Rock Anisotropy Promotes Hydraulic Fracture Containment at Depth

Abstract

We report laboratory experiments and numerical simulations demonstrating that the anisotropic characteristics of rocks play a major role in the elongation of hydraulic fractures (HFs) propagating in a plane perpendicular to the rocks' inherent layering (the bedding planes in sedimentary rocks and foliation planes in metamorphic rocks). Transverse anisotropy leads to larger HF extension in the parallel-to-layers/divider direction compared to the perpendicular-to-layers/arrester direction. This directly promotes vertical containment of HFs in most sedimentary basins worldwide even in the absence of any favorable in-situ stress contrasts or other material heterogeneities. More importantly, the ratio of the energy dissipated in fluid viscous flow in the fracture to the energy dissipated in the creation of new surfaces is found to play a critical role on fracture elongation, with fracture-energy dominated HFs being the most elongated while the viscous dominated ones remain more circular. These results open the door to a better engineering and control of HFs containment at depth in view of the competition between material anisotropy (both elastic stiffnesses and fracture toughness anisotropy) and injection parameters (fluid viscosity and rate of injection).