Microbial community analyses of produced waters from high-temperature oil reservoirs reveal extraordinary similarity between geographically distant oil reservoirs

Abstract

Microbial enhanced oil recovery (MEOR) is a low-cost and environmentally-friendly alternative to thermal or chemical oil recovery techniques. In order to consider the application of MEOR for high-temperature oil reservoirs (65 - 80 $^\circ C$), we investigated the indigenous microbial community compositions of produced waters from five different mid-temperature oil reservoirs near Segno, TX, USA (80-85 $^\circ C$) and Crossfield, AB, Canada (75 $^\circ C$). The DNA samples extracted from the sparsely populated produced water samples were analyzed with Miseq amplicon sequencing of partial 16S rRNA genes. These sequences were analyzed along with additional sequence data retrieved from the public database and through personal communication, which included sequence data from six oil fields in Louisiana, USA (28-45 $^\circ C$), two oil fields in Xinjiang, China (22-35 $^\circ C$) and a subseafloor oil reservoir below the Norwegian Sea (83 - 86 $^\circ C$), and an off-shore oil field (Halfdan) in the North Sea off the coast of Denmark (75 - 86 $^\circ C$). Despite the geographical distance and difference in the chemical compositions, the OTU compositions of the Segno and Crossfield sites exhibited high similarity, as indicated by the results of beta diversity analyses. The major groups of recovered OTUs included members of the Clostridiaceae, Methanosaetaceae, Thermotogaceae, which have been recognized to be thermophilic, thermotolerant, or spore-forming taxa that have diverse metabolic potentials. The sequence data retrieved from the database exhibited different clustering patterns, as the samples from close geographical locations had low beta diversity and the physicochemical properties of the reservoirs apparently did not have a substantial role in shaping of microbial communities. The correlation network analyses revealed that the major OTUs in Segno and Crossfield samples formed a single tight network.