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

Capturing carbon dioxide (CO2) 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 CO2 emissions. Injection of CO2 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 CO2 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 CO2 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 CO2 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 CO2 flooding viz. carbonated water injection, near miscible CO2 flooding, water alternating gas (WAG) injection, CO2 huff ‘n’ puff, and CO2 thickening. Finally, CO2-EOR in carbon capture, utilization and storage (CCUS), the environmental aspects, challenges and future outlooks of CO2 miscible flooding are discussed. Therefore, a repository of CO2 miscible EOR is established in this review assisting an enrichment in our current understanding of this topic.