Molecular Simulations Of Methane Adsorption By Inorganic Minerals

Shale gas is a very important unconventional oil and gas resource,in which adsorbed shale gas accounts for 20%~80%.The main component of shale gas is methane,and understanding the adsorption and diffusion characteristics of mineral methane is of great significance to the exploitation of shale gas.Taking into account that molecular simulation has many advantages,this paper uses molecular simulation methods to study the adsorption and diffusion laws of shale gas.First of all,this paper establishes a variety of widths of montmorillonite,kaolinite,chlorite,and quartz slit models,and the use of molecular mechanics methods for geometric optimization of the model.Monte Carlo simulations were used to investigate the effects of temperature,pressure,water molecules,and slit width on the adsorption of shale gas;molecular dynamics simulations were used to investigate the occurrence and diffusion of methane in minerals at different concentrations,and water molecules on methane The influence of the occurrence state and diffusion,the occurrence and diffusion of methane in different slit widths,and the occurrence and diffusion of methane in the presence of small molecular organic matter.The study shows that the adsorption of shale gas in montmorillonite,kaolinite,chlorite,and quartz slits is different,and the adsorption of shale gas in these four minerals is physical adsorption.When water molecules and methane are present on the wall of a mineral slit,the water molecules are preferentially adsorbed on the wall surface,forcing the methane to move to the middle of the slit.The presence of water molecules will reduce the amount of methane adsorbed,because the water tends to form hydrogen bonds with the mineral walls.Therefore,the presence of water molecules will not only seize the space for adsorption with methane,but will also capture methane adsorption sites near these four mineral walls.The greater the width of the slit,the more space for adsorption,the greater the amount of methane adsorbed,and the larger the self-diffusion coefficient of methane;Methane forms adsorbed methane near the mineral wall.As the width of the slit continues to increase,the methane force at the wall facing the middle of the slit decreases,so the methane in the middle is free.The wall of the mineral slit tends to adsorb small-molecule organic matter,so that methane is transported to the middle of the slit,so that the force of the wall facing the methane is reduced.