Study On Shale Gas Multi-field Coupled Seepage Model Based On Porous Structure

Shale reservoirs with low porosity and low permeability characteristics require artificial fracturing technology to form artificial fracturing fractures to ensure ideal gas production.As a kind of unconventional important gas resource,shale gas has different microscopic migration rules than conventional gas,including desorption,gas slippage and seepage.Traditional shale media models are mostly based on Euclidean geometry,and do not consider the effect of shale reservoir pore structure characteristics on gas production rate and gas production.In this paper,the fractal geometry model of shale gas is established based on fractal geometry,and the apparent permeability model of inorganic matrix including slippage flow is derived.According to the structural characteristics of natural fractures,combined with fractal geometry and binary tree model,a fractal binary tree permeability model is derived,and its analytical solution is studied,compared with experimental data to analyze the influence of fracture pore structure parameters on the natural permeability of natural fracture network.At the same time,based on the theory of porous elasticity,the simultaneous porosity dynamic model and permeability dynamic model,the fluid-solid coupling mathematical model of shale gas reservoir is established.Using COMSOL multiphysics numerical simulation software to conduct numerical simulation research on the fractal permeability model,the following main conclusions and results were obtained:(1)Analyze the effects of fluid-solid coupling and non-fluid-solid coupling on gas production rate and gas production through numerical simulation calculations.It is found that under the action of in-situ stress,the gas production rate and gas production are greater than the uncoupled model.(2)The tortuosity capillary beam model contains pore analysis fractal dimension and structural parameters.As the fractal dimension of pores increases,the gas production rate and gas production of shale reservoirs decrease;as the fractal dimension of tortuosity increases,the gas production rate and gas production of shale reservoirs decrease;the larger the maximum pore size,the shale reservoirs The gas production rate and gas production of the layer increase;the larger the characteristic length of the unit cell,the smaller the gas production rate and gas production of the shale reservoir.(3)According to the collision characteristics between gas molecules,gas and pores,an apparent permeability model with slip effect is established.The gas production rate of the apparent permeability model and the gas production rate of the intrinsic permeability model are compared with the field measured data.The study found that the gas production calculated using the apparent permeability model with slip effect is higher than the gas production calculated by the inherent permeability model.At the same time,the pore structure parameters have a significant effect on the slip gas production.The larger the pore fractal dimension,the higher the slip gas production;the greater the tortuosity fractal dimension,the smaller the slip gas production;the larger the maximum pore size,the greater the slip gas production;the fractal permeability characterizes the unit body characteristic length The larger,the smaller the slip gas production.(4)The fractal binary tree permeability model derived from the fractal theory contains many structural parameters of the natural fracture network,such as the fractal dimension of the natural fracture length distribution,the maximum pore diameter of micro-fractures,the capillary diameter,etc.,and the capillary length,etc.Poor,binary tree capillary series,binary tree capillary angle.Through analytical analysis,it is found that the greater the bifurcation angle of the binary tree,the lower the natural fracture network permeability;the greater the fracture length fractal dimension,the lower the natural fracture network permeability;the greater the binary tree capillary series,the natural fracture network permeability The lower the difference;the greater the difference in the binary tree capillary diameter ratio,the higher the natural fracture network permeability;the greater the binary tree capillary length equivalent ratio difference,the lower the natural fracture network permeability;the larger the binary tree capillary maximum pore diameter,the natural fracture network penetration The higher the rate.