Zwitterionic-nonionic compound surfactant system with low chromatographic separation effect for enhanced oil recovery

Abstract

Ultra-low oil/water interfacial tension (IFT) is an important parameter for evaluating the enhanced oil recovery performance of surfactant flooding. It is difficult to achieve ultra-low interfacial tension with crude oil by a single surfactant, so compound system is often used. However, the chromatographic separation effect of each component in the compound system will severely affect the practical oil displacement performance. In this study, a novel compound oil displacement system was prepared by a zwitterionic surfactant (oleic amidopropyl betaine, OAB) and a nonionic surfactant (coconut oil diethanolamide, CDEA) at a mass ratio of 1:1. The capability of reducing IFT, emulsification, wettability reversal and oil film peeling performance of this system were evaluated. The results show that by promoting the dense arrangement of surfactants at the oil/water interface and realizing hydrophilic-lipophilic balance, the OAB-CDEA compound system can reduce the IFT to 10−4 mN/m. The system also exhibits excellent emulsification performance, and when placed at undisturbed state, the small and uniform emulsion droplets demulsify spontaneously and completely within 3 h. The compound system can regulate the wettability of rock surface from oleophilic to strongly hydrophilic, increasing the underwater oil contact angle from 24° to 157°. Based on the static oil film peeling tests, the oil film reduction rate can reach 88%. Using a 0.3% compound system for the core flooding tests, a recovery up to 75% can be attained, which is ∼30% higher than that of simulated formation water flooding. Meanwhile, the system exhibits low chromatographic separation effect, with chromatographic separation factor Foc close to 1. The OAB-CDEA compound system proposed in this work demonstrates excellent oil displacement performance as well as low chromatographic separation effect, exhibiting great potential in oilfield practical application.