CO2 enhanced oil recovery(CO2-EOR)technology not only can improve oil recovery,but also can store the part of CO2 in the geological,which is a"double win"technology.However,due to the large viscosity difference between oil and CO2 and the heterogeneity of oil reservoirs,gas channeling occurs easily during CO2 flooding.It can significantly reduce the oil recovery of CO2 flooding.To solve this problem,the CO2 viscosity can be enhanced by using CO2 thickeners in the CO2 phase,which is the most direct and effective method.In this work,the polymers that used to thicken CO2 at home and abroad were reviewed,including fluorinated polymers,siloxane polymers,hydrocarbon polymers and oxygenated hydrocarbon polymers.By comparing and analyzing the research results and the advantages and disadvantages of existing polymer thickeners,it was found that the hydrocarbon and oxygenated hydrocarbon polymer thickeners are preferred in the research and application for enhanced CO2 viscosity to improve CO2 flooding efficiency.Furthermore,the effective polymer thickeners should have a molecular structure of CO2-philic group and thickening group,atactic polymers,and an average molecular weight of 6 000～15 000.At present,an effective,affordable and environmentally friendly CO2 thickeners has not been found,so the future research studies on CO2 thickeners must focus on designing and synthesizing less expensive,fluoride free,non-toxic,environmentally friendly and highly soluble CO2 thickeners.
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