Compound Anionic–Nonionic Surfactant System with Excellent Temperature and Salt Resistance for Enhanced Oil Recovery

The development of a temperature- and salt-resistant surfactant system is of great significance in enhanced oil recovery. In this study, two anionic–nonionic surfactants, alkylphenol polyoxyethylene ether carboxylate sodium-10Na (APEC-10Na) and fatty alcohol polyoxyethylene ether carboxylate sodium-9Na (AEC-9Na), were applied to construct a compound surfactant system. When the total concentration was 0.3% and the mass ratio of APEC-10Na to AEC-9Na was 7:3, the compound system could reduce the interfacial tension between oil and water to 8.1 × 10–2 mN·m–1, which could be attributed to the dense arrangement of the surfactant molecules in the interface. The system can resist temperatures up to 110 °C and tolerate a monovalent salt concentration of 18 × 104 mg L–1 and a divalent salt concentration of 8 × 103 mg L–1. The compound surfactant system can modify the rock surface wettability from strong hydrophobicity to strong hydrophilicity, with an underwater–oil contact angle reaching 132.4° for the treated rock surface. The oil film peeling rate of the compound system is 73.4%, which is 29.2% higher than that of the commercial system and 41% higher than that of the formation water. The oil recovery rate of the compound system in core displacement experiments is 61.7%, which is 4.8% higher than that of the commercial system and 14% higher than that of the formation water. The compound surfactant system proposed in this work not only achieved low interfacial tension under high-temperature and high-salinity conditions but also realized effective interface wettability regulation, sufficient stripping of adhered oil films, and promotion of oil droplet migration, providing guidance in designing compound surfactant system for the efficient development of high-temperature and high-salinity reservoirs.