Dynamic Interfacial Evolution and Miscibility of CO₂-Alkane Systems: The Role of Chain Length

As carbon dioxide (CO₂) injection plays an increasingly important role in greenhouse gas mitigation and enhanced oil recovery (EOR), a fundamental understanding of CO₂-oil interfacial dynamics is essential for optimizing miscibility and displacement efficiency. In this study, molecular dynamics simulations (MD) are employed to systematically investigate interfacial evolution in CO₂-alkane systems, with particular emphasis on the effects of pressure, temperature, and alkane chain length, among which chain length exerts the most pronounced influence on interfacial behavior. Results show that increasing pressure significantly enhances interfacial mass transfer and reduces the density of the alkane bulk phase, whereas increasing temperature promotes CO₂ escape from the oil phase, leading to a corresponding density increase under constant-pressure conditions. Compared with short-chain alkanes, long-chain alkanes exhibit weaker pressure sensitivity and narrower interfacial characteristic lengths, which are primarily attributed to their more ordered molecular structures and tighter packing. These structural features effectively suppress CO₂ dissolution, resulting in lower solubility and reduced oil swelling capacity. The minimum miscibility pressure (MMP) is determined using the vanishing interfacial tension (VIT) method. The results reveal that long-chain alkanes possess lower configurational entropy and higher interfacial stability, which increases resistance to CO₂-oil miscibility and fundamentally accounts for the observed increase in MMP with alkane chain length. Overall, this work provides molecular-level insights into the interfacial evolution and miscibility mechanisms of CO₂-oil systems, offering valuable theoretical guidance for optimizing CO₂ injection pressure and composition-dependent strategies in EOR applications.