Optimization of a Low-Concentration Bacillus subtilis Strain Biosurfactant toward Microbial Enhanced Oil Recovery

Abstract

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, 2.5×, 5×, 10×, and 20× 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 10× 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 (Na 2 CO 3 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.

Isolation and screening of Bacillus subtilis MJ01 for MEOR application: biosurfactant characterization, production optimization and wetting effect on carbonate surfaces

“…The ideal limit is the maximum feasible yield of biosurfactant, and the economical limit is the yield of biosurfactant by considering two important facts. The first evidence is that the extraction of biosurfactant from culture medium is not feasible both technically and economically; therefore, the raw biosurfactant in culture broth could be used directly for the injection process (Rabiei et al 2013;Sarafzadeh et al 2013;Souayeh et al 2014). The second fact is the components of culture medium should be compatible with reservoir connate water to prevent formation damage.…”

“…From the petroleum engineering point of view, extraction of the biosurfactant in order to use in MEOR process would add extra cost while no significant excess oil recovery could be obtained (Rabiei et al 2013;Sarafzadeh et al 2013; Souayeh et al 2014). It means that instead of pure solution of biosurfactant, biosurfactant in the culture (without extraction) should be injected to reservoir without any recycling of nutrient components.…”

Production of lipopeptide biosurfactants by Bacillus atrophaeus 5-2a and their potential use in microbial enhanced oil recovery

“…Therefore, biosurfactants reduce surface tension and interfacial tension in both aqueous solutions and hydrocarbon mixtures and form micelles and microemulsions between the two phases [ 2 , 3 ]. Such surface properties make biosurfactants good candidates for enhancing oil recovery [ 4 , 5 ]. Bailey et al [ 6 ] reported that a biosurfactant flooding process, using a low concentration (35–41 ppm) of biosurfactants produced by Bacillus mojavensis strain JF-2, resulted in high oil recovery, of up to 35–45 %.…”

“…In recent years, an increase in concern about environmental protection has caused the development of cost-effective bioprocesses for biosurfactants production [ 7 ]. The use of biosurfactants that have a comparable enhanced oil recovery performance is preferable [ 4 ].…”

Characterization and Application of Biosurfactant Produced by Bacillus licheniformis R2

“…The main constraints in reducing the cost of biosurfactant market are from the downstream processing [2]. Whereas, the advantage of using biosurfactants in oil industries are that high grade of purity is not required and can be used in crude form, unlike in medicinal or food applications, and can be used at higher dilutions for the field applications [8].…”