Numerical simulation results of multi-stage hydraulic fracturing in a naturally fractured reservoir with explicit representation of a realistic number and geometry of discrete natural fractures is presented. The parametric study considers different strengths and hydrological properties of DFN. The fracture paths obtained at the end of the four zipper stages stimulation are a combination of pre-existing fracture segments as well as new fractures generated in the intact rock. The stimulation responses in the DFN simulation cases are overall quite similar but consistent, with a larger fractured footprint for lower fracture friction and lower fracture cohesion. Comparison of results with and without a DFN show that both the extension of the fractured zone in the direction perpendicular to the minimum principal stress and the fracture evolution pressure are larger in the case without a DFN, as expected.
Although interaction of a hydraulic fracture with a single discontinuity has been studied extensively (experimentally, analytically and numerically), the authors are not aware of a comprehensive study of multi-stage hydraulic fracturing in naturally fractured reservoirs with explicit representation of a realistic number and geometry of natural fractures in a reservoir. In this work, a physics-based numerical tool is used to investigate the effect of a discrete fracture network (DFN) on reservoir stimulation considering different mechanical and hydrological properties of the DFN.
A number of numerical techniques have been developed to simulate hydraulic fracturing based on different methods such as Boundary Element Method (BEM), Finite Element Method (FEM), Extended Finite Element Method (XFEM), Finite Difference Method (FDM), Displacement Discontinuity Method (DDM), Discrete Element Method (DEM) and some hybrid methods. The formulation of some of the methods and example applications are published by Rougier et al. (2011, 2012); Zhao et al. (2015); and Lisjak et al. (2015). An overview of numerical models for modeling of coupled hydro-mechanical process in naturally fractured rock masses is provided by Lei et al. (2017). The numerical method used to conduct analyses presented in this paper is based on DEM implementation using the lattice approach.