Abstract:

Shale is mainly composed of organic kerogen and inorganic clay minerals, and the adsorption of kerogen and clay minerals on CH4 is the main source of shale adsorbed gas. In order to study the adsorption behavior of CH4, competitive adsorption behavior of CH4-CO2 and the law of CO2 embedding in inorganic clay minerals, using Na-montmorillonite to characterize clay minerals in shale, and using Lammps software to simulate fluid adsorption at different pressures, temperatures and pore sizes based on the grand canonical Monte Carlo method. The results show that with the increase of pressure, the excess adsorption capacity of CH4 increases first and then decreases at each pore size, and reaches a peak value between 11 and 12 MPa. With the increase of temperature, the excess adsorption amount of CH4 decreased gradually at each pore size. With the increase of pore size, the excess adsorption amount of CH4 decreased gradually. At small pore size, CH4 mainly exists in the form of adsorption in Na-montmorillonite, and with the increase of pore size, the adsorption state and the free state of CH4 coexist in Na-montmorillonite, and the action type of Na-montmorillonite on CH4 is physical adsorption. The CO2 displacement efficiency increases with the increase of initial CO2 pressure and pore size. CO2 storage decreases with increasing temperature, increases with increasing injection pressure, and decreases with increasing pore size. The competitive adsorption ratio of CO2 and CH4 decreased with the increase of pressure and increased with the increase of pore size.

Key words: Na-montmorillonite, silt, grand canonical Monte Carlo method; , competitive adsorption, CO2 sequestration