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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.

This work investigates the possibility of injecting dilute aqueous solutions of novel surfactants into the Yibal field (Sultanate of Oman). This was accomplished through an experimental protocol based on the following criteria: (i) compatibility of the surfactants with the high-saline reservoir water (~200 g/L); (ii) low interfacial tension (IFT) between crude oil and reservoir water (less than 10 -2 mN m -1 ); and (iii) maintaining the low IFT behavior during the entire surfactant flooding. Novel surfactants selected in this study consist of a series of ether sulfonates and an amphoteric surfactant (6-105). These surfactants were found to be compatible with reservoir water up to 0.1% surfactant concentration, whereas 6-105 and 7-58 showed compatibility within the full range of surfactant concentration investigated (0.001-0.5%). All surfactant systems displayed dynamic IFT behavior, in which ultralow transient minima were observed in the range 10 -4 -10 -3 mN m -1 , followed by an increase in the IFT to equilibrium values in the range 10 -3 -10 -1 mN m -1 . The results also showed that with respect to concentration (0.05-0.5 %) and temperature (45-80°C), AES-205 and 7-58 surfactants exhibit a wide range of applicability, with the IFT remaining below 10 -2 mN m -1 , as required for substantial residual oil recovery. In addition, ultralow IFT were obtained at surfactant concentrations as low as 0.001%, making the use of these surfactants in enhanced oil recovery extremely cost-effective.Paper no. S1524 in JSD 9, 287-293 (Qtr. 3, 2006). KEY WORDS: Compatibility, dynamic interfacial tension, surfactants, ultralow transient interfacial tension.Approximately 60% of the original oil in place (OOIP) will remain in an average oil reservoir after primary and secondary (water flooding in most cases) production. The residual oil is trapped in the reservoir pore structures by capillary forces and cannot be recovered by conventional means. Among the non-conventional techniques (known as enhanced oil recovery [EOR]) used to enhance oil production, surfactant flooding is one of the most appealing methods to enhance oil recovery from depleted reservoirs. In this technique, surfactants are added to the oil/water system to reduce the interfacial tension (IFT) from about 20-30 mN m -1 to less than 10 -2 mN m -1 (1,2). This seems to be a very simple method for recovering residual oil from reservoirs. However, from a technical point of view, there are some adverse conditions that prevent this technique from being successful in the field. The environment of an oil reservoir is often such that surfactants cannot generate this considerable reduction in surface tension as simply as described. One crucial aspect is that the water in these reservoirs is very salty (up to 200 g/L)-salinities above the solubility limits of most conventional surfactants used in EOR. Clearly, the compatibility of surfactants with reservoir brine is essential to avoid plugging of the porous medium, especially in reservoirs of low permeability. The other importa...

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