Study of CH4 and CO2 competitive adsorption on shale in Yibin, Sichuan Province of China

Abstract

Shale gas is an unconventional gas source with substantial development potential. In this study, Longmaxi Formation shale from the Silurian system in Yibin, Sichuan Province was collected for characterizing total organic carbon (TOC), clay mineral content, and other reservoir properties. The pore structure of shale was analyzed by field-emission scanning electron microscopy and low-temperature N2 adsorption–desorption method. Isothermal adsorption experiments for CH4 and CO2 mixtures in shale samples were performed. The second Virial coefficient was used to calculate for the compressibility factor of the gas mixture. The influencing factors of gas adsorption capacity of shale were analyzed. Finally, the CH4 and CO2 adsorption capacities and selection of shale samples were investigated. Under low pressure, the total gas mixture capacity of shale samples was positively correlated with pressure. When the pressure increased to a certain extent, the growth trend of gas mixture adsorption capacity of shale samples decreased. The mixed gas adsorption volume is high at 50 °C for all the proportion. Given the same temperature and pressure, the CO2 adsorption of shale samples is higher than the CH4 adsorption. In competitive adsorption, shale prefers to adsorb CO2. Therefore, CO2 is easier to be adsorbed by shale and this causes CH4 to be released from the adsorption site.