Abstract
A finite volume-based arbitrary fracture propagation model is used to simulate fracture growth and geomechanical stresses during hydraulic fracture treatments. Single-phase flow, poroelastic displacement, and in-situ stress tensor equations are coupled within a poroelastic reservoir domain, using a fixed-strain split assumption. The domain is idealized as two-dimensional and plane-strain, with heterogeneous elastic material and fracture toughness properties. Fracture propagation proceeds by failure along finite volume cells in excess of a threshold effective stress. The cohesive zone model (CZM) is used to simulate propagation of non-planar fractures in heterogeneous porous media under uniform, anisotropic stresses. In addition the model computes the stress field and the pore pressure in the rock matrix to account for stress interference effects. This allows us to estimate the simulated micro-seismic signature of the rock during fracturing. Results show that the presence of bedding planes or planes of weakness in the rock can lead to complex fracture trajectories. The growth of multiple, non-intersecting, competing fractures is also simulated. It is shown that the fracture geometry obtained using this model is highly dependent on the pattern of heterogeneity. For homogeneous reservoirs and a high in-situ stress contrast, planar fractures are obtained. As the stress contrast is decreased and the degree of heterogeneity is increased, fracture complexity increases. Results for different kinds and levels of formation heterogeneity; planes-of-weakness such as bedding planes or natural fracture networks, and layers with different mechanical properties are presented. This model allows for first-of-kind simulation of fracture propagation with arbitrary geometry in a poroelastic solid domain, using proven computational finite volume methods (FVM). The effect of fluid backpressure, mechanical stress shadow effects, and formation heterogeneity are accounted for. The importance of critical stresses on fracture path is discussed.
