The lipopeptide biosurfactant produced by Bacillus subtilis strain W19 was investigated for the potential to maintain additional oil recovery at different dilutions and concentrations and in combination with synthetic chemical surfactant or alkali. The effect of salinity on the biosurfactant performance and the effect of biosurfactant on permeability reduction were also studied, at reservoir conditions. Core-flooding experiments were conducted to quantify the biosurfactant dosage for optimized enhanced oil recovery. Berea sandstone cores with respective average gas permeability and porosity of 223 mD and 21.5%, crude oil of American Petroleum Institute (API) gravity of 32°, and formation brine with salinities ranging from 7 to 9% were used. Biosurfactant reduced the interfacial tension (IFT) between the aqueous phase and crude oil from 20.9 to 1.8 mN/m. In core flood tests with cell-free biosurfactant broth at different dilutions (undiluted, 2.5x, 5x, 10x, and 20x diluted) and using crude biosurfactant powder (1 and 0.4 g/L), we observed additional 15 and 13% oil recovery over residual water-flood oil saturation, respectively. These results confirmed that a minimal biosurfactant concentration required for effective oil recovery was 0.4-0.5 g/L. Because biosurfactant broth is more economical then extracting biosurfactant, we have used it for further experiments. Salinity effect studies on oil recovery showed that this biosurfactant can maintain an additional recovery of 20% even at up to 20% (w/v) salinity. A mixture of 10x diluted biosurfactant with chemical surfactant to the ratio of "75:25", respectively, resulted in 28% additional recovery, which was better than using either alone. Mixing of biosurfactant with alkaline (Na2CO3 at 0.5 and 1.0% concentrations) resulted in further reduction of IFT by a factor of 10, but no further improvement of oil recovery was observed. Diluted biosurfactant also showed very minimal reduction in permeability of sandstone cores. This study showed that the biosurfactant would produce an appreciable amount of additional oil after water-flooded residual oil at a low concentration, without much formation damage, and its performance can be improved even further by mixing it with chemical surfactants.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Fuel Technology
- Energy Engineering and Power Technology