ds along with kerosene. The amount of released bitumen was compared with controls run with only kerosene added to tar sands. The biosurfactant enhanced the release of bitumen.
Generally the organisms that produce surfactants are aerobes. However, Cooper et al. (3) isolated a neutral lipid biosurfactant from the anaerobe Clostridium pasteurianum, and an anaerobic biosurfactant from a Bacillus sp. was recently reported (4).
Several combinations of surfactants and bacteria have been suggested for use in EOR drive fluids. Harvey (5) patented a process using dead bacterial and/or yeast cells to carry nonionic surfactants [poly-(ethylene oxide) ethers or thioethers] as EOR slugs through the reservoir. Using such slugs in laboratory sand column reservoir models, he obtained 20 to 30% recovery of residual oil. Hitzman (6) and Wagner and Stratton (7) claim that commercial surfactant-treated dead bacterial cells can be used effectively in EOR drive fluids, without the need for injecting live bacterial cells into a reservoir for effective channeling of the injection water.
Recently a Swiss biotechnology company announced plans to field test three biosurfactants in the United States. They utilize continuous culture methods (fermentation apparatus) for the production of these compounds (8).
Hussain et al. (9) suggested the use of bacterially produced polysaccharides (dextrans) as floodwater thickening agents. Lindblom et al. (10) documented the use of Xanthomonas sp. to ferment glucose and produce a thermally stable heteropolysaccharide that can be used in waterflooding systems. Using a model reservoir in the laboratory, they injected an aqueous mixture of the polysaccharide (xanthan gum) and 50 x 103 ppm sodium chloride. By using data from these experiments they showed that the properties of the xanthan gum were not altered by the sodium chloride. Precipitation and plugging of the model reservoir also did not occur. Processes based on the uses of xanthan gum in EOR are: (a) use of biopolysaccharides to thicken injection waters; (b) use with other chemicals, which are sacrificial adsorption agents to prevent adsorption of the polysaccharide on to rock surfaces; (c) use with multivalent cations to bind the polysaccharide molecules together (crosslinking) for preferential partial plugging of the reservoir to prevent water channeling; and (d) use with gel particles, hydrolyzed polyacrylamides, and ferric chloride solutions to assist in the water-thickening process.
Since Lindblom's patent, several laboratories have investigated the production of xanthan gum. It is now used commercially as a mobility control agent for EOR. Its properties of viscosity, shear resistance, and temperature and salt tolerance make it almost an ideal polymer for use in EOR. It is considered superior to polyacrylamides for the above reasons, but it is more expensive (11) and more susceptible to bacterial degradation (12).
Another biopolymer, scleroglucan, is produced by species of the fungus Sclerotium. These polymers were examined for possible use in EOR (13). The scleroglucans are neutral polysaccharides with a cellulose-type backbone (14). Scleroglucan and xanthan gum possess similar rheological properties. Sclerotium sp. can grow on a variety of carbon and energy sources. It is postulated that the fungus can grow on waste plant material such as hydrolyzed lignin and other industrial wastes, and produce the polymer. These nutrients would be less expensive than hydrocarbons or most other commercially available ones (13).
Under favorable conditions and in a liquid culture, bacteria can ferment carbohydrates to produce gases such as CO2 and H2. Such gases produced in situ can contribute to re-pressurization of a pres-
sure-depleted petroleum reservoir. These gases also may dissolve in the crude oil and reduce its viscosity. Additional benefits of this bacteria-induced fermentation process are the production of acids, such as acetic and propionic acids, which can dissolve carbonate rock and increase its permeability and porosity, and the production of solvents, s