Novel Ultra-Low IFT Viscoelastic Surfactant for Chemical-Enhanced Oil Recovery in Sandstone Reservoir with Blend of Anionic-Cationic Surfactants

Abstract Viscoelastic surfactant (VES) shows both the advantages of the surfactant to reduce the interfacial tension (IFT) between crude oil and surfactant solution, and the polymer with high viscosity for mobility control. A novel ultra-low IFT VES composed of a blend of anionic-cationic surfactants was presented. The interfacial performance, phase behaviors, rheological behaviors, static adsorption, and core flood were investigated. VES was prepared by mixing unique mixtures of anionic-cationic surfactants. The apparent viscosity and rheology of the VES solution were measured at 55°C by rotary and oscillatory rheometer, respectively. The interfacial tension between the VES solution and the crude oil (26.0°API) was measured by the spinning drop method in salinity of 15,000 mg/L NaCl. The zeta potential was obtained by measuring the electrophoretic mobility and the static adsorption was carried out on 120~200 mesh sand at 55°C. The phase behaviors of the crude oil and the VES solution were investigated after being kept in sealed pipettes at 55°C for 90 days. The apparent viscosity of VES reached 15 mPa∙s at a concentration of 0.5 wt% between salinity of 0-15,000 mg/L NaCl. Wormlike micelles were obviously observed at concentrations of 0.50 wt% and 0.25 wt%. IFT between VES and the crude oil can be reduced to the magnitude of 10-3-10-4 mN/m at concentrations of 0.01-1wt%. A Zeta potential of -26 mV was obtained for the VES solution. The adsorption of VES was about 1.2mg/g sand. Lower phase microemulsions (Winsor I) were obtained with a solubility parameter of 15 at concentrations of 0.1-1.0wt%. Furthermore, the reduction rate of oil viscosity can reach 96% at concentrations of 0.075%-0.3%. Core flood proved that 19.7 OOIP% additional crude oil was obtained beyond water flood. The pilot test results show that the water cut decreases and the oil content increases. The results imply that the novel ultra-low IFT VES surfactant composed of the blend of anionic and cationic surfactants can not only decrease IFT efficiently but also show good viscosity, thereby providing a promising approach for chemical EOR, especially for low-permeability reservoirs, which are difficult for polymer injection and lack of mobility control.