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

• CH4 and CO2 mixture adsorption on shale was investigated.
• Pore size distribution was studied using N2 adsorption.
• Mineral compositions and microstructure effects on adsorption were analyzed.
• Thermodynamics theory was used to analyze competitive adsorption mechanism.

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 the methane sorption by a factor of 4 for these shales. The study also shows that in the adsorption system of 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, our work 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.