Development, performance evaluation and enhanced oil recovery regulations of a zwitterionic viscoelastic surfactant fracturing-flooding system

A novel viscoelastic surfactant (VES) fracturing-flooding system composed of amphoteric surfactant octadecyl hydroxypropyl sultaine (OCHSB), cationic surfactant octadecyl trimethyl ammonium chloride (OTAC) and p -toluene sodium sulfonate (NaPts) is proposed to greatly enhance oil recovery. The synergistic effects of two surfactants and counterions were explored and the optimal dosage was determined. Rheological tests show that the system has excellent viscoelastic properties and shear resistance. The shear viscosity of the system with the addition of 4.8 wt% is higher than 25 mPa·s at 80 °C and 170 s −1 . Meanwhile, the drag reduction rate of the system can reach more than 70%. In addition, the system breaks the gel thoroughly, has excellent anti-swelling properties, and the damage to the formation is less than 5%. Finally, the enhanced oil recovery regulations of the system were studied through flooding experiment, and its mechanism was analyzed. The enhanced recovery proves that the system has the dual effects of fracturing and flooding.