PRETEST STUDIES FOR A MICROBIALLY ENHANCED OIL-RECOVERY FIELD PILOT IN A HYPERSALINE OIL-RESERVOIR

The ecological and physiological factors governing microbial activity in the Southeast Vassar Vertz Sand Unit (SEVVSU), Payne County, OK, an oil reservoir selected for a microbially enhanced oil recovery field pilot, were studied. Analysis of the brines from the reservoir showed that the SEVVSU reservoir is a hypersaline environment rich in calcium and magnesium cations, and contains most of the inorganic nutrients r equired for microbial growth Substantial amounts of sulfate and sulfid e were detected in the brines, indicating a potential for sulfate redu ction activity. Of the various carbohydrate-based nutrients tested, a molasses-ammonium nitrate nutrient mixture best stimulated the metabol ism and growth of the microbial communities in the brines Sulfide was not detected in any brine samples that received high levels of nitrate , even when additional carbon sources such as molasses were added. The addition of nitrate also resulted in shorter lag times, higher maximu m turbidities, and larger pressure increases due to gas production. Ae robic heterotrophic bacteria, anaerobic heterotrophic bacteria, anaero bic molasses nitrate-using bacteria, sulfate-reducing bacteria, and me thanogenic bacteria capable of growing at high salt concentrations wer e detected in all the brines. Several bacterial strains were isolated, five of which were further characterized. All five isolates were stri ctly anaerobic and obligately halophilic, requiring a minimum of 6-9% NaCl (w/v) for growth in complex medium. Glucose was fermented to H-2, CO2, ethanol, and acetate by all the five strains. In spite of the hi gh salinity, the SEVVSU reservoir contains an active microbial communi ty whose metabolism and growth can be stimulated by the addition of ca rbohydrate-based nutrients.