Molecular simulation of methane adsorption behavior on clay minerals in shale

To investigate factors that influence the adsorption behavior of shale gas in clay minerals from a microscopic perspective,the molecular models of smectite,illite and mixed-layer I / S were built using molecular simulation software Materials studio. Grand Canonical Monte Carlo method was used to simulate methane’ s adsorption behavior on clay minerals. The research results found that the adsorption isotherms of methane on three clay minerals are lower than 42 kJ / mol,demonstrating that the adsorption of methane on clay minerals belongs to physical adsorption. The adsorp- tion isotherms of methane also show the same trend,which conform to the characteristics of type I adsorption curve. The fitting accuracy of Langmuir model is high. The adsorption capacity of methane is in the sequence of smectite > mixed-layer illite / smectite>illite. In mixed-layer I / S,interlayer cations are closer to clay layer than methane. The den- sity of methane adsorbed on the side of smectite is higher than that on the illite side,demonstrating that smectite has stronger affinity to methane compared with illite,but the effect of adsorption on density decreases with the increase of pressure. The authors constructed the clay models with the pore sizes of 1 nm,2 nm and 4 nm,respectively. As pore width decreases,the isosteric heat of methane increases,which means that the adsorption becomes stronger,the adsorp- tion capacity of clay minerals increases,but the absolute and saturated adsorption amount decrease with pore size de- clining.