Molecular simulations of the effects of CO2 and N2 injection on CH4 adsorption, coal porosity and permeability
Jienan Pan, Fengmei Jiao, Kai Wang, Yunbo Li, Dangyu Song, Quanlin Hou
Abstract
CO2/N2-enhanced coalbed methane recovery is an important means of increasing coalbed methane production, and understanding the competitive adsorption of CO2, CH4 and N2 in coalbeds and its impact on coal properties is important. A structural model for anthracite from Daning-Jixian was constructed based on elemental analyses, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and carbon nuclear magnetic resonance data. The grand canonical Monte Carlo method was used to research the competitive adsorption of multiple gases on coal and changes in the porosity and permeability. These results indicated that with increasing CO2 injection, considerable methane desorption occurred in the coal seams, and the porosity and permeability of the coal decreased. During N2 injection, the adsorption of methane on the coal increased, and the porosity and permeability of the coal increased gradually. However, the desorption rate of CH4 after injection of N2 was much lower than that after injection of CO2. With CO2 and N2 injection, as the molar mass ratio of N2 to CO2 increased, the quantity of CO2 adsorbed decreased, and the total amount of gas adsorbed on the coal decreased, which increased the porosity of the coal. At an the molar mass ratio of N2 to CO2 is 0.6, the desorption rate of CH4 was 70.95%, the porosity and permeability of the coal were high, and considerable CO2 was sequestered to mitigate greenhouse gas emissions and provide economic and environmental benefits. Document Type: Original article Cited as: Pan, J., Jiao, F., Wang, K., Li, Y., Song, D., Hou, Q. Molecular simulations of the effects of CO2 and N2 injection on CH4 adsorption, coal porosity and permeability. Advances in Geo-Energy Research, 2024, 12(3): 205-222. https://doi.org/10.46690/ager.2024.06.05