Enhanced oil recovery through CO2 injection: The role of pentane in improving miscibility of CO2 and oil

Effectively reducing the miscible pressure of CO 2 -oil is a crucial measure to achieve CO 2 miscible flooding. Alkanes have been extensively studied to improve the miscibility of CO 2 and oil, but few studies have elucidated the potential mechanisms and principles of their effects. In this work, the effect of pentane as a typical alkane on the miscibility behavior between CO 2 and oil is clarified. The interfacial tension of CO 2 -oil was measured by the high temperature and high pressure interfacial tension tester. The minimum miscible pressure (MMP) was extrapolated by the vanishing interfacial tension method. Meanwhile, the physical parameters (solubility, density, etc.) of oil and CO 2 were measured by visual PVT instrument. Oil composition analysis and AFM morphological scanning explained the extraction effect of CO 2 on oil. Finally, pentane-enhanced CO 2 flooding recovery was evaluated by physical simulation device. Results indicated that introducing the pentane effectively reduces the interfacial tensions and MMP, achieving an impressive 10.42% MMP reduction. Moreover, the addition of pentane to CO 2 -oil significantly increases the solubility of CO 2 in oil and the volume expansion of oil. CO 2 primarily extracts oil components with carbon numbers below C 10 . As CO 2 enrichment progresses, the concentration of resin and asphaltene increases, proved by a more roughening of the surface deposition morphology. Pentane can improve the solubilization and extraction of oil by CO 2 , and increase the recovery of CO 2 flooding by 19.94 %. This study is expected to facilitate the efficient utilization of CO 2 miscible flooding and provide the theoretical and technical support for its practical implementation in oilfield.