Carbon dioxide flooding for enhanced oil recovery: Promise and problems

Of the enhanced oil recovery methods currently being considered for application to many of the nation’s older oil fields, carbon dioxide flooding may offer the largest potential for additional oil recovery. The physical mechanisms by which CO2 contacts and mobilizes crude oil are reviewed. Influence on the displacement process of factors such as the phase behavior of CO2‐crude oil mixtures, swelling of oil by dissolved CO2, and reduction of oil viscosity are considered. Adverse effects of the viscous instability which occurs when very low viscosity CO2 displaces the more viscous oil and water are dicussed. Advantages and disadvantages of three potential methods for controlling the mobility of CO2 are reviewed: thickening CO2 with polymeric additives, reduction of CO2 mobility by high water saturations, and use of surfactants to generate foam‐like emulsions of water and CO2. Field experience to date and the recent surge in field activity are discussed. Finally, a brief assessment of the future of CO2 flooding research and practice is offered.