3D Modeling of Natural Fracture Stimulation Using a Poroelastic Displacement Discontinuity Method with Slip Weakening

摘要

This paper presents the development and an application of a 3D poroelastic model for hydraulic stimulation of natural fractures while considering shear slip and dilation on preexisting fractures using a slip-weakening approach to fracture deformation. The model uses a coupled finite element/boundary element method to solve for stress, fracture displacements, fluid pressure and leak off to the matrix. Fractures are simulated by considering the nonlinearity of deformation in shear directions and linear behavior in normal direction. The linear slip weakening model is used to simulate the loss of frictional resistance to shear and the residual strength of the pre-existing fractures. Pressure-dependent leak-off is considered to help assess the rock response to injection. After theoretical descriptions and presentation of some aspects of model development, examples are presented to highlight the role of fracture deformation during injection with reference to induced micro-seismicity. Simulation of injection into a large fracture show that shear slip induced permeability enhancement and downhole pressure variations. However, there is lag time between the slip event and permeability change. On the other example effect of shear failure of natural fracture on hydraulic fracture studied and showed that how hydraulic stimulation can end up with shear failure on natural fracture.