The objective was to identify surfactants for Enhanced Oil Recovery by brine-oil interfacial tension reduction for a carbonate reservoir at ~ 25°C and salinity of ~11,000ppm TDS; thus, Alkyl Propoxy Sulfates and their blends with sulfonates were evaluated to determine optimal salinity and solubilization parameters with dead crude. Imbibition experiments were performed in reservoir and dolomite outcrop cores to determine the oil recovery efficiency of surfactant systems, selected from their phase behavior test results, with potential to recover oil. Tridecyl alcohol 13 propoxy sulfate (TDS-13A) with an oil solubilization parameter of ~8 at reservoir salinity was found to recover greater than 75% oil in imbibitions experiments, at a concentration as low as 0.5wt%. The adsorption of surfactants on dolomite was measured at static and dynamic conditions; the adosprtion of TDS-13A was found to be ~ 0.26 – 0.34 mg/g reservoir rock. The effect of solution gas on surfactant phase behavior, up to 600-psi, was evaluated for methane, ethane, carbon-dioxide, and separator gas at 30°C. Methane had minimal effect on surfacatant optimal salinity, lowering it by ~2%/100psi solution gas, followed by carbon-dioxide which reduced it by ~11%/100psi. Ethane had a much more pronounced effect, reducing optimal salinity by ~46%/100psi solution gas.

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