Synergistic Effects of Nonionic Surfactant and Organic Alkali for Enhanced Oil Recovery: Optimizing Interfacial Tension Reduction, Emulsion Stability, and Corrosion Control under Optimal Salinity Conditions

This study explores the synergistic effects of Tween 80 surfactant combined with monoethanolamine (MEA) and sodium carbonate (Na₂CO₃) alkalis to reduce interfacial tension, alter wettability, and enhance emulsification for improved enhanced oil recovery under optimal salinity conditions. Experimental results reveal that MEA and Na₂CO₃ comparably improve the interfacial tension (IFT) reduction and wettability alteration capabilities of surfactant solutions. However, MEA demonstrates a superior performance in stabilizing oil–water emulsions with smaller droplet sizes and lower corrosion potential. The IFT of crude oil in water was significantly reduced from 29.8 to 0.222 mN/m using Tween 80 at CMC, and further decreased to 0.0075 mN/m with the addition of 0.75 wt % MEA at an optimal salinity of 1.5 wt % NaCl. This pronounced reduction confirms the synergistic effect between the surfactant and organic alkali, providing a favorable balance of hydrophilic and lipophilic interactions at the oil–water interface. Microscopic analysis revealed that the MEA-surfactant system produced emulsion droplets with an average radius of 5.8 μm, significantly smaller than the 10.4 μm droplets observed with Na₂CO₃, contributing to greater emulsion stability. Additionally, MEA was found to exhibit 57.5% lower corrosiveness on mild steel compared with Na₂CO₃, highlighting its operational advantages for long-term field applications. Core flooding experiments revealed that a surfactant-alkali slug containing MEA and Tween 80 at optimal salinity achieved a 32.37% OOIP recovery, surpassing the 29.40% OOIP recovery from a Na₂CO₃ and surfactant slug. The higher viscosity of MEA-based surfactant-stabilized emulsions improves both macroscopic sweep efficiency and displacement efficiency, leading to improved oil recovery. The combination of Tween 80 and MEA optimizes enhanced oil recovery (EOR) efficiency, reduces equipment corrosion, and enhances sustainability, offering a cost-effective, ecofriendly solution for long-term oil recovery operations.