Fundamental aspects, mechanisms and emerging possibilities of CO2 miscible flooding in enhanced oil recovery: A review

• CO 2 miscible flooding, an effective and proven technique to improve oil recovery. • Mechanism of oil swelling with lessened IFT, reduced density and enhanced mobility. • Fundamental aspects repository to enhance understanding of miscible CO 2 flooding. • CO 2 -EOR, an effective technology on forefront supporting CCUS. • Challenges, future horizons and environmental aspects of CO 2 flooding. Capturing carbon dioxide (CO 2 ) at its combustion point and thereby storing it in geological sites or its usage for enhancing oil recovery (EOR) through miscible gas flooding technology aims to mitigate atmospheric/anthropogenic CO 2 emissions. Injection of CO 2 possesses an immense potential for production improvement in matured oil reservoirs. Oil recovery is increased by viscous fluid drive, oil phase swelling and oil viscosity reduction. Miscible CO 2 floods diminish interfacial tension (IFT ∼ 0) between gas and oil, and alters the wettability. This review discusses the various technical aspects of oil production enhancement via miscible CO 2 application with identification of the significant research gaps. The mechanisms of first contact and multiple contact miscibility, techniques of minimum miscibility pressure (MMP) determination (experimental, theoretical and numerical), the influence of CO 2 concentration on rock mineralogy and surface roughness with various associated reservoir parametric (pressure, temperature, salinity, etc.), and the mechanisms of oil displacement from laboratory experiments to field applications are discussed elaborately. The review also deals with the new approaches of CO 2 flooding viz. carbonated water injection, near miscible CO 2 flooding, water alternating gas (WAG) injection, CO 2 huff ‘n’ puff, and CO 2 thickening. Finally, CO 2 -EOR in carbon capture, utilization and storage (CCUS), the environmental aspects, challenges and future outlooks of CO 2 miscible flooding are discussed. Therefore, a repository of CO 2 miscible EOR is established in this review assisting an enrichment in our current understanding of this topic.