Molecular Dynamics Study On The Influence Of External Electrostatic Field On The Diffusion Of Methane On The Surface Of Kaolinite

Clay minerals are composed of inorganic substances,which play a very important role in the cementation of coal seams,shale layers and tight sandstone layers.There are many components that constitute clay minerals.The components are connected by different shared oxygen to form different layered structures.This structure makes the specific surface area of clay minerals large,and the presence of metal ions enhances the ability of cation exchange,so the ability to host gas is strong,and it is coal-based gas.Therefore,it is of great significance to study the diffusion of methane in clay minerals to strengthen the extraction of coal-measure gas and optimize the energy structure.At present,many achievements have been made in the research on the influence of various influencing factors based on geological conditions on the diffusion of methane in clay minerals and their changing laws.The influence of porosity,pressure and other gases on the diffusion of competitive adsorption with methane,but the diffusion of methane in kaolinite under the action of electric field has not been studied.Thermodynamic and kinetic parameters such as energy are not known.Considering that kaolinite is the main component of unconventional natural gas reservoirs,especially clay minerals in coal-measure strata（coal seam roof and floor）,this paper uses molecular simulation methods to study the effect of different electric field strengths and electric field directions on the effect of CH₄ in coal-measure kaolinite.The surface diffusion is systematically studied.By studying the law of coal-measure gas diffusion in kaolinite-rich rock formations under the action of an electric field,it can further strengthen coal-measure gas extraction and provide a microscopic theoretical basis for parameter optimization.It provides reference for the extraction of gas and tight sandstone gas.The conclusion is:（1）The diffusion rule of CH₄ on the surface of kaolinite under the action of different electric field strengths is obtained.In the process of increasing the electric field,the diffusion coefficient of methane molecules in the Y direction first increased and then decreased.The diffusion coefficient reached the highest at the electric field strength of 10⁷ V/m,which was 51%higher than that when no electric field was applied,and then reached the lowest at 1010 V/m.30%lower than when no electric field is applied.Therefore,in the actual application process,when the electric field strength is 10⁷ V/m,it is beneficial to the enhanced extraction of CBM.（2）The diffusion rule of CH₄ on the surface of kaolinite under the action of different electric field directions is obtained.When no electric field is applied,the diffusion coefficients in different directions are z,y,and x from large to small.When the electric field strength is 10⁷ V/m,the diffusion coefficients in the x,y,and z directions are increased by 6%,51%,and 37.8%,respectively,coMPared with that when no electric field is applied.When the electric field strength is 10¹⁰V/m,the diffusion coefficient in the z direction is the largest,followed by y and x.（3）The diffusion rule of CH₄ on the surface of kaolinite under the action of different electric field strength and pore pressure is obtained.When no electric field is applied,the change law of the diffusion coefficient of CH₄ molecules,that is,with the increase of pore pressure,the diffusion coefficient first decreases,and then gradually increases after reaching the lowest point.When the electric field strength is 10⁷ V/m,the diffusion coefficient of methane molecules first decreases and then increases with the increase of pore pressure.When the electric field strength is 10¹⁰V/m,the diffusion coefficient of methane molecules first decreases,then increases and then decreases with the increase of pore pressure.（4）The diffusion rule of CH₄ on the surface of kaolinite under the action of different electric field directions and pore pressures is obtained.When no electric field is applied,the diffusion coefficients in different directions show a fluctuating trend of both rising and falling.When the electric field strength is 10⁷ V/m and the pore pressure is 5MPa to 10MPa,the z direction is the direction favorable for diffusion,and when the pore pressure is 15MPa to 20MPa,the y direction is the direction favorable for diffusion.When the electric field strength is 10¹⁰V/m and the pore pressure is 5MPa to 10MPa,the y direction is the direction favorable for diffusion,and when the pore pressure is 15MPa to 20MPa,the z direction is the direction favorable for diffusion.