Environmental Drivers of Differences in Microbial Community Structure in Crude Oil Reservoirs across a Methanogenic Gradient

Abstract

Stimulating in situ microbial communities in oil reservoirs to produce natural gas is a potentially viable strategy for recovering additional fossil fuel resources following traditional recovery operations. Little is known about what geochemical parameters drive microbial population dynamics in biodegraded, methanogenic oil reservoirs. We investigated if microbial community structure was significantly impacted by the extent of crude oil biodegradation, extent of biogenic methane production, and formation water chemistry. Twenty-two oil production wells from north central Louisiana, USA, were sampled for analysis of microbial community structure and fluid geochemistry. Archaea were the dominant microbial community in the majority of the wells sampled. Methanogens, including hydrogenotrophic and methylotrophic organisms, were numerically dominant in every well, accounting for, on average, over 98% of the total Archaea present. The dominant Bacteria groups were Pseudomonas, Acinetobacter, Enterobacteriaceae, and Clostridiales, which have also been identified in other microbially-altered oil reservoirs. Comparing microbial community structure to fluid (gas, water, and oil) geochemistry revealed that the relative extent of biodegradation, salinity, and spatial location were the major drivers of microbial diversity. Archaeal relative abundance was independent of the extent of methanogenesis, but closely correlated to the extent of crude oil biodegradation; therefore, microbial community structure is likely not a good sole predictor of methanogenic activity, but may predict the extent of crude oil biodegradation. However, when the shallow, highly biodegraded, low salinity wells were excluded from the statistical analysis, no environmental parameters could explain the differences in microbial community structure. This suggests that the microbial community structure of the 5 shallow, up-dip wells was different than the 17 deeper, down-dip wells. Also, the 17 down-dip wells had statistically similar microbial communities despite significant changes in environmental parameters between oil fields. Together, this implies that no single microbial population is a reliable indicator of a reservoir's ability to degrade crude oil to methane, and that geochemistry may be a more important indicator for selecting a reservoir suitable for microbial enhancement of natural gas generation.

Comparative metagenomics of coalbed methane microbial communities reveals biogenic methane potential in the Appalachian Basin

“…Taxonomic profiling of metagenome reads revealed that Appalachian Basin metagenomes contained varied proportions of Archaea and Bacteria, with the relative abundance ranging from 1–81%, and 19–99%, respectively (Figure 1). The relative abundance of Archaea was >48% for five of the eight metagenomes, greater than what has been found in other coalbed basins 6–8 , but similar to Archaea abundances in crude oil reservoirs 28 .…”

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

“…The microbial community profiles of the Crossfield and Segno produced waters were analysed in depth alongside the microbial community profiles of produced waters from other oil reservoirs of varying geographical locations and physicochemical characteristics (Table S4). Comparisons were constructed with the raw 16S rRNA amplicon sequence data sets acquired from the NCBI Sequence Read Archive (SRA) and through personal communication (Lewin et al, 2014;Gao et al, 2015;Hu et al, 2016;Shelton et al, 2016;Li et al, 2017;Vigneron et al, 2017). As expected from the nearly identical microbial compositions of the Crossfield and Segno samples, tight clustering was observed for the microbial communities in these samples, regardless of the metrics used for beta diversity calculation (Fig.…”

Anaerobic microbial communities and their potential for bioenergy production in heavily biodegraded petroleum reservoirs

“…This strategy may be more feasible for residual lighter oils, where it is estimated that an additional production of 5%-10% of the oil mass may be recovered, increasing the lifetime of these reservoirs (Jiménez et al, 2016). Strategies for in situ conversion of oil-to-methane, in addition to being driven by the natural gas market, will thus be determined by conditions specific to given oil field operations (Shelton et al, 2016). In this context, the present work highlights that the extent of pre-existing biodegradation is an important determinant and suggests that heavy oils are poor candidates as feedstocks for further biological conversion by resident microbial communities.…”