The Research On Shale SRV Fracturing Matrix- Fracture Coupling Steady Seepage Flow Model

The research on seepage flow model of shale gas reservoir is the basis of shale gas reservoir development.The seepage flow channel in shale gas reservoir contains nanometer,micrometer and millimeter fracture.So the seepage flow of shale gas is multi-scale flow,and it is necessary to establish shale gas multi-scale seepage model.In this paper,shale gas seepage flow area in the formation after volume fracturing is divided into three parts: matrix area,fracture network area and hydraulic fracture area.Assuming shale gas in this three parts is all stable seepage flow,shale gas flux and reservoir pressure is equal at the interface of different seepage flow area.The seepage flow mechanics,fractal theory and fluid mechanics are applied to establish the shale gas reservoir volume fracturing matrix-fracture coupling steady seepage model.Considering shale gas spherical flow,establish shale gas productivity model and analyze the sensitivity of the influence factors of the model,which provides scientific guidance and theoretical basis for the development of shale gas reservoir.The conclusions is shown as following:(1)Considering free shale gas slip seepage,transition diffusion and adsorption gas surface diffusion,establish shale gas nanopore apparent permeability calculation model:with the increase of nanopore radius,gas slippage permeability increases,gas surface diffusion permeability decreases and gas transition diffusion permeabilitychanges little.With the increase of nanopore pressure,gas surface diffusion permeability and gas transition diffusion permeability decreases,gas slippage permeability changes little.With the increase of nanopore radius and pressure,gas slip seepage contribution to total permeability increases,gas surface diffusion seepage contribution to total permeability decreases and gas transition diffusion contribution is small and it can be neglected.The gas type has obvious effect on gas permeability.The order of gas permeability in nanopores is propane> methane> ethane.(2)In the case of the same fractured cross-sectional area,the apparent fractal permeability of fractures order from high to low is: tube model,ellipse model,rectangular model and triangular model.The fractal apparent permeability of fracture increases with the fractal dimension of fractures increasing,decreases first then increases with the increase of fracture bifurcation angle,decreases with the increasing of the coefficient of capillary length,increases first and then decreases with the increase of the width and height ratio of the fractures,decreases with the ellipse fracture long axis and short axis length ratio increasing.(3)Shale gasseepage flow area after reservoir volume fracturing is divided as matrix area,micro fracture network area,hydraulic fracture area.Considering the shale gas spherical oriented flow,establish shale gas production model.Shale gas production is affected by formation pressure,bottomhole pressure,permeability of different seepage areas and geometrical shapes.Shale gas production increases with the increasing of formation pressure;decreases with the increase of bottom hole pressure and increases with the increase of formation temperature;obviously increases with matrix permeability increasing;has little change with fracture network permeability and hydraulic fracture permeability increasing;decreases with reservoir supply radius increasing;increases with downhole supply radius increasing;decreases a little with fracture network apparent radius increasing.