The drilling and completion of shale oil and gas wells creates a newfound, highly selective ecosystem that microorganisms inhabit. Despite the growing body of knowledge pertaining to the patterns of microbial community succession and metabolic potential in flowback and produced water, fundamental details related to microbial origin and persistence in fractured shale systems are lacking. Lipid biomarker analyses applied to shale cores and produced fluids can provide insights into microbial life history, viability, community structure, and physiological strategies employed to adapt to selective environments. Here, the utility of lipid biomarker analyses using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was leveraged to characterize the microbial biomass composition associated with a Marcellus Shale natural gas well before and after well completion. In total, nine sidewall rock cores from five target formations, two input fluids, and twelve flowback and produced water samples collected over 490 days were surveyed for microbial membrane lipids. Remnant archaeal glycerol dialkyl glycerol tetraether lipids were detected in a limestone core sample, in addition to archaeol in some other rock cores, suggesting living archaea were once present in the deep terrestrial subsurface. Temporal trends in microbial biomass in the flowback and produced water revealed a predominance of bacterial phospholipids and unique glycophospholipids having anionic, glycosylated, and tentatively identified acylated head groups. Considering fluid bulk geochemistry and the consistent high abundance of these lipid head groups, we surmise these structures contribute to (1) the stability of cellular membranes under osmotic stress and (2) the selectivity of membrane permeability. The detected lipid head groups may serve as chemotaxonomic biomarkers for heterotrophic, halophilic bacteria residing in highly saline fluids retained in terrestrial environments. Taken together, this research advances our fundamental understanding of microbial adaptation and persistence in fractured shale systems.

Microbial lipid biomarkers in a Marcellus Shale natural gas well: From remnant molecules to adapted communities

255th National Meeting (2018)

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