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The Effect of Chain Length of Oil and Alcohol As Well as Surfactant to Alcohol Ratio on the Solubilization, Phase Behavior and Interfacial Tension of Oil/Brine/Surfactant/Alcohol Phase Behavior and Interfacial Tension of Oil/Brine/Surfactant/Alcohol Systems American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract Economical microemulsion flooding process can be achieved by optimizing the surfactant formulation for an oil reservoir. This optimization involves the tailoring of a surfactant formulation to fit the conditions for a reservoir, namely, the temperature, the salinity and composition of formation water, and the nature of the crude oil. The general method of optimization of surfactant formulations is to investigate the phase behavior and interfacial tension of surfactant systems containing brine, oil, surfactant and cosurfactant. Solubilization of oil and brine by microemulsion phase containing petroleum sulfonate TRS 10–410 and alcohol was determined at room temperature. Interfacial tension between phases was correlated with solubilization phases was correlated with solubilization behavior of surfactant formulations. The effect of the chain length of hydrocarbon oil on the solubilization and interfacial tension behavior of surfactant formulations was investigated at a surfactant concentration of 5 wt.% and isobutanol concentration of 3 wt.%. Effect of chain length and isomeric structure of alcohols on the solubilization and interfacial tension behavior of dodecane vs. surfactant solution containing 5 wt.% TRS 10–410 and 3 wt.% alcohol was investigated and correlated with the solubility of alcohol in brine. Effect of alcohol and surfactant concentrations on the formation and volume of the middle phase was determined. Surfactant to alcohol ratio was changed in the formulation in order to determine the molecular ratio of surfactant to alcohol in the middle phase. The surfactant to alcohol ratio in the middle phase micro-emulsion was determined using high resolution NMR spectroscopy. Interfacial tension was measured as a function of surfactant concentration to find the interfacial tension concentration minima. The minimum interfacial tensions at low and high surfactant concentrations were correlated by changing salinity and hydrocarbon oil chain length in the surfactant formulation. Introduction Microemulsion flooding process has been widely tested in laboratory and has been applied in field tests in recent years for tertiary oil recovery. In this process, a microemulsion containing petroleum sulfonate, alcohol, oil and brine was used as an injection fluid. The interfacial tension between the microemulsion and reservoir oil or brine is as low as 10 dynes/cm or less. Under adequate conditions, the microemulsion slug is miscible with both oil and brine.

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