Adsorption of methane, carbon dioxide and their binary mixtures on Jurassic shale from the Qaidam Basin in China

CO₂-enhanced shale gas recovery, which plays a crucial role in energy resource development, involves the adsorption of binary mixtures of CH₄ and CO₂ on shale. While numerous previous studies have provided useful insight into CH₄/CO₂ sorption characteristics on shale, few studies have been conducted on binary mixtures absorption on shale. To get better understanding in this field, we carried out an experimental study using shale samples from the Qaidam Basin in China to investigate the adsorption mechanism of CH₄ and CO₂ and their binary mixtures on shales and to evaluate the shale CO₂-enhanced gas recovery potential in more details. The results indicate that the CO₂ sorption capacity exceeds that of themethane sorption by a factor of 4 for these shales. The study also shows that in the adsorption systemof the mixtures, CO₂ plays an advantageous role in the competitive adsorption process. The shale exhibits various behaviors of preferential adsorption of CO₂, which can be related to the shale pore structure. Maximum values of isosteric heat of adsorption for CO₂ and CH₄ are found to be 17.7 kJ/mol and 12.6 kJ/mol respectively. In addition, ourwork denoted that the isosteric heat of adsorption for CO₂ on shale samples increases with increasing adsorption capacity. The study suggests that the CO₂-enhanced gas recovery pattern can be feasible for shales in the Qaidam Basin.