Hydraulic Fracture Propagation in Pre-structured Media: Stress Field and Fracture Network Topology

Reservoir stimulation by hydraulic fracturing involves intricate hydro-mechanical interactions with preexisting formation features. This study investigates the coupling between the state of stress and the preexisting fracture network topology during hydraulic fracture propagation. We run laboratory experiments with a large triaxial frame and conduct complementary numerical simulations to gain block-scale insights. Silicone imprints reveal a global ellipsoidal geometry with marked three-dimensional branching and preferential flow along fracture intersections. Fracture network topology and the state of stress collude to control fluid invasion and fracture propagation. In isotropic fabrics, the ellipsoidal fracture pattern aligns normal to the minimum stress. However, pronounced fracture network anisotropy may prevail, and wing fractures open instead of a single planar fracture. Extensive dilational distortion of the rock mass develops ahead of the fluid-invaded fractures; low bending stiffness increases the block compliance and hinders the dilational distortion in high stress regimes. Preferential flow along fracture intersections results from block breakage at corners, kinematic block rotation and diminished drag at intersections. The interaction between the invading fluid and gouge induces fluid pressure buildup, gouge displacement and fingered invasion along fracture planes.