Numerical Simulation Of Shale Gas Exploitation Based On Crack Group Model

Shale gas is a clean and high-quality fossil energy, has great potential for development. Shale gas is an important goal of the current exploration and development of natural gas industry in our country. At present the study of shale gas developmentr is still in its infancy in our country, so the numerical simulation of shale gas reservoir exploration is very necessary.This paper based on a detailed analysis of reservoir characteristics of shale gas reservoirs, reservoir mechanism and output mechanism, considering the diffusion of gas in shale matrix, water channeling in the shale reservoir and the change of pressure impact on reservoir porosity, established a mathematical model of shale gas exploitation. And discrete the model by finite difference method, established a numerical model for shale gas seepage which can iterative solve.Modeled of shale gas reservoir by COMSOL,achieved the simulation of shale gas exploitation mathematical model. The parameters of artificial crack group effect on the reservoir pressure are analyzed during the mining: Shale gas reservoir pressure decreases with the mining time; During the shale gas mining process, The reservoir pressure decreased with the increase of the fracture half-length; The reservoir pressure decreased with the increase of the crack angle, the rate of decline gradually decreased with the increase of the angle; The reservoir pressure decreased with the increase of the crack spacing, when after the crack spacing reaching 50 m, the reservoir pressure almost no longer decreased with the increase of the crack spacing.Based on the mathematical model of shale gas exploitation and the numerical model for shale gas seepage which can iterative solve, combined with the calculation formula of fracturing horizontal well productivity, composed shale gas production forecasting program with MATLB. Used the program to forecast the shale gas reservoir productivity and the parameters of artificial crack group effect on the productivity are analyzed.This paper also studied the impact of natural fracture on the shale gas reservoir pressure and the productivity: When the natural fracture did not intersect with the artificial crack group, the impact on the reservoir pressure was negligible, when the natural fractures located outside the scope of the artificial crack group, had little effect for the productivity, when natural fractures located in the scope of the group of artificial cracks but did not intersect, had some influence for the productivity; When the natural fracture just intersected with the artificial crack group, the reservoir pressure decreased maximum, while the productivity reached the maximum; When the natural fracture intersected with the artificial crack group, the natural fracture closer to the horizontal well, the reservoir pressure decreased smaller, the productivity was smaller.