Displacement Characters of Combination Flooding Systems consisting of Gemini-Nonionic Mixed Surfactant and Hydrophobically Associating Polyacrylamide for Bohai Offshore Oilfield

In this paper, the injectivity and displacement characters of a new polymer-surfactant (SP) flooding system consisting of gemini-nonionic mixed surfactant and hydrophobically associating polyacrylamide (HAPAM) have been studied under Bohai offshore oilfield reservoir conditions. The injectivity tests have shown that the SP system could build higher resistance factor (RF) and residual resistance factor (RRF) to expand sweep efficiency in nonheterogeneous reservoirs. A total of 10 core flooding tests were carried out to investigate the effect of heterogeneity, slug composition, and polymer molecular structure. The results have shown that the system could obtain higher recovery owing to higher viscosity and ultralow interfacial tension (IFT) compare to water flooding and polymer flooding. The slug composition, with 0.175% polymer and 0.3% mixed surfactant, which forms a composite with the ratio of 4:1 gemini surfactant to nonionic surfactant, could allow full play to viscosity and IFT economically. Moreover, we found that the SP system with HAPAM could obtain a higher oil recovery by 6-13% original oil in place (OOIP) than a nonmodified one, as a result of viscoelastic rheology. The laboratory core tests provided credible proofs for large scale application with this SP system in Bohai offshore oilfield.