Characteristic of Adsorption and Diffusion for Methane in Kerogen

In this paper, the adsorption and diffusion characteristics of methane were studied by the Monte Carlo method and the molecular dynamics method in two types of kerogen, including kerogen II-A and kerogen II-D. The effects of temperature, pressure, depth of burial and carbon dioxide on methane adsorption and diffusion were investigated. The results show that the adsorption amount of methane decreases with the increase of temperature. Conversely, it increases with the increase of pressure. The influence of pressure on adsorption amount is greater than that of temperature. With the increase of burial depths, the adsorption amount of methane increase firstly. At the 3∼4 km geological depths, the figure reaches the highest point. Then, the figure experienced a downward trend. At the same time, the diffusion coefficient also shows the same trend as the increase of burial depth. When the carbon dioxide is mixed with methane, the adsorption amount of methane is obviously smaller than that of single component methane, indicating that carbon dioxide will suppress methane adsorption and will also promote the diffusion of methane. This shows that injection carbon dioxide can displace methane to achieve efficient development of shale gas. The results will provide theoretical guidance for macro-exploration and exploitation of shale gas at the molecular level.