Molecular Dynamics Simulation Of Methane Transport Properties In Carbon Nanopores

The transport property of the fluid in nano-scale pore is the basic and scientific problem of shale gas and other compact oil and gas reservoirs development,and porous nano material research and development.Since the gas flow is influenced by the size effect in nano-scale pore,the conventional hydromechanics theory is improper.This thesis,based on molecular dynamics theory and software,simulates the methane's transport process in carbon nano-scale pore to analyze the slip flow and transition flow of methane under supercritical condition;simulates the methane's distribution and diffusion process in the porous media through the graphite porous media model of different wall structures to reveal the microcosmic mechanism of the interaction between methane in nano-scale pore crack and solid wall particle.And finally,the thesis,through constructing the molecular model of I category and ? category kerogen organic matter,simulates the methane's adsorption and diffusion behavior in kerogen matrix unit under different temperatures and calculates the generated adsorption heat and diffusion activation energy.The main contents and conclusions of the thesis are:(1)It can be found from the methane's molecular dynamics models in two carbon nano tubes with different diameters that the opening direction change of carbon nano tube can cause methane and pore wall's potential energy effect change and influence the flow property of methane.In transition flow,the methane's velocity has fiercely fluctuate in vertical direction and its velocity increases with the increase of graphene six-lattice surface area;the methane's average velocity increases with the increase of micro-pore dimension while its transverse velocity's vertical distribution fluctuate relieves.In slip flow,when the pore wall atom without graphene surface,the Maxwell slip flow theoretical value of velocity distribution and trangential momentum's coordination coefficient C =0.6 is more accordant;for the wall atom is composed by the nano-tube rolled by graphene,the Maxwell slip flow theoretical value of velocity distribution and trangential momentum's coordination coefficient?=0.6 is more accordant;For the same wall structure,the slip degree increases with the increase of driving force.With the increase of driving force,the methane velocity at the center place of pore decreases while its quality flow increases gradually.Meanwhile,with the increase of driving force,the increase trend of slip length decreases and the frictional resistance coefficient decreases with the increase of driving force and Reynolds number while the decrease range lowers with the increase of driving force.(2)Through establishing the graphite porous framework with 1-5mm diameter,the distribution patterns and diffusion properties of methane under 280K and 320K temperature are simulated.The research finds the larger the graphene surface area,the better the adsorption,and the more adsorbed methane,the larger the surface area and the longer staying time of methane in pore.The adsorption layer of methane is formed under the coupling effect of temperature and molecule momentum and the temperature's influence on the methane diffusion has no significant relation solid structure's atomic arrangement.(3)Through constructing the molecular model of I category and II category kerogen organic matter,the isothermal adsorption and diffusion process of methane of different temperatures under 20MPa is simulated.The research finds that the adsorption of kerogen to methane decreases with the increase of time-the methane adsorption decreases about 25 percents for per 20K temperature increase and the adsorption rules confirm to the Langmuir isothermal adsorption characteristics.Since the Barneet kerogen is mainly composed by the aromatic connected to benzene ring,its layered structure can better facilitate the methane adsorption.The adsorption of Barneet kerogen to methane is about 3.37 times to Huadian kerogen.The adsorption of methane in kerogen is mainly physical adsorption.for per 40K temperature increase,the diffusion coefficient of methane increases about 2.3 times.