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.