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

Abstract

Carbon dioxide-enhanced oil recovery (CO 2 -EOR) has gained widespread attention in light of the declining conventional oil reserves. Moreover, CO 2 -EOR contributes to the reduction of the global emissions of greenhouse gases through CO 2 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, CO 2 is used in a continuous flooding scheme for EOR. However, continuous CO 2 flooding tends to be problematic due to unfavorable mobility, viscous fingering/channeling and early breakthrough of CO 2 , 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 CO 2 water-alternating-gas (WAG) injection, polymer-assisted CO 2 injection, surfactant-assisted CO 2 mobility control (CO 2 -foam injection), and nanoparticle-assisted CO 2 flooding. Each method addresses, to an extent, one or more of the problems associated with conventional CO 2 flooding. Furthermore, incorporating more than one method can provide better performance in terms of CO 2 mobility control and oil recovery. In comparison with CO 2 -WAG and CO 2 -foam injection methods, the use of polymers and nanoparticles with CO 2 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.