To investigate the applicability of different gas-soluble surfactants in CO2 miscible flooding for tight oil reservoirs and clarify the underlying mechanism of their enhanced oil displacement, this study first employed the cloud point pressure method to determine the solubility of surfactants in supercritical CO2 under reservoir temperature, thereby identifying the pressure threshold for their stable dispersion. Subsequently, a falling-ball viscometer and an interfacial tension meter were utilized to analyze the viscosity reduction effect of surfactants on crude oil and the regulation law of CO2-crude oil interfacial tension under high-temperature and high-pressure conditions. Next, slim-tube displacement experiments were conducted to quantify the capacity of different surfactants to reduce the minimum miscibility pressure (MMP) of the CO2-crude oil system. Finally, core displacement experiments were performed to systematically evaluate the impacts of surfactants on key development performance parameters of CO2 flooding, including oil recovery factor, oil production rate, and gas-oil ratio (GOR). The results demonstrate that surfactants with a higher number of CO2-philic functional groups and a higher degree of alkyl chain branching exhibit superior solubility in CO2, along with more significant effects on crude oil viscosity reduction and interfacial tension reduction, as well as stronger ability to lower MMP. Among the tested surfactants, AT-1, benefiting from the synergistic effect of its diester groups and isobutyl branches, can reduce the MMP to 39.4 MPa. Core displacement experiments indicate that compared with pure CO2 flooding, AT-1-enhanced CO2 flooding increases the oil recovery factor by more than 5 percentage points, while effectively delaying gas channeling and optimizing displacement dynamics. This study provides certain guidance for the further application of CO2 flooding technology in tight oil reservoirs.
Jing et al. (Thu,) studied this question.