A three-dimensional poroelastic analysis of rock failure around a hydraulic fracture

Three-dimensional stress and pore pressure distributions around a hydraulic fracture are numerically calculated to analyze the potential for formation failure resulting from pressurization of the hydraulic fracture. The three-dimensional numerical model used combines the finite element method and the poroelastic displacement discontinuity method. Elements of the model formulation and solution procedures are first presented. Then, the problem of water injection into a rectangular fracture in Barnett Shale is presented and the potential for rock failure is assessed using Mohr-Coulomb failure criterion with a tension cut-off. Simulation results show that rock failure can occur in the vicinity of the fracture especially near the fracture tips. The dominant failure mode is tension in the close vicinity of the fracture where the pore pressure attains its highest values. Shear failure potential exists away from the fracture walls where shear stresses are sufficiently high to overcome the strength of the rock. Analysis for various injection rates shows that the extent of the potential failure zone increases with increasing injection rate. The failure zone is larger when the formation has a higher modulus of elasticity. Injecting a less viscous fluid enhances pore pressure diffusion into the rock and increases the size of the failure zone. (C) 2013 Elsevier B.V. All rights reserved.