Microscopic Simulation Of Adsorption And Flow Of Shale Gas In Nanopores

With the rapid development of China's economy,the adjustment of energy structure is imperative.Shale gas,as an important clean energy,has become a technical problem that needs to be resolved urgently.Shale gas as an unconventional natural gas resource.The mineral composition and pore structure of the storage matrix of shale gas is very complex,and it has the characteristics of low porosity and low permeability.Shale pores mainly consist of nanopores less than 50 nm,and the matrix constituents of these nanopores are mainly clay minerals and organic matter.A small portion of shale gas exists in the form of free states in the pores and fractures of shale,and most of the shale gas is adsorbed on the surface of nanopores in organic matter and clay minerals.Therefore,the study of the adsorption and flow laws of shale gas in micro-nanometer pores is of great significance to improve the production of shale gas.In this paper,the adsorption and flow laws of shale gas in clay mineral nanopores are studied by this method.The effects of pressure,pore size,temperature,pore surface structure,pore water content,and salt ions on the adsorption of shale gas are discussed.The effect of driving acceleration,pore size,and pressure on the flow of shale gas in micro-nanopores are also discussed.The research content and results are as follows:First,the adsorption behavior of methane in micro-nanopores was simulated using the Monta Carlo method.The study found that the total adsorption of methane increased gradually with increasing pressure.In the smaller pores,the methane adsorption layer density on the pore surface is higher due to the adsorption superposition by the kaolinite.The change of temperature has a great influence on the methane density of the adsorption layer in the pores,and the total adsorption decreases with increasing temperature.The adsorption of methane on silicon-oxygen surfaces is stronger than that on hydroxyl surfaces.The water content of the pores has a great influence on the adsorption of methane.Increasing water molecules occupy the adsorption sites on the surface of the pores and the density of the methane adsorption layer decreases dramatically.When the water in the pores contains salt ions,the salt ions have no effect on the total amount of methane adsorbed,and only weakly reduce the potential energy of methane in the adsorbed layer.The molecular dynamics method was used to simulate the flow of methane in micronanopores.The study found that the adsorbed methane is still present in the flowing state,but the methane adsorption stability is affected by the methane flow,which reduces the methane density of the adsorbent layer.This phenomenon is related to the slip phenomenon of methane on the pore surface.Methane is non-uniformly distributed on the surface of kaolinite,which proves that strong adsorption sites exist on the pore surface.Under all simulation conditions,the methane on the pore surface has slip phenomenon,and the slip velocity increases with the increase of pressure differentials and pore size,but decreases with the increase of pore pressure.Due to the non-uniformity of methane density in the adsorbed layer,the velocity of methane in the adsorbed layer is also non-uniform.The absolute value of the curvature of the methane velocity-fitting curve increases with the increase of the driving acceleration,which indicates that the z-axis velocity gradient of methane in the pore increases with the driving acceleration.As the pore size increases,the absolute value of the curvature of the velocity-fitting curve decreases gradually,indicating that the velocity gradient along the z-axis gradually decreases.At low pressures,the methane flow profile cannot be described using a parabola,and the flow status of methane on the pore surface changes.