tensile, shear, saw-cut, and natural fractures in representative reservoir rocks, including shale, tight sandstone and crystalline rocks, under diverse stress and deformation conditions. We calculated the fracture permeability, synthesized a unified dataset and systematically quantified the permeability variations with Terzaghi effective normal stress using a commonly adopted exponential law characterized by intrinsic permeability (k₀) and normal stress sensitivity (α). The synthesized dataset indicates that shale fractures are associated with low k₀ and moderate α, suggesting the potential importance of proppant use for maintaining fracture permeability in shale oil/gas reservoirs; sandstone fractures possess high k₀ and low α, favoring sustainable stimulation effects; and crystalline rock fractures have intermediate k₀ and high α, requiring proppants for maintaining post-stimulation permeability. Slip events are generally accompanied by increases in both k₀ and α, enhancing permeability but making it more sensitive to pressure changes, whereas cyclic fluid pressure changes generally compact fractures and reduce both parameters. Laboratory-scale data suggests that shear stress tends to decrease fracture permeability due to asperity crushing and clogging, while field-scale evidence implies permeability enhancement of critically stressed fractures through brecciation. Overall, this study provides a systematic synthesis of existing data for interpreting stress-dependent fracture permeability, which may inform stimulation strategies designed to enhance and sustain fluid transport in unconventional geo-energy reservoirs.