Freshwater microbial communities from methane shale flowback fluids - Sample_06272012
Recent advances in horizontal drilling coupled with hydraulic fracturing techniques have made it possible to extract large volumes of oil and natural gas from methane shale formations located more than a mile below ground surface. The Marcellus and Utica-Point Pleasant shales in the Ohio-Pennsylvania region represent two formations projected to produce large energy resources over the next 25 years [1]. Although Marcellus and Utica core chemistry has been studied [2], the challenges associated with drilling and sampling at these depths have limited the collection of pristine samples from which to benchmark indigenous microbial populations in these rocks. Our current conceptual model based on wellhead fluids and sparse core observations is that diagenesis temperatures effectively sterilized these formations, and current physicochemical conditions (inc. pressures greater than 50 MPa, temperatures above 60oC, 20% salt content, and pore sizes less than 1 µm) have limited microbial growth to discrete fracture zones that are connected to regional fluid circulation patterns [2, 3]. The injection of millions of gallons of fluid introduces labile polymeric carbon sources and surface microorganisms to these depths that may colonize new fractures, thereby altering the microbial ecology and biogeochemistry in unknown ways. The fracturing and perturbation of these formations at the current scale has resulted in a significant uncharacterized subsurface environment that may be indefinitely altered through these activities. Over 7,000 Marcellus shale gas wells were active during 2012 in Pennsylvania [4], and Ohio is expecting a similar level of development over the next 5 years. Understanding microbial survivability and the metabolic potential of organisms that persist are key to elucidating the long-term impacts these technologies will have on deep subsurface microbiota and shale biogeochemistry.