Nanopore-Scale Study on CO2–Oil Differential Miscibility, Competitive Adsorption, Cross-Interphase Mass Transfer, and Dynamic Displacement Behaviors

CO₂ miscible flooding has great potential for enhancing tight oil recovery and has become a research hotspot, especially in unconventional reservoir development such as shale oil. Tight reservoirs are mostly dominated by a micronanopore matrix, and the effects of nanoconfinement on CO₂ miscibility cannot be ignored. In this study, we investigated the competitive adsorption, interfacial mass transfer, and dynamic flooding behaviors of the CO₂-oil differential miscible system within nanoporous media using MD simulations and experimental studies. The results show that within nanopores, CO₂ is more likely to be adsorbed by the quartz pore to form an adsorption layer, which strips the C₁₀. As the CO₂ concentration increased to 60 wt %, its stripping ability increased; however, excess CO₂ does not continue to be miscible with C₁₀ molecules but forms a second adsorption layer near the pore surface. This means that the ratio of the number of C₁₀ molecules to the number of mutually soluble CO₂ molecules in the system increased, thereby increasing the minimum miscible pressure (MMP) value of the system. It is worth noting that the CO₂ concentration affects the miscible state, and even if the system reaches the miscible condition, the system will form different degrees of miscible states due to the CO₂ concentration, resulting in different miscible behaviors. In addition, it was also found that with the increase of CO₂ concentration, the MMP value shows a decreasing trend in general, but there is a minimum MMP when the CO₂ concentration is 60 wt %. CO₂ flooding demonstrates a pronounced extraction effect on light crude oil components. Additionally, large-scale CO₂ injection also exhibits an effective extraction capability for heavy components. The research results can provide valuable guidance for the development of tight reservoirs.