Monitoring exogenous and indigenous bacteria by PCR-DGGE technology during the process of microbial enhanced oil recovery.

A field experiment was performed to monitor changes in exogenous bacteria and to investigate the diversity of indigenous bacteria during a field trial of microbial enhanced oil recovery (MEOR). Two wells (26-195 and 27-221) were injected with three exogenous strains and then closed to allow for microbial growth and metabolism. After a waiting period, the pumps were restarted and the samples were collected. The bacterial populations of these samples were analyzed by denaturing gradient gel electrophoresis (DGGE) with PCR-amplified 16S rRNA fragments. DGGE profiles indicated that the exogenous strains were retrieved in the production water samples and indigenous strains could also be detected. After the pumps were restarted, average oil yield increased to 1.58 and 4.52 tons per day in wells 26-195 and 27-221, respectively, compared with almost no oil output before the injection of exogenous bacteria. Exogenous bacteria and indigenous bacteria contributed together to the increased oil output. Sequence analysis of the DGGE bands revealed that Proteobacteria were a major component of the predominant bacteria in both wells. Changes in the bacteria population in the reservoirs during MEOR process were monitored by molecular analysis of the 16S rRNA gene sequence. DGGE analysis was a successful approach to investigate the changes in microorganisms used for enhancing oil recovery. The feasibility of MEOR technology in the petroleum industry was also demonstrated.