Preparation and Solution Properties of Zwitterionic Polyacrylamide for Enhancing Oil Recovery

The viscosity stability of polymer solution is one of the challenges in enhancing oil recovery, and zwitterionic copolymers present excellent viscosity stability and emulsification performance, enabling effective control of the oil/water interface mobility and enhancing oil recovery. Herein, a zwitterionic copolymer (P(AM/AMBS/MAPTAC)) containing sulfonic acid groups and quaternary amine groups was synthesized by segmentation initiation with AM, AMBS and MAPTAC as monomers. The chemical structure of P(AM/AMBS/MAPTAC) was confirmed by FTIR and ¹H NMR. The M_w value of P(AM/AMBS/MAPTAC) was 9.91 × 10⁶ g/mol, and the apparent viscosity of the 2000 mg/L solution was 24.92 mPa·s at 60 °C at a salinity of 5000 mg/L. P(AM/AMBS/MAPTAC) with sulfonic acid groups and quaternary amine groups exhibited outstanding salt tolerance and shear resistance. When the salinity was 10,000 mg/L and the shear rate was 300 s^-1, the apparent viscosity for the P(AM/AMBS/MAPTAC) solution was 23.45 mPa·s and the viscosity reduction rate was 69.23% at 60 °C for 30 d. Moreover, P(AM/AMBS/MAPTAC) exhibited an improved emulsifying property and a greater oil-water interface thickness than HPAM and SPAM due to the synergistic effect of the sulfonic acid and quaternary amine groups in the P(AM/AMBS/MAPTAC) molecule. The polymer flooding and alkali-surfactant-polymer flooding formed by P(AM/AMBS/MAPTAC) had high chemical oil recovery, and the oil displacement efficiency of P(AM/AMBS/MAPTAC) was higher than that of HPAM and SPAM in the polymer flooding and alkali-surfactant-polymer flooding systems.