Zhang Jichao

Effects of Surfactants on Interfacial Shear Rheological Properties of Polymers for Enhanced Oil Recovery

The effects of surfactants, namely sodium dodecylbenzenesulfonate(SDBS) and hexadecyltrimethylammonium bromide(CTAB), on the interfacial shear rheological properties of partially hydrolyzed polyacrylamide(PHPAM) and hydrophobically modified polyacrylamide(HMPAM) solutions, which are used in oilfields, were studied using a biconical method. The experimental results show that the interfacial shear complex modulus of HMPAM is significantly higher than that of PHPAM, because an interfacial net structure can be formed by HMPAM molecules through hydrophobic interactions. The SDBS and CTAB molecules can form interfacial aggregates with hydrophobic blocks of HMPAM and destroy the interfacial net structure, which results in a significant decrease in the shear modulus with increasing surfactant concentration. At the same time, the properties of the interfacial film change from viscous to elastic. At low SDBS concentrations, the mixed adsorption film formed by PHPAM and a few SDBS molecules has enhanced strength. However, SDBS molecules can displace PHPAM molecules at the interface and weaken the film at higher surfactant concentrations. The cationic surfactant CTAB neutralizes the negative charge on PHPAM, leading to partial curling of the polymer chain, which decreases the film strength. Relaxation measurements confirmed our mechanism involving destruction of the interfacial netstructure of HMPAM by the surfactant.