Dissolution Behavior of Multiester Surfactants in CO ₂ Potentially for Carbon Geological Storage: Experimental Measurements and Molecular Dynamics Simulations

CO 2 flooding is a promising method for greenhouse gas emission reduction and enhancing oil recovery rate. Due to the significantly higher production of CO 2 miscible flooding compared to nonmiscible flooding, enhancing the affinity between CO 2 and surfactants is the key to achieving efficient injection into the formation, promoting the formation of miscible flooding, and improving the geological sequestration efficiency of CO 2 . Experimental studies were conducted to investigate the impact of the quantity of CO 2 -philic ester groups and the hydrophobic tail chain length on the dissolution performance in CO 2 . Combined with molecular dynamics simulations, the interactions between each atom of the surfactants and CO 2 atoms were analyzed in depth, and the correlations between the surfactant molecular structures and their CO 2 dissolution performance were established. The microscopic mechanism was revealed at the molecular scale. The results indicate that the solubility of surfactants strongly depends on the quantity of CO 2 -philic groups and the length of the hydrophobic tail chain. CO 2 -philic ester groups can enhance the affinity of surfactants for CO 2 . However, when the number of ester groups exceeds eight or the tail chain length exceeds C 12, their solubility can decrease due to internal spatial effects and conformational limitations. The simulation further reveals that the intermolecular interactions of ester groups with CO 2, along with Lewis acid–Lewis base (LA–LB) interactions, are key factors enhancing the dissolution performance. After adding the multiester surfactants, the uniformity of the mixture of CO 2 and white oil was significantly improved, indicating that this surfactant can effectively promote the mixture of oil and gas, thereby enhancing the oil recovery rate. This study provides an important basis for the optimal design of surfactant structures, which is helpful to realize efficient miscible flooding and promote the development of CO 2 geological storage technology.