Fracture Closure in Extension and Stress Dependent Permeability of Jointed Rock

ABSTRACT: Parallel and quasi-parallel joints represent one of the most often observed permeability structures. Frequently, joint sets are closely spaced and although joint mechanical interaction should significantly affect their aperture, the interaction is usually ignored in permeability evaluation. This approach corresponds to the upper limit for rock permeability. By accurately computing the interaction between the joints, we show that modeling a joint set by an infinite array provides the lower limit. Based on conducted computations and physical experiments, we suggest that the internal pressure can, in fact, close the pressurized joints, dramatically reducing rock permeability. Furthermore, the fluid flow through the joint set becomes highly heterogeneous so that the permeability dependence on the joint spacing is not monotonic. Yet, stress dependent permeability, computed more accurately when accounting for joint interaction, is always lower (and often by orders of magnitude) than that based on the assumption of non-interacting joints.