Abstract
Water flooding plays an important role in recovering oil from depleted petroleum reservoirs. Exactly how the microbial communities of production wells are affected by microorganisms introduced with injected water has previously not been adequately studied. Using denaturing gradient gel electrophoresis (DGGE) approach and 16S rRNA gene clone library analysis, the comparison of microbial communities is carried out between one injection water and two production waters collected from a working block of the water-flooded Gudao petroleum reservoir located in the Yellow River Delta. DGGE fingerprints showed that the similarities of the bacterial communities between the injection water and production waters were lower than between the two production waters. It was also observed that the archaeal composition among these three samples showed no significant difference. Analysis of the 16S rRNA gene clone libraries showed that the dominant groups within the injection water were Betaproteobacteria, Gammaproteobacteria and Methanomicrobia, while the dominant groups in the production waters were Gammaproteobacteria and Methanobacteria. Only 2 out of 54 bacterial operational taxonomic units (OTUs) and 5 out of 17 archaeal OTUs in the injection water were detected in the production waters, indicating that most of the microorganisms introduced by the injection water may not survive to be detected in the production waters. Additionally, there were 55.6% and 82.6% unique OTUs in the two production waters respectively, suggesting that each production well has its specific microbial composition, despite both wells being flooded with the same injection water.
Highlights
There is growing interest in the study of petroleum reservoir microbiota due to the prevalence of microbial enhanced oil recovery (MEOR) stimulated by increased global energy demand and depletion of oil reserves [1]
We investigate the microbial communities of injection water and its adjacent production waters in the Gudao petroleum reservoir which has been water flooded for over 30 years
Our results have indicated that there were a large number of unexplored microorganisms in the subsurface of the Gudao oil field
Summary
There is growing interest in the study of petroleum reservoir microbiota due to the prevalence of microbial enhanced oil recovery (MEOR) stimulated by increased global energy demand and depletion of oil reserves [1]. Microorganisms in the water recycling system are injected back into the reservoirs during the flooding process [8], which possibly caused the change of the microbial community structure of petroleum reservoir. Using DNA fingerprinting methods, such as denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) [14,15], several studies have compared the microbial communities of injection water and production waters. These studies revealed that community structures of injection and production waters are different. How the structure of subsurface microbial community is affected by injected microorganisms in water-flooded oil reservoirs has rarely been studied far
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