Test results from mixtures of anionic-cationic surfactants significantly broaden the application scope for conventional chemical Enhanced Oil Recovery methods; these mixtures produced ultra low Critical Micelle Concentrations (CMC) as well as ultra-low interfacial tension (IFT) and high oil solubilization that promote high oil recovery.

Mixtures of anionic and cationic surfactants with molar excess of anionic surfactant for EOR applications are described herein. Physical chemistry properties, such as surface tension, CMC, surface excess and area per molecule of individual surfactants and their mixtures were measured by Wilhelmy Plate Method. Morphologies of surfactant solutions, both surfactant-polymer (SP) and alkaline-surfactant-polymer (ASP), were studied by Cryo TEM. Phase behaviors were recorded by visual inspection including with crossed polarizers at different surfactant concentrations and different temperatures. Interfacial tensions between normal octane, crude oil and surfactant solution were measured by spinning drop tensiometer method. Properties of interfacial tension, viscosity and thermal stability of surfactant, surfactant-polymer, and alkaline-surfactant-polymer solutions, were also tested. Static adsorption on sandstone was measured at reservoir temperature. IFT was measured before and after multiple contact adsorptions to recognize the influence of adsorption on interfacial properties. Forced displacements were conducted by flooding with water, polymer, SP and ASP. The core flooding experiments were conducted with water made of a simulated formation brine having approximately 5000 ppm TDS, and with a crude oil from a Sinopec reservoir.

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