Microbial Activity in Hydraulic Fracturing Produced Water from Two Shale Gas Reservoirs

As shale gas has become one of the nation’s most important fossil fuels, it is increasingly important to monitor groundwater near shale gas wells to ensure there is no impact from drilling operations. The microbial activity within these shale gas reservoirs have the potential to alter the groundwater flow and groundwater chemistry through biogeochemical processes such as acid production, sulfate reduction, and biofilm formation. While these microbial communities are expected to impact monitoring strategies, little is known about the dominant microbial processes that will occur.

The goal of this study is to better define the microbiology of two major shale gas reservoirs, the Marcellus Shale in the Appalachian region, and the Bakken Shale in the North Dakota region. Metagenomic analysis was completed for 42 Marcellus Shale produced water samples and 64 Bakken Shale produced water samples. Bakken samples contained microbial loads 3 to 4 orders of magnitude below those observed for Marcellus samples. Microbial community structure analysis using 16S rRNA sequencing suggested samples to be dominated by the order Bacillales, Halanaerobiales, and Pseudomonadales. The role Halanaerobiales was further investigated by reconstructing and annotating a Halanaerobium draft genome. Reconstruction of metabolic pathways revealed Halanaerobium to have the potential for acid production, sulfide production, and biofilm formation, suggesting potential impact on groundwater quality. Data from this study extends the current knowledge of microbial processes within hydraulic fracturing produced water system, and will contribute to the development of better montioring strategies in the future.