Multiple Porosity Simulation And Multi-Scale Transport Of Shale Gas Reservoir

This paper first systematically studies the hydrocarbon accumulation mechanism and gas transport mechanism of shale reservoirs.Aiming at the characteristic of free gas and adsorbed gas in shale gas reservoirs,based on the collision frequency of gas molecules,a coupled gas transport model considering slip effect,Knudsen diffusion,and surface diffusion of adsorption gas was established.The relative contributions of different transport mechanisms at different pore sizes and different pressure ranges are discussed.The results show that the relative contribution of surface diffusion and Knudsen diffusion decreases with increasing pressure.As the pressure increases,slip flow becomes the main mode of gas transport.When the pore size and formation pressure are large,the slip flow always dominates the gas transport,and the contribution of surface diffusion and Knudsen diffusion can be ignored.Based on the dual-porosity model,a multiple porosity model for shale gas reservoirs with horizontal fracturing was established to describe the flow in matrix,natural fractures,and hydraulic fractures.The MDS platform was used to discrete and solve the proposed model.By building a typical numerical example,a simulation study of hydraulic fracturing shale gas reservoir was conducted to verify the multiple porosity model.The production trend of typical shale gas reservoirs was studied,and the effects of adsorbed gas content,matrix permeability and related parameters of fracturing wells on gas production were discussed.The results show that the matrix permeability and fracture permeability have a great influence on production.Increasing the fracture permeability is the main controlling factor for increasing the production;the influence of the adsorbed gas content is relatively small and mainly occurs in the late stage.The gas production increases with the increase of the length and numbers of fractures.