Study on Methane Displacement Law of Coal with Different Metamorphic Degrees by N2 Injection

To reveal the mechanism of gas displacement in coal seam by N₂, the desorption behavior of CH₄ after N₂ injection was studied by using giant canonical ensemble Monte Carlo (GCMC) and molecular dynamics (MD) methods. Through the adsorption and replacement of CH₄ by N₂ on three kinds of coal samples, the influence of different metamorphic coals on the replacement of CH₄ by N₂ was analyzed from the replacement amount and injection ratio. The results show that the average relative concentration of CH₄ in vacuum layer increases after N₂ implantation. The more N₂ injection pressure, the more gas desorption. It can be seen from the two indexes of replacement amount and replacement ratio that CH₄ replacement amount is positively correlated with coal metamorphic degree, while N₂ injection ratio is negatively correlated with coal metamorphic degree. In the same coal, CH₄ replacement amount is positively correlated with pressure, while N₂ injection ratio is negatively correlated with pressure.