A surfactant-polymer and macromolecular surfactant compound system for enhancing heavy oil recovery: Synthesis, characterization and mechanism

Chemical flooding has gained significant attention as an economical and effective technique for enhancing heavy oil recovery. Nevertheless, its application in heavy oil production is often hampered by low sweep efficiency and high injection pressure. To address these challenges, a new oil-displacing agent involving a macromolecular surfactant and a surfactant-polymer compound system has been proposed. This study introduces a surfactant-polymer (PAS) synthesized from acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, and N-hexadecyl-N-sulfo acrylamide, along with a macromolecular surfactant (PSS) made from acrylamide, acrylic acid, sodium p-styrene sulfonate, N-hexadecyl-N-sulfo acrylamide, butyl acrylate, methylene-bis-acrylamide, and nano-silica. The structural composition of PAS and PSS was confirmed through ¹H-NMR and FT-IR analyses. Extensive testing was conducted comparing the performance of PAS, PSS, and a PAS-PSS compound system against an association polymer (AP-1) and a conventional polymer (HPAM). The study focused on thickening performance, interfacial activity, viscosity reduction of heavy oil, and core flooding performance. Results revealed that the PAS-PSS combination significantly outperforms both HPAM and AP-1 in terms of reducing heavy oil viscosity and improving interfacial activity. Specifically, a 1500 mg/L PAS-PSS system achieved a 90.83% reduction in heavy oil viscosity, reduced water–oil interfacial tension to 4.64 mN/m, and had an apparent solution viscosity of 6.45 mPa·s. Oil displacement experiments further demonstrated that the PAS-PSS system enhanced heavy oil recovery by 43.33%, markedly higher than the recovery rates for AP-1 (26.63%) and HPAM (16.76%). Additionally, the compounded system exhibited a lower apparent viscosity, leading to reduced injection pressure. Investigations into the mechanism showed that the PAS-PSS system effectively emulsifies heavy oil to lower its viscosity and increases the viscosity of the water phase. This dual action significantly improves both the oil displacement efficiency and sweep efficiency, subsequently enhancing overall heavy oil recovery. In summary, the use of a surfactant-polymer and a macromolecular surfactant complex system offers a promising advancement in chemical flooding techniques for high-viscosity heavy oil extraction, presenting a novel method to bolster heavy oil recovery operations.

Graphical Abstract