In this paper,we redefine the original gas-water distribution characteristics of the shale reservoir from the perspective of shale gas accumulation.Unlike the widely used solid-gas interface adsorption theory,shale reservoirs belong to a solid-liquid-gas three-phase coupling system.Therefore,the wall-hydrodynamic model was used to analyze the microscopic gas-water occurrence of organic and inorganic pores.The results show that,shale pores are more likely to adsorb water molecules in the same state,and the content of methane in the adsorbed state is very small.The gravitational potential energy of a single sidewall facing water in organic matter is about 1.6 times that of methane,and about 1.5 times that in inorganic matter.It was found that the adsorption capacity of inorganic matter is weak,the adsorption potential of methane is about 78% of organic matter,and the adsorption ability of water molecules is about 62% of organic matter.In addition,we divide the action distance of the adsorbed molecules,and give the maximum value of the gravitational potential energy the action distance rm of the maximum gravitational potential energy and the limit pore diameter Dm.When the pore diameter D < Dm,the adsorbed molecules are subjected to the double action of the two side walls.When the pore diameter D > Dm,as the pore diameter increases,the area not affected by the wall surface will increase rapidly.However,when D > 50 nm,the gas-occurring state is mainly free gas.The solid-liquid-gas three-phase coupling system can well characterize the real gas-water occurrence of shale,and can lay a good foundation for a deep understanding of the shale reservoir adsorption mechanism.
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