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

Abstract

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.