A review of recent developments in CO2 mobility control in enhanced oil recovery

Carbon dioxide-enhanced oil recovery (CO2-EOR) has gained widespread attention in light of the declining conventional oil reserves. Moreover, CO2-EOR contributes to the reduction of the global emissions of greenhouse gases through CO2 sequestration in subsurface geologic formations. This method has been largely used in the petroleum industry for several decades especially for extracting oil from light-to-medium oil reservoirs approaching an advanced state of maturity. Traditionally, CO2 is used in a continuous flooding scheme for EOR. However, continuous CO2 flooding tends to be problematic due to unfavorable mobility, viscous fingering/channeling and early breakthrough of CO2, especially in the presence of reservoir heterogeneities. In this paper, recent developments in the methods used to overcome these problems are reviewed. These developments include CO2water-alternating-gas (WAG) injection, polymer-assisted CO2 injection, surfactant-assisted CO2 mobility control (CO2-foam injection), and nanoparticle-assisted CO2 flooding. Each method addresses, to an extent, one or more of the problems associated with conventional CO2 flooding. Furthermore, incorporating more than one method can provide better performance in terms of CO2 mobility control and oil recovery. In comparison with CO2-WAG and CO2-foam injection methods, the use of polymers and nanoparticles with CO2 flooding is relatively new. These two new methods were mostly investigated experimentally, at the laboratory level, and they still need further development prior to field implementation.