Lattice modelling of hydraulic fracture: theoretical validation and interactions with cohesive joints

Abstract A hydro-mechanical coupled lattice-based model for the simulation of crack propagation induced by fluid injection in porous saturated rocks containing cohesive joints is presented. Rock follows an isotropic damage model for tensile fracture and cohesive joints follow a coupled plasticity-damage model. The discretisation uses a dual lattice approach: a Delaunay triangulation for the solid and the boundaries of the associated Voronoi tesselation for the hydraulic part. A classical poromechanical framework for a materials saturated with a single fluid is implemented. First, predictions of crack propagation are compared with analytical models. Then, the interaction between a propagating crack and an existing joint is analysed. Two configurations are considered: the case of a joint that is orthogonal to the crack path and the case of a joint that is inclined by 45 o with respect to the crack path. For the vertical joint, the crack is first arrested because the cohesive joint is weaker than the rock mass. The crack reinitiates at both crack tips and subsequently propagates in one of them. For the inclined joint, the crack follows the joint and therefore its path is deviated. Damage in the rock develops in the back of the crack tip, thereby enhancing the increase of permeability due to damage in the rock mass.