Study on the 3D fluid-solid coupling model with multi-pressure system of shale

The study of fluid solid coupling process in fractured shale reservoir, with massive hydraulic and natural fracture networks, during production is a key scientific issue for accurately understanding the production performance of multi-stage fractured wells. In view of the complicated flow mechanism of shale gas flow, multi-scale media and multiple pressure systems of organic matter/matrix pore/natural fractures and discrete artificial fractures are established to accurately describe the gas flow in shale reservoir. The mathematic model considers mechanisms of non-equilibrium desorption and surface diffusion of the adsorbed gas, the viscous flow and Knudsen diffusion of the free gas, and the influence of matrix pore, natural fracture and artificial fracture pressure system on shale deformation. A fully coupled dual effective stress fluid-solid coupling is established, which considers different pressure system respectively. The influence of rock deformation on shale gas flow in the fractured well production is analyzed. It is found that the natural fracture pressure system is the main influence factor that causes stress sensitivity during the shale gas production. The impact of solid deformation on the permeability of matrix pores continuum is smaller than that of Knudsen diffusion. The apparent permeability of matrix pores continuum is still larger than its original permeability, thus there is no stress sensitivity of matrix pore permeability. With the increase of natural fracture density, the effective stress coefficient of natural fracture pressure system increases rapidly, and the stress sensitivity effect during shale gas production process is stronger.