Synthesis Of CO₂ Thickener And Its Application On Oil Displacement In Visualized Microchannel

With the development of the economy,the consumption of crude oil is increasing day by day,and the traditional oil displacement technology can no longer meet the needs of extraction.CO₂ flooding technology can effectively improve recovery ratio by extracting light hydrocarbon components in the crude oil,expanding the volume of the crude oil,and decreasing the viscosity,which attracts more and more people in recent years.However,viscosity fingering,breakthrough of gas and premature breakthroughs often appear due to the low viscosity of CO₂.Therefore,using a thickener to increase the viscosity of CO₂ is an effective method to improve the efficiency of CO₂ flooding.In this article,five kinds of CO₂ thickeners P（NNFA-co-St）with different compositions were synthesized by free radical polymerization,where fluorinated acrylate was used as CO₂-proximal segment and styrene was used as CO₂-phobic segment.The structure and molecular weight of CO₂ thickener were characterized by NMR and GPC.The cloud point pressure test and relative viscosity test were used to evaluate the dissolution and thickening properties of the thickener in high-pressure CO₂,and we selected one thickener-CO₂ solution with the best performance as the displacement phase to displace the simulated oil in visualized channels.The influence of CO₂ viscosity on the displacement effect was studied by adjusting the viscosity of the displacement phase through controlling the mass concentration of the thickener,and compared with the similar viscosity C/W emulsion.We found that the optimum molar ratio value for St in co-polymer for the viscosity enhancement of CO₂ was 0.285,and the PNNFA0.715-co-St0.285 was able to enhance the viscosity of CO₂ by 233 times at 5 wt%.The recovery of the thickener-CO₂ solution displacement was significantly higher than CO₂ displacement,and the viscous fingering was significantly improved.Meanwhile,the simulated oil in the branch can be displaced which made the sweep efficiency higher.The recovery efficiency of 5wt%thickener-CO₂ solution can reach 80%,and its sweep efficiency can reach 99%.Compared with C/W emulsion displacement,thickened CO₂ has a more stable displacement efficiency.It provides a theoretical basis for the design of thickeners in practical applications and provides guidance for the application of CO₂ thickener in industry.