MICROBIAL COMPOSITION OF CARBONATE PETROLEUM RESERVOIR FLUIDS

Production fluids from four single-zone completion wells in carbonate petroleum reservoirs were examined chemically and microbiologically to investigate the potential for microbially enhanced oil recovery in ca rbonate reservoirs. The water analysis indicated a lack of soluble nit rogen and phosphorus in these reservoir fluids. Three of the wells wer e highly saline, as expected, but one produced water containing < 0.5% sodium chloride. Microorganisms with metabolisms useful for microbial ly enhanced oil recovery were enriched from the highly saline water pr oduced from these three wells. A small, but metabolically diverse, mic robial community was detected in each of the produced water samples. A lthough reservoir temperatures ranged from 44 to 63-degrees-C, the hig hest viable counts were obtained at mesophilic temperatures. The resul ts from this study are consistent with a hypothesis that, physical con ditions permitting, carbonate petroleum reservoirs contain microbial p opulations that could be stimulated for reservoir-wide in situ microbi ally enhanced oil recovery.