Effect of molecular weight on the properties of water-soluble terpolymers for heavy oil viscosity reduction

Abstract

BackgroundWater-soluble polymers are increasingly attracting the attention of petroleum engineers for their excellent surface activity and viscosity-reducing properties in enhancing heavy oil recovery. However, the actual formation conditions are highly saline, for which we designed and synthesized a new salt-resistant water-soluble viscosity reducer. MethodsHydrophobically associating terpolymers, poly(Acrylamide/ N-vinyl caprolactam/ quaternary ammonium salt alkyl chains) (ANDs), were synthesized by free radical polymerization in an aqueous solution, and we obtained four different molecular weights of polymers by dialysis. Significant findingsThe results showed that the heavy oil viscosity reduction rates (VRR) of all four polymer solutions were above 98.3% under highly mineralized formation water and high-temperature reservoir conditions. Polymer AND-4 could show good salt tolerance at a high salt concentration of 5 × 104 mg/L NaCl and reached the best viscosity reduction rate of 99.07%. In addition, the polymers' thermal stability, hydrophobicity, surface activity, and salt resistance improved with the increasing molecular weight. Meanwhile, the critical micelle concentration (CMC) and the emulsifying performance improved. This study also discussed the mechanism of viscosity reduction by different molecular weight viscosity reducers. Notably, compared with previous heavy oil viscosity reducers, this work provides a new water-soluble polymeric viscosity reducer with high efficiency and salt tolerance. It also facilitates the design and application of functionalized viscosity reducers for enhancing oil recovery.