Assessing Microbial Activity in Marcellus Shale Hydraulic Fracturing Fluids
Monday, 15 December 2014
Hydraulic fracturing (HF) produces millions of gallons of waste fluid which contains a microbial community adapted to harsh conditions such as high temperatures, high salinities and the presence of heavy metals and radionuclides. Here we present evidence for microbial activity in HF production fluids. Fluids collected from a Marcellus shale HF well were supplemented with 13C-labeled carbon sources and 15N-labeled ammonium at 25°C under aerobic or anaerobic conditions. Samples were analyzed for 13C and 15N incorporation at sub-micrometer scale by ion imaging with the JAMSTEC NanoSIMS to determine percent carbon and nitrogen assimilation in individual cells. Headspace CO2 and CH4 were analyzed for 13C enrichment using irm-GC/MS. At 32 days incubation carbon assimilation was observed in samples containing 1 mM 13C-labeled glucose under aerobic and anaerobic conditions with a maximum of 10.4 and 6.5% total carbon, respectively. Nitrogen assimilation of 15N ammonium observed in these samples were 0.3 and 0.8% of total nitrogen, respectively. Head space gas analysis showed 13C enrichment in CH4 in anaerobic samples incubated with 1mM 13C-labeled bicarbonate (2227 ‰) or methanol (98943 ‰). Lesser 13C enrichment of CO2 was observed in anaerobic samples containing 1 mM 13C-labeled acetate (13.7 ‰), methanol (29.9 ‰) or glucose (85.4 ‰). These results indicate metabolic activity and diversity in microbial communities present in HF flowback fluids. The assimilation of 13C-labeled glucose demonstrates the production of biomass, a critical part of cell replication. The production of 13CO2 and 13CH4 demonstrate microbial metabolism in the forms of respiration and methanogenesis, respectively. Methanogenesis additionally indicates the presence of an active archaeal community. This research shows that HF production fluid chemistry does not entirely inhibit microbial activity or growth and encourages further research regarding biogeochemical processes occurring in Marcellus shale HF wells. Biogeochemical activity may impact the efficacy of HF and natural gas production as well as the chemistry of produced fluids which have become an environmental and public health concern.