Adsorption and Dissolution Behaviors of Carbon Dioxide and n-Dodecane Mixtures in Shale

CO2cyclic injection is a promising method for enhanced shale oil recovery. However, the enhanced shale oil recovery mechanism is unclear, especially the adsorption and dissolution of CO2and oil in kerogen. Therefore, it is of great importance to study the adsorption and dissolution mechanisms of CO2and oil mixtures in shale. In this study, a new experimental apparatus was designed to test the change in the mole fractions of CO2and oil before and after adsorption and dissolution at equilibrium conditions. For simplicity, n-dodecane (n-C12) was used as the oil. The adsorption and dissolution amounts of CO2and n-C12were obtained using a mathematical method. Moreover, the adsorption and dissolution characteristics of the CO2and n-C12mixtures in shale and the effect of pressure on the adsorption and dissolution amounts were studied. Finally, the swelling factor of the shale, which was caused by the dissolution of the mixtures, was calculated from the experimental results. The results show that dissolved n-C12in shale could be replaced by CO2when the mole fraction of CO2in the free phase was larger than a threshold. The adsorption and dissolution amounts of CO2and n-C12increased with pressure. The lower pressure and larger mole fraction of CO2enabled a lower swelling factor of shale. This study provides a straightforward method to experimentally determine the adsorption and dissolution properties of shale, which can be used to evaluate enhanced shale oil recovery by CO2injection and the geological storage of CO2.