Molecular simulations of adsorption characteristics of clay minerals in shale

The adsorption and desorption characteristics of shale is very important for the development of shale gas. For the sake of thorough understanding the adsorption mechanism in micro-scale view for clay minerals in the shale, three molecular models including illite, montmorillonite and kaolinite were established by using molecular simulation software Material Studio, the grand canonical Monte Carlo(GCMC) method was used for the calculation of isotherm adsorption capacity and adsorption heat. At the same temperature and pressure, isotherm adsorption capacity of CH4 in three clay minerals was in the sequence below: illitemontmorillonitekaolinite. With the increase of pressure, the isotherm adsorption capacity of CH4 in three clay minerals increased, and CH4 adsorption in illite, montmorillonite was more sensitive to pressure changes than that in kaolinite. The heat of adsorption of three clay minerals were less than 42 k J·mol-1, proving that adsorption of CH4 was physical adsorption. With the increase of temperature, the adsorption heat of CH4 reduced and the isotherm adsorption capacity of CH4 was decreased, suggesting that high temperature was disadvantageous to adsorption of CH4.