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Biosurfactant production using Candida bombicola ATCC 22214, its characterization and potential applications in enhancing oil recovery were studied at laboratory scale. The seed media and the production media were standardized for optimal growth and biosurfactant production. The production media were tested with different carbon sources: glucose (2%w/v) and corn oil (10%v/v) added separately or concurrently. The samples were collected at 24 h interval up to 120 h and checked for growth (OD660), and biosurfactant production [surface tension (ST) and interfacial tension (IFT)]. The medium with both glucose and corn oil gave better biosurfactant production and reduced both ST and IFT to 28.56 + 0.42mN/m and 2.13 + 0.09mN/m, respectively within 72 h. The produced biosurfactant was quite stable at 13–15% salinity, pH range of 2–12, and at temperature up to 100°C. It also produced stable emulsions (%E24) with different hydrocarbons (pentane, hexane, heptane, tridecane, tetradecane, hexadecane, 1-methylnaphthalene, 2,2,4,4,6,8-heptamethylnonane, light and heavy crude oil). The produced biosurfactant was extracted using ethyl acetate and characterized as a mixture of sophorolipids (SPLs). The potential of SPLs in enhancing oil recovery was tested using core-flooding experiments under reservoir conditions, where additional 27.27% of residual oil (Sor) was recovered. This confirmed the potential of SPLs for applications in microbial enhanced oil recovery.

Crude oil is the major source of energy worldwide being exploited as a source of economy, including Oman. As the price of crude oil increases and crude oil reserves collapse, exploitation of oil resources in mature reservoirs is essential for meeting future energy demands. As conventional recovery methods currently used have become less efficient for the needs, there is a continuous demand of developing a new technology which helps in the upgradation of heavy crude oil. Microbial enhanced oil recovery (MEOR) is an important tertiary oil recovery method which is cost-effective and eco-friendly technology to drive the residual oil trapped in the reservoirs. The potential of microorganisms to degrade heavy crude oil to reduce viscosity is considered to be very effective in MEOR. Earlier studies of MEOR (1950s) were based on three broad areas: injection, dispersion, and propagation of microorganisms in petroleum reservoirs; selective degradation of oil components to improve flow characteristics; and production of metabolites by microorganisms and their effects. Since thermophilic spore-forming bacteria can thrive in very extreme conditions in oil reservoirs, they are the most suitable organisms for the purpose. This paper contains the review of work done with thermophilic spore-forming bacteria by different researchers.

Summary This study aims to test the potential of microbial enhanced oil recovery (MEOR) as an effective alternative in Omani oil fields. In this study, biosurfactants produced by Bacillus licheniformis and Bacillus subtilis strains isolated from oil-contaminated soils from different parts of the Sultanate of Oman were investigated. Eight different minimal production media using different sugars as carbon sources were tested on three of the strains to select the medium that maximized the production of biosurfactants which were indicated by the interfacial tension (IFT) reduction. All isolates were tested on their potential media to screen for the best biosurfactant producer among the available strains. It was found that Bacillus subtilis Strain W19 gave the maximum IFT reduction (46.6 mN/m to 3.28 mN/m) in 16 hours of incubation when grown in a minimal medium containing glucose. The yield of the biosurfactant produced by B. subtilis W19 was 2.5g/L. Critical micelle concentration (CMC) was measured to be 0.4 g/L. The biosurfactant was partially characterized by FT-IR analysis, in which the peaks obtained imply the presence of aliphatic hydrocarbons as well as a peptide-like moiety in the biosurfactant. The cell-free biosurfactant broth produced from Strain W19 was found to be stable over a pH range from 6 to 10 and was most effective at 7. It also showed no loss in surface activity when subjected to various temperatures (60, 80, and 120°C). The biosurfactant also retained almost 60% of its activity even in a high-saline environment up to 20% NaCl (w/v). Further studies were conducted to test the interaction of biosurfactant produced by B. subtilis W19 with porous media in coreflooding experiments as a tertiary-recovery stage. The results showed high potential of using this bacterium during ex-situ MEOR applications in which a total of 23% of residual oil was produced after biosurfactant and concentrated-biosurfactant injection.

In this study, a biosurfactant produced by a Bacillus subtilis strain isolated from oil-contaminated soil from an Omani oil field was tested for its potential in enhancing oil recovery by a series of coreflooding experiments. It was found that the performance of the biosurfactant was increased by mixing with chemical surfactants, by which the maximum production went up to 50% of residual oil at a mixing ratio of (50:50). The second objective of this study was to investigate the effects of the biosurfactant on wettability alteration and to estimate its tendency to loss caused by adsorption. The influence of biosurfactant on wettability was studied by contact-angle measurements, atomic force microscopy (AFM) technique on few-layer graphene (FLG) surfaces, and Amott wettability tests on Berea sandstone cores. Contact-angle measurements showed that the wettability of the biosurfactant solution changes to more oil-wet as the angle decreased from 70.6 to 25.32° when treated with 0.25% (w/v) biosurfactant solution. Amott testing showed a change in wettability index from strongly water-wet in the untreated core toward less water-wet in biosurfactant-treated cores. These results confirmed the ability of the biosurfactant to alter the wetting conditions against different surfaces, thereby serving as a mechanism for enhancing oil recovery. The maximum loss of biosurfactant caused by adsorption was 1.2 mg/g of rock, which is comparable with reported chemical-surfactant values.