Carbon Dioxide Thickening Using Poly(Vinyl Acetate) And Amphiphilic Surfactant

Supercritical carbon dioxide?scCO₂?could be used as fracturing fluid to improve oil recovery effectively but the phenomenon of viscous fingering and gas channeling may occur because of the low viscosity of carbon dioxide,so the viscosity should be enhanced.This paper synthesized four-arm poly?vinyl acetate??PVAc?with different molecule by reversible addition fragmentation chain transfer?RAFT?polymerization and?scCO₂?studied the influence of PVAc with different molecule and concentration on the viscosity of carbon dioxide using the high pressure falling ball viscometer,the viscosity of CO₂ increased 31%-55%at the four-arm PVAc concentration of 1.0 wt%and ethanol concentration of 5.0 wt%.Moreover,the viscosity of the emulsions formatted by poly?ethylene glycol?2,6,8-trimethyl-4-nonyl ether?TMN-6?and microemulsions formatted by poly perfluoropolyether?PFPE?were also studied.The results showed that the viscosity of the emulsion was much higher than that of carbon dioxide or water.At the temperature of 25?40?,carbon dioxide pressure of 10?25 MPa and/mH2O/mCO₂ between 2:8-5:5,the viscosity of the CO₂/water emulsion with 0.2-1.5 wt%surfactant added was 3.78?13.20 mPa s.The viscosity of CO₂/water emulsion increased with increasing the TMN-6 concentration,carbon dioxide pressure and mH2O/mCO₂,and decreasing the temperature.In addition,the flow activation energy?Ea*?and flow activation volume?V*?of the emulsion at different surfactant concentrations were correlated,it was shown that the dependence of CO₂/water emulsion viscosity on temperature and pressure was gradually enhanced with increasing surfactant concentration.Compared to emulsion system,the influence of water/CO₂ microemulsion on the improvement of the carbon dioxide viscosity was slightly.