Table 4. Advantages and Disadvantages of Recent Methods in Controlling CO₂ Mobility^{5−7,9,10,12}.

methods	definition	advantages	disadvantages	limitations
CO2 flooding enhanced by nanoparticles	liquids and supercritical CO2 have a viscosity enhancement effect and stabilize CO2 foams due to NPs	decreases the IFT between CO2 and oil	NPs can be harmful to health and the environment due to their small size	high cost of NPs, potentially negative health and environmental impacts, and NP agglomeration (if it occurs)
		improves the viscosity of the CO2 foam	some NPs tend to agglomerate under certain reservoir conditions, which can affect the stability of the injected nanofluids
		certain types of NPs can increase the dispersion of CO2 in aqueous polyacrylamide solutions
control of CO2 mobility with surfactants	in liquid, CO2 can be dispersed through foam formation	surfactants have the ability to prevent the free flow of CO2 by reducing CO2 relative permeability and CO2 flow rate	screening surfactants have a lengthy process	surfactant formulations are prone to instability in harsh reservoir conditions if not properly designed
		eases the impacts of channel separation, viscous fingering, and gravity	possibility of reservoir rock adsorption of surfactants
		reduces IFT and changes wettability
flooding CO2 with polymer-enhanced polymers	formation’s permeability can be reduced by injecting preformed gels or in situ gels	high mobility across the formation	there may be injection problems that affect the size of the area the gel reaches	their use is mainly limited to oil and gas reservoirs with extremely high permeability
		no problems with injection if gelation occurs in the formation	sensitivity of polymer gels to reservoir conditions, which affects gel properties
		if the gel is formed prior to injection, the sensitivity to reservoir conditions is low
CO2 polymers for direct thickening	CO2 has its viscosity increased by direct thickening with polymers	a variety of polymers can dissolve in CO2 to create single-phase and stable solutions; this improves the density and viscosity of CO2 and thereby enhances oil recovery	decrease in the solubility of a polymer with an increase in its molecular weight; moreover, sensitivity influences crystallinity formation, chemical nature of the side-chain moieties, and tacticity	solubility of many polymers requires supercritical conditions