Molecular simulation of CO₂/N₂ injection on CH₄ adsorption and diffusion

As an efficient and clean energy, coalbed methane development and utilization have deep significance in promoting energy conservation and emission reduction, reducing greenhouse gas emissions. Therefore, molecular simulation was utilized to study the influence of N₂/CO₂ on the adsorption and diffusion of methane in coal under different gas injection methods and to elucidate the influence of varying gas injection methods on the efficiency of coalbed methane extraction, which provides a basis for the efficient development of coalbed methane. The results show that the adsorption effect of gases in coal decreases with the increase of temperature and increases with the rise of pressure, and the adsorption performance of the three gases in coal shows the law of CO₂ > CH₄ > N₂. In addition, the injection of CO₂/N₂ had an obvious inhibition effect on CH₄ adsorption, and the inhibition effect of CO₂ was more significant, and the inhibition effect on CH₄ adsorption reached the maximum when the two gases were mixture injected. In terms of diffusion, compared with separate injection, mixed injection of N₂ + CO₂ promotes CH₄ diffusion more effectively, which can be reflected in the relative concentration distribution and velocity distribution. The injection of N₂ helps to increase the porosity of coal, and the injection of CO₂ and N₂ + CO₂ will lead to the decrease of porosity, but the mixed gas injection has less effect than the injection of CO₂ alone.