Investigation of Shale Gas Numerical Simulation with Fracture Stress-Sensitive Using Discrete Fracture Network Model

Abstract

Abstract The exploitation of unconventional reservoirs is increasingly a major source of long-term energy in the word. Research results have revealed that the natural fractures occur in shale gas reservoirs and many shale outcrops, cores, and image logs contain fractures or fracture traces, and microseismic event patterns associated with the hydraulic fracture stimulation have been ascribed to the natural fractures reactivation. Hydraulic fracture treatments also induce complex fracture geometries in naturally fractured shale gas reservoirs. The production performance of shale gas plays denpend strongly on the existence of a dense and conductive network volume of the well. Most of shale gas reservoirs exhibit a higher degree of heterogeneity and complexity created by both natural and hydraulic fractures, whose permeability is stress-dependent. In order to describe the fracturs's seepage characterization explicity, the discrete fracture network (DFN) model is adopted in this research when the conventional continuum model cannot meet the requirements of the fractured shale gas reservoirs numerical simulation. The nonlinear partial differential equations about the seepage flow mathematic model are solved by finite volume method using the C-sharp programming language. The fracture permeability stress-dependent experiments have been conducted on shale core samples, and then the fracture aperture-pressure correlation is combined with the mathematic model of DFN to demonstrate the fracture conductivity potential impact as pressure drops during production. The lab experiment results show that the fracture aperture is strong stress-sensitive at low pressure (0~20MPa). The model is used to do a simulation on a random generated fractures network, which is used to represent the fractured shale gas reservoir, to study the effect of the stress-sensitive on the flow and transport characteristics in the fractured porous media. Results show that: the fracture permeability stress-sensitive has a significant impact on the production and should not be ignored.