Simulating hydraulic fracturing using Finite-Discrete Element Method (FDEM): Effects of pre-existing joints and induced seismicity

International audienceThis numerical study investigates near-wellbore behaviour of Hydraulic Fracture (HF) growth using a Finite-Discrete Element Modeling (FDEM) approach. Our results rarely exhibit a simple bi-wing fracture geometry, but are consistent with analytical solutions and exhibit many features that have been documented in the field. In the case of a homogeneous medium, our simulations show that isotropic far-field stresses (Shmax = Shmin) promote the development of complex fractures, whereas anisotropic far-field stresses (Shmax Shmin) promote branching and curving fracture growth in the general direction of Shmax. A set of pre-existing randomly space distributed joints around the well-bore indicate that fractures prefer to initiate at the joints' tips once intersected by a fluid-driven fracture. They also reveal that possible seismic events due to formation deformation are induced because of shear slippage of critically stressed joints. The presence of multiple joints around the wellbore also increases the extent to which fluid-driven fractures can grow for the same injection energy. Introducing single isolated joints that do not intersect the wellbore, usually created by previous fracturing tests, imposes a lateral stress gradient. The presence of such a gradient leads to asymmetric fracture initiation, generally away from the pre-existing joint. The asymmetric fracture growth is deemed to cause a symmetric micro-seismicity around the well-bore, which explains some of the seismic phenomena observed in the fields