Carbon dioxide (CO2) in enhanced oil recovery (EOR) has received significant attention due to its potential to increase ultimate recovery from mature conventional oil reserves. CO2-enhanced oil recovery (CO2-EOR) helps to reduce global greenhouse gas emissions by sequestering CO2 in subterranean geological formations. CO2-EOR has been exploited commercially over recent decades to improve recovery from light and medium gravity oil reservoirs in their later stages of development. CO2 tends to be used in either continuous flooding or alternated flooding with water injection. Problems can arise in CO2-flooded heterogeneous reservoirs, due to differential mobility of the fluid phases, causing viscous fingering and early CO2 penetration to develop. This study reviews the advantages and disadvantages of the techniques used for injecting CO2 into subsurface reservoirs and the methods adopted in attempts to control CO2 mobility. Recently developed methods are leading to improvements in CO2-EOR results. In particular, the involvement of nanoparticles combined with surfactants can act to stabilize CO2 foam, making it more effective in the reservoir from an EOR perspective. The potential to improve CO2 flooding techniques and the challenges and uncertainties associated with achieving that objective are addressed.
© 2022 The Authors. Published by American Chemical Society.