Experiments focused on tertiary oil recovery of waterflood residual oil using a bio-surfactant flooding process are reported in this paper. Significant quantities of water flood residual oil were recovered when very low concentration bio-surfactant solutions were flooded through 25-200 md Berea sandstone cores. The residual oil recovery ranged between 35% and 45% as surfactant concentrations varied from 35-41 ppm.

Cleaned and dried Berea sandstone cores, six inches long and one and half inches in diameter with an average porosity of 16.0 % were first saturated with 5.0% NaCl brine, then saturated with 340 API crude oil and finally waterflooded to near residual oil saturation. Thirty five to forty five percent of that residual oil was recovered when the cores were flooded with surfactant combined with a 0.001% by vol. co-surfactant alcohol and 1000 ppm of partially hydrolyzed polyacyalamide (PHPA) as mobility control polymer. The co-surfactant alcohol was added to reduce the effect of salinity.

The bio-surfactant concentrations reported are much lower than those previously reported in synthetic surfactant laboratory tests. The oil recovery in terms of bio-surfactant consumed is also substantially higher than previous surfactant tests. This tertiary recovery process may help improve oil recoveries from many marginal oil fields operating a waterflood that produce small amounts of oil at high water cuts or those that have been abandoned due to uneconomic operating costs but still contain significant amounts of oil.

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