Molecular dynamics simulations examined the roles of molecular structure, thermodynamic compatibility, intermolecular association, and mixture composition in the supercritical CO₂ extraction of ten crude oil components at 363.15 K and 15 MPa. Single-component extraction ratios ranged from 80.70% for n-hexane to 5.85% for 2-naphthol. Compounds of similar size differed widely, indicating that topology, aromaticity, and polar functional groups were more informative than molecular size alone. CO₂ solubility parameters obtained from MD agreed with estimates derived from NIST data, and δ_CO2 = 7.28ρ_r captured their reduced density dependence over 303.15–363.15 K. Extraction generally decreased with increasing oil–CO₂ solubility parameter difference. In binary systems evaluated using oil boundaries determined by the half density criterion, higher fractions of nonpolar partners were associated with increased total extraction ratios, whereas higher fractions of polar partners were associated with decreases. Multicomponent systems showed redistribution that depended on the overall composition, and relative diffusion coefficients qualitatively reflected mobility differences. The gas–oil interaction competition factor, R_comp, decreased from 1.985 to 0.087 in the same order as the extraction ratios. Both the thermodynamic and energetic correspondences persisted after excluding 2-naphthol. Configurations and radial distribution functions showed that association in nonpolar hydrocarbons was dominated by dispersion interactions, whereas polar and aromatic components exhibited additional hydrogen bonding, aromatic stacking, and dipolar or electrostatic organization. Local CO₂ enrichment near polar sites alone did not explain overall extraction. Overall, the selective transfer of individual components was consistent with a balance between local CO₂–oil association and collective oil–oil cohesion that depended on mixture composition, while molecular organization may regulate the accessibility of favorable CO₂ contact sites.

As a process fluid in oil reservoirs, carbon dioxide plays a dominant role in enhanced oil recovery by increasing volume and decreasing interfacial tension. To study the volume expansion behavior of a CO₂–oil system under reservoir conditions, ten hydrocarbon components with carbon numbers ranging from 8 to 26 were selected to represent crude oil. Systems of CO₂ with normal alkanes, cycloalkanes, and aromatic hydrocarbons were measured using a self-assembled high-pressure visible cell, with a temperature range of 313.15 K to 353.15 K and a pressure up to 25 MPa. Experimental results demonstrate that pressure and temperature significantly influence the relative volumetric expansion behavior. The expansion rate exhibits a positive correlation with pressure, whereas it shows a negative correlation with temperature. Among different molecular configurations, normal alkanes exhibit the most pronounced swelling effect. This study establishes that the volumetric expansion behavior of crude oil under CO₂ exposure is predominantly governed by n-alkane components with carbon numbers less than 16. In the heavy hydrocarbon (carbon number > 16) and CO₂ system, the influence of hydrocarbon structure and carbon number on the expansion extent is considerably reduced. This paper delivers critical theoretical foundations for elucidating the microscopic interaction mechanisms in CO₂ enhanced oil recovery and optimizing injection parameter strategies.