Development and application of dilute surfactant–polymer flooding system for Shengli oilfield

A dilute surfactant–polymer (S–P) flooding system has been designed and developed for Gudong oilfield with Shengli petroleum sulfonate (SLPS) as the primary ingredient. The dynamic behavior of the system and the interactions of the system components have been investigated through various methods, including DPD molecular modeling technology and dynamic interfacial-tension analysis. The results have shown a significant synergistic effect between sulfonate and nonionic surfactant. The interfacial tension (IFT) and its time to reach equilibrium could be dramatically decreased, suggesting a fast diffusion–adsorption characteristic of ionic surfactants as well as the high surface activity of nonionic surfactants. P flooding formulation was finalized as 0.3% (w/w) SLPS + 0.1% (w/w) 1# + 0.15% polyacrylamide (PAM), in which 1#, the secondary surfactant, is able to enhance the interfacial activity of SLPS and the flooding efficiency of the system. The S–P flooding system manifests a wide range of IFT with the lowest value of 2.95 × 10− 3 mN/m. The pilot field trial of the system has exhibited outstanding performance to improve oil production and reduce water cut since the first injection of the main slug of the S–P flooding system started in June 2004. Until July 2008, the accumulated oil-production had risen by 17.8 × 104 tons, with the oil-recovery increase by 6.4%. The field trial provides useful information for the further large-scale application of the SP system in Shengli oilfield.