Molecular insight into the competitive adsorption mechanism of supercritical CO2/Crude oil in shale composite model

With the continuous growth of energy demand in our country, shale oil, as an important unconventional oil and gas resource, is increasingly highlighting its strategic position. As one of the key means of shale oil development, supercritical carbon dioxide (CO 2 ) flooding technology has significant advantages in reducing crude oil viscosity, improving reservoir pore structure and fluid occurrence state. It can effectively enhance oil recovery. The molecular simulation method provides an effective way to reveal the microscopic mechanism of CO 2 flooding. In this paper, based on the molecular dynamics simulation method, a multi-component system model including supercritical CO 2 , organic-inorganic composite wall and crude oil is constructed. The microscopic mechanism of competitive adsorption of supercritical CO 2 in single-component and multi-component oil phase is systematically revealed. The effects of wall type, temperature and CO 2 injection pressure on competitive adsorption behavior are clarified. The results show that the competitive adsorption behaviors of supercritical CO 2 on different components in shale oil are significantly different. In the single component oil system, the competitive adsorption efficiencies of n -hexane, toluene, acetic acid and n -dodecane are 55.17 %, 51.72 %, 44.83 % and 27.59 %, respectively. In the multi-component oil system, the competitive adsorption efficiencies are as follows: n -hexane (66.58%), n -dodecane (47.06%), toluene (49.46%) and acetic acid (78.78%). This indicates that the competitive adsorption efficiency is closely related to the molecular polarity, molecular weight and its position in the adsorption layer. In addition, we also finds that with the increase of temperature, the competitive adsorption efficiency of CO 2 on n -hexane shows a trend of increasing first and then decreasing, and reaches a peak at 10.5 MPa and 383.15 K (50.57 %). The increase of injection pressure significantly improves the competitive adsorption efficiency, and 10.5 MPa is considered to be the minimum miscibility pressure (MMP). This study reveals the competitive adsorption mechanism between supercritical CO 2 and shale oil from the molecular scale, also provides theoretical support for the technical optimization and scheme design of efficient development of shale oil by CO 2 injection.