Molecular simulation of shale gas adsorption in organic-matter nanopore

Shale gas is a kind of unconventional oil-gas resource with tremendous potential. For thorough understanding of the methane adsorption and micromechanism in organic-matter nanopores of the shale and better acquaintances of the occurrence form, graphite slit-pores were set up as a representation of organic-matter nanopores by using Material Studio, and the grand canonical Monte Carlo method, molecular mechanics and molecular dynamics were used for the simulation of adsorption and diffusion behaviors in organic-matter pores on CH4 and CO2 at the shale gas common burial depth of 2-4 km in the Upper Yangtze Plate. The results indicated that the adsorptions of CH4 and CO2 were physical and the optimal storage depth was 2 km; The mixed adsorption data showed the rationality of exploit shale gas by injecting CO2 to exchange CH4, and the optimal burial depth was 4 km; The relative density of CH4 and CO2 along the normal direction of the pore inwall showed a trend of symmetric distribution and apparent adsorption stratifications appeared. As a whole, the self-diffusion coefficient of CH4 and CO2 increased with the increase of burial depth, and it's consistent with the reasons for such changes of adsorption amount and adsorption heat.