Which is the most efficient candidate for the recovery of confined methane: Water, carbon dioxide or nitrogen?

In this paper, we explored the recovery dynamics of confined methane (CH4) with water (H2O), carbon dioxide (CO2) and nitrogen (N2), by performing molecular dynamics simulations. Through theoretical analysis, we obtained a simple yet effective method to calculate the stress caused by adsorption/desorption. By comparing the adsorption energies and configurations of CH4, H2O, CO2 and N2 on graphene surface, it indicated that CO2 is the best candidate in displacing CH4. The energy barriers of displacing one adsorbed CH4 molecule by CO2, H2O and N2 were found to depend on the displacement angle, and that vertical displacement costs the lowest energy. The energy barriers of displacing one molecule in an adsorbed CH4 layer under different conditions were also obtained. Furthermore, displacement efficiencies of the adsorbed CH4 confined in the carbon nanotube were compared. The displacement efficiency is in the order of CO2>N2>H2O. Our study may help to reveal the underlying mechanisms of adsorption/desorption phenomena, understand the shale gas recovery from the atomic level and provide new idea in shale gas exploitation technology.