Numerical study of dynamic fracture aperture during production of pressure-sensitive reservoirs

Abstract

In fractured reservoirs, some dynamic behavior, such as fracture opening or closure and fracture shear dilation, is induced by the variation of pressure and in-situ stress, which is associated with the fracture aperture and conductivity. In this paper, we focus on the dynamic behavior of fractures and various kinds of affecting factors, including in-situ stress, lithology and fluid pressure. A mathematical model for numerical simulation of the fracture dynamic behavior is developed, which consists of a matrix-fracture stress–strain model and a matrix-fracture flow model. The stress–strain model of fractures is derived, which contains two sections of shear dilation: before-peak dilation and after-peak shear dilation. Then a discrete fracture network (DFN) technology is used to depict the shape of fractures in reality and the model is solved by the finite element method to investigate what the range-ability the fracture aperture presents under the influence of the affecting factors. Based on this model, the effects of pressure distribution, lithology, anisotropic in-situ stress and well production proration are investigated and the specific effects by different affecting factors are analyzed. The numerical outcome indicates that the fracture aperture increases as the field pressure rises. The anisotropic in-situ stress and water injection can trigger large shear dilation, which serves as a positive function in fracture opening.