Surfactant-polymer flooding formulated with commercial surfactants and enhanced by negative salinity gradient

Abstract

In this study, a high-performance surfactant-polymer (SP) formulation was developed using commercially available surfactants instead of lab-synthesized ones with limited sources. Alcohol propoxysulfates (AES-1 and AES-2), cocamidopropyl hydroxysultaine (CAS), alkyl benzene sulfonate (ABS), and alpha olefin sulfonate (AOS) were mixed in pairs for the formulation screening. The AES-1/ABS formulation with a mixing ratio of 6/4 was able to achieve ultralow interfacial tension (IFT) and possessed excellent aqueous stability at additional NaCl concentration greater than 1.25 wt%. Phase behavior tests illustrated that the optimum salinity (1.6 wt%) and salinity range (1.5 ~ 1.8 wt%) for type III microemulsions were nearly unchanged in spite of the water-oil ratio variation as no in situ soap was generated in the absence of alkali. To investigate the effect of different salinity profiles on the post-polymer SP flooding, 3 corefloods were conducted at 0.3 wt% surfactant concentration. Highest incremental oil recovery (34.8% OOIP) by SP flooding was obtained in coreflood No.2 in which 1 PV NaCl preflush, 0.3 PV NaCl-SP slug, and 0.2 PV polymer drive with additional NaCl of 2.0 wt%, 1.6 wt% and 0.5 wt% were successively injected. Reducing preflush volume in coreflood No.1 and No.3 resulted in lower incremental oil recovery. Effluent TDS analysis indicated that only in coreflood No.2 the maximum effluent salinity (22,249 ppm) exceeded optimum salinity (about 21,000 ppm) and negative salinity gradient concept was realized in the whole SP flooding process. With sufficient salinity preflush, the AES-1/ABS formulation achieved a cumulative oil recovery as high as 93.9% OOIP after polymer flooding.