A thermophilic sulfate-reducing bacterium, Desulfucinum infernurn, is described. This bacterium was isolated from produced formation water from a North Sea petroleum reservoir. In liquid culture, the cells are oval, 1.5 by 2.5 to 3 pm, nonmotile and gram negative. Spore formation has not been observed. Growth occurs at temperatures ranging from 40 to 65"C, with optimum growth occurring at 60°C, and at levels of salinity ranging from 0 to 50 g of NaCl per liter, with optimum growth occurring in the presence of 10 g of NaCl per liter. D. infernurn grows on a range of organic acids, including formate, acetate, butyrate, and palmitate, and alcohols. D. infernum can grow autotrophically with H,. A vitamin supplement is required for growth. Sulfite and thiosulfate are used as electron acceptors. Sulfur and nitrate are not reduced. The DNA base composition is 64 mol% G+C. Phylogenetically, D. infernurn clusters with members of the delta subdivision of the Proteobucteriu. Its closest relatives are Syntrophobucter wolinii (level of similarity, 90.6%) and Desulfomonile tiedjei (level of similarity, 87.1%).Sulfate-reducing bacterial activity in petroleum reservoirs often is initiated through the introduction of water that is injected to improve oil recovery. This bacterial activity results in the production and accumulation of hydrogen sulfide. Crude oil containing significant levels of hydrogen sulfide is regarded as soured and has greatly reduced commercial value because of increased refining and processing costs. Hydrogen sulfide also has been recognized as a cause of corrosion damage in structures used for oil recovery and storage and as a cause of blockage of formation strata by iron sulfide, resulting in reduced oil production. In addition, hydrogen sulfide is an occupational health and safety hazard which has resulted in death of oil industry workers (2). The problems resulting from hydrogen sulfide production are believed to be primarily caused by introduced sulfate-reducing bacteria (17). However, recent evidence suggests that indigenous sulfate-reducing bacteria may be involved in souring (36).An understanding of the ecology of sulfate-reducing bacteria is essential if the adverse effects associated with hydrogen sulfide formation are going to be controlled. In this pursuit, a number of sulfate-reducing bacteria have been isolated from petroleum reservoirs. These include thermophilic sulfate-reducing bacteria, such as Thermodesulfobacterium mobile (formerly Desulfovibrio thermophilus The target reservoir used in this study (Beatrice, United Kingdom, North Sea) has been injected with seawater as a routine oil recovery practice. This has created a temperature gradient (40 to 115°C) between the wells used to inject the seawater and the wells used to produce formation fluids. Continuous injection of seawater has created a cool zone around the injection wells which is expanding toward the * Corresponding author. Fax: 61 6 251 6361. Electronic mail address: Rees@science.canberra.edu.au.producing wells. The temperature ...

Production waters from 36 high temperature petroleum reservoirs were examined for the presence of thermophilic, fermentative microorganisms.The direct supplementation of production waters with glucose and either yeast extract, peptone, tryptone or casamino acid resulted in the isolation of thermophilic. fermentative microorganisms from 47% of the petroleum reservoirs examined. Three distinctive morphological groups were isolated from the production waters of petroleum reservoirs with depths ranging from 396-3048 metres, temperatures ranging from 21-13O"C, salinities ranging from 2% 128 g l-' and pHs ranging from 6.0-8.5. Group 1 were pleomorphic rod-shaped bacteria, Group 2 were sheathed rod-shaped bacteria, and Group 3 were coccoid archaea. Partial characterisation of strains from one seawater-flooded petroleum reservoir and three non-watefflooded petroleum reservoirs tentatively identified some strains in Group 1 as members of the genera Thermoanuerobacter and Tl~ermoanaerobacteriu~?z, Group 2 as members of the Thermotogales order, and Group 3 as members of the genus Thermococcus. Production water salinity determined the type of microorganisms that were isolated. Group 1 organisms were found primarily in petroleum reservoirs with salinities less than 30 g/l, while Group 2 and 3 organisms were found to dominate in more saline reservoirs. The successful isolation of thermophilic, fermentative microorganisms from petroleum reservoirs decreased significantly with increasing salinity and temperature. These findings support the existence of a deep biosphere where fermentative microorganisms are widespread.

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Desulfobacterium vacuolatum strain IbRM was able to grow using casamino acids as a source of carbon, energy and nitrogen. Growth was accompanied by utilization of several amino acids and sulfide production. Proline and glutamate were used preferentially and to the greatest extent. Glycine, serine and alanine were used more slowly and only after proline and glutamate were used. Isoleucine, valine, leucine and aspartate decrease was slowest and occurred in a linear fashion throughout the growth phase. Amino acids used from casamino acids, excluding aspartate, were also used as single carbon, energy and nitrogen sources. As a single amino acid, aspartate could only be used as a nitrogen source. Aspartate was not used as an electron acceptor. No growth occurred on any amino acid in the absence of sulfate. As single substrates, isoleucine, proline and glutamate were oxidized without formation of acetate and with molar yields of 13.1, 9.4 and 7.7 g mol-1, respectively.

A microbial enhanced-oil-recovery (MEOR) process was successfully applied in a mature waterflooded reservoir in Saskatchewan, Canada. A nutrient solution, which was designed specifically for this reservoir to stimulate indigenous microbes to grow, multiply, and help to release oil, was tested and piloted. A significant decrease in water cut and increase in oil production have been realized through the selective stimulation of bacteria using nutrient injection. The field is a mature waterflood averaging more than 95% water cut. To combat the increasing water-cut issue, an in-situ microbial response analysis (ISMRA) was performed on a typical high-water-cut producer in the area. The test well was treated with a nutrient solution and then was shut in for a number of days to allow indigenous microbes to grow and multiply. Upon return to production, the well produced at an average of 200% more oil with a 10% decrease in water cut for a year. Pretreatment rates averaged 1.2 m 3 /d of oil (8 BOPD) and post-ISMRA treatment daily production peaked at 4.1 m 3 /d of oil (26 BOPD). The ISMRA provides a direct support of laboratory studies and frequently increases oil production. As a result of the successful ISMRA, a pilot project was initiated and the nutrients were applied in three batch treatments on an injector with three offset production wells. Three weeks after the first batch treatment, a water-cut decrease was seen at one of the offset producers. This well's oil production gradually increased from 1.4 to more than 8 m 3 /d (9 to 50 B/D). Oil production in another producer doubled from 1.5 to more than 3.0 m 3 /d (9 to 19 B/D). Subsequent treatments were tried on marginally economic wells and on a reactivated idle producer. The average decrease in water cut in these wells was more than 10%. On the idle well, oil production increased from 0.5 m 3 /d (3 B/D) pretreatment to an average of 3.0 m 3 /d (19 B/D) post-treatment. Throughout the world, there remains a huge target for enhancedoil-recovery (EOR) processes to target (Bryant 1991). This successful MEOR application will have a tremendous impact on ultimate recovery in many of these reservoirs not only through an increase in production, but a decrease in operating costs through associated reduction in lifting costs with less water production.