S4: Bacterial communities associated with drilling, hydraulic fracturing and early production stages in thermogenic natural gas wells of the Barnett shale

The Barnett Shale in north central Texas contains natural gas generated by high temperatures (120 to 150°C) during the Mississippian Period (300 to 350 million years ago). In spite of the thermogenic origin of this gas, biogenic sulfide production and microbiologically induced corrosion have been observed at several wells in this formation. We monitored the structure, abundance, and activity of microbial communities associated with drilling, hydraulic fracturing, and early stages of production in multiple wells in the Barnett shale. Our goal was to identify how current field practices modulates bacterial community in the Barnett, and how such an understanding could lead to practical recommendations for controlling the deleterious effect of microorganisms e.g. souring, biocorrosion. We demonstrate that: 1. The current mud formulation practices and chemical composition stimulates microbial growth in drilling waters and primes the microbial community for survival in the shale formation, 2. During hydraulic fracturing, biocide treatments does not eliminate all bacteria from waters injected to the formation, and the bacterial community recovered in flowback water is highly adapted to the in-situ conditions in the formation. And 3. Bacterial communities developed in above ground production facilities are highly dissimilar to bacterial communities in drilling and hydraulic fracturing fluids. Finally, several of the phylotypes observed in this study belonged to lineages that were thought to be indigenous to marine and terrestrial fossil fuel formations. Our results suggest a possible alternative exogenous origin of such phylotypes via enrichment during the drilling and hydraulic fracturing processes.