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

CO2 cyclic 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 CO2 and oil in kerogen. Therefore, it is of great importance to study the adsorption and dissolution mechanisms of CO2 and oil mixtures in shale. In this study, a new experimental apparatus was designed to test the change in the mole fractions of CO2 and oil before and after adsorption and dissolution at equilibrium conditions. For simplicity, n-dodecane (n-C-12) was used as the oil. The adsorption and dissolution amounts of CO2 and n-C-12 were obtained using a mathematical method. Moreover, the adsorption and dissolution characteristics of the CO2 and n-C-12 mixtures 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-C-12 in shale could be replaced by CO2 when the mole fraction of CO2 in the free phase was larger than a threshold. The adsorption and dissolution amounts of CO2 and n-C-12 increased with pressure. The lower pressure and larger mole fraction of CO2 enabled 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 CO2 injection and the geological storage of CO2.