An Enhanced Synergistic Effect on Increasing Sweeping Efficiency in Surfactant-Polymer Flooding

Abstract Surfactant-polymer (SP) flooding has been considered as an important and high-efficient method to displace the residual oil trapped inside formation rock after initial water flooding. Due to the molecular interactions, some SP formulations exhibit a synergistic effect to further enhance their performance in oil displacement. Current study aims at investigating the synergy in chemical flooding using the SP formulations containing different types of surfactants to increase sweeping efficiency and to enhance the oil displacement efficiency. Among the SP flooding formulations comprising a hydrophobically associative polyacrylamide (HAPAM) bearing a positively charged hydrophobic group and three types of surfactants, an extraordinary performance of the HAPAM combined with an anionic surfactant (AN) was obtained comparing the HAPAM solution mixed with a non-ionic surfactant (NI) or a cationic surfactant (CA). A significantly enhanced sweep efficiency was observed during oil displacement which is related to a high solution viscosity resulting from strong interaction between the HAPAM and the AN. At 90°C, 2 g/L polymer and 0.15 g/L surfactant concentrations, viscosity of HAPAM/AN solution was around 40 times greater than that of the HAPAM solution without surfactant and around 20 times higher than viscosity of the HAPAM/NI and HAPAM/CA solutions. Therefore, the highest oil displacement efficiency was obtained with the HAPAM/AN formulation. Micromodel images indicated that most of saturated oil was affected by injection of HAPAM/AN solution and a very clear, perfectly fan-shaped waterfront was observed during oil displacement. Comparatively, the fingering phenomenon was widely observed during water injection, and SP injection using HAPAM/CA and HAPAM/NI solutions, respectively. The micromodel tests of sequential injection of water slug, chemical slug, and water slug again were also conducted, the results indicated that initial water flooding displaced around 50% of saturated oil. Chemical flooding and extended water flooding further increased the oil production by 18-30%. The injected HAPAM/AN solution exhibited the highest effectiveness in oil displacement among all tested chemical flooding formulations.