Mechanism Of Methane Adsorption And Displacement In Shale Organic Nanopores

As the increasing demand for resources and environmental protection,the exploration and development of shale gas resources has become a research hotspot.The main component of shale gas is methane which enhenced in shale reservoir.Because of its low pollution,wide distribution and abundant reserve,it is considered to be a powerful replacing substitute for coal.Faced with rapid energy consumption and severe environmental problems caused by coal burning,China has shown greater pressure in shale gas exploration,but this has contributed to the shift in energy allocation from coal to natural gas.The precise characterization of methane adsorption and displacement plays an important role in estimating gas location and predicting well productivity.In order to understand methane adsorption and displacement at the micronano scale,molecular dynamics simulation techniques are needed to study the microscopic processes and mechanisms of shale gas in gas adsorption and displacement.In this paper,the adsorption of carbon dioxide/methane in graphene slits and the competitive adsorption and displacement processes and mechanisms of the two are studied.The two-phase flow of methane/water is studied by studying the inorganic nanopores of shale.The carbon dioxide in the graphene slit has a stronger adsorption capacity than methane,and the distribution of carbon dioxide in the adsorption layer tends to be parallel to the surface distribution of graphene;the adsorption strength of carbon dioxide is much greater than the adsorption strength of methane;carbon dioxide tends to be more It is distributed directly above the graphene CC bond,and methane tends to be distributed at the top of the graphene ring center;the interaction between carbon dioxide and graphene surface is stronger and has stronger adsorption capacity.The selective adsorption of carbon dioxide on graphene surface is much greater than that of methane.In the diffusion of mixed components,carbon dioxide strips methane at the wall surface,which causes the diffusion ability of methane to be greater than that of carbon dioxide.The free energy becomes negative,indicating that the displacement process is a spontaneous process.The process of carbon dioxide flooding methane can be completed in a short time;there are two molecular replacement mechanisms in the displacement process;the interaction between carbon dioxide and graphene surface increases gradually during the displacement process,while the surface of methane and graphene The interaction gradually decreases.In the water-gas two-phase flow with different system pressures,methane/water will form two structures: water film and water bridge;methane flow is linear with pressure gradient,but the flow of pure component methane is nonlinear with pressure gradient;In the presence of water,the flow of methane satisfies Darcy's law,the flow of pure methane will slip,and the flow does not satisfy Darcy's law;different water structures will affect the flow of water,and the presence of water bridge will increase the flow of water.When the water film is present,the flow rate of water is reduced;due to the exchange between the molecules at the wall and the water bridge molecules,the velocity profile of the water is still parabolic when the water bridge exists.This work is expected to provide some theoretical guidance for carbon dioxide to enhence shale gas recovery and two-phase flow in nanopores.