Molecular simulation of N2 and CO2 injection into a coal model containing adsorbed methane at different temperatures

Highlights: • We build the lowest energy coal model containing adsorbed methane. • The desorption behavior of CH4 after the injection of N2 and CO2 was studied. • CO₂ and N₂ are mainly used to drive off methane gas by occupying adsorption sites. • The effect of injecting CO₂ to promote the desorption of CH₄ was better than N₂. To research the dynamic mechanism of nitrogen and carbon dioxide displacement of methane, we used the grand canonical Monte Carlo (GCMC) simulation method to determine the lowest energy coal model containing adsorbed methane. The desorption behavior of CH₄ after the injection of N₂ and CO₂ at different temperatures was studied. Results show that CO₂ and N₂ were mainly used to drive off methane gas by occupying adsorption sites. The total energy of the CH₄-CO₂ model was lower than that of the CH₄-N₂ model. With the increased of temperature, the average relative concentration and motion velocity of CH₄ in the vacuum layer increased. The relationship of the average relative concentration and average velocity distribution of the three gases in the vacuum layer was CH₄>CO₂>N₂. Under the same time conditions, the relationship between the mean square displacement and diffusion coefficient of CH₄, CO₂, and N₂ in different models was CH₄>CO₂>N₂, and they all increased with temperature. The diffusion activation energy of CH₄ in the model injected with CO₂ was reduced by 20.53%, and the effect of injecting CO₂ to promote the desorption of methane was better than that of N₂.