--> Phospholipid Fatty Acid Evidence of Recent Microbial Life in Pristine Marcellus Shale Cores

AAPG Eastern Section Meeting

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Phospholipid Fatty Acid Evidence of Recent Microbial Life in Pristine Marcellus Shale Cores

Ryan V. Trexler1, Rawlings Akondi2, Susan M. Pfiffner3, Rebecca A. Daly4, Michael J. Wilkins5, Shikha Sharma2, Kelly C. Wrighton4 and Paula J. Mouser1

1 Department of Civil, Environmental, and Geodetic Engineering, The Ohio State University, Columbus, OH
2 Department of Geology and Geology, West Virginia University, Morgantown, WV
3 Center for Biotechnology, University of Tennessee, Knoxville, TN
4 School of Earth Sciences, The Ohio State University, Columbus, OH
5 Department of Microbiology, The Ohio State University, Columbus, OH

September 27, 2016 Tuesday 3:30 P.M. AAPG Eastern Section Meeting, Lexington, Kentucky

Abstract

Organic-rich black shales are currently being targeted for natural gas development in formations across the U.S. Several studies have shown microbial communities exist in wells after hydraulic fracturing, but it is not known whether these microorganisms derive from the pristine shale before energy development. Previous research has characterized phospholipid fatty acids (PLFAs) in Cenozoic and Mesozoic aged shales yet, no measurements have been reported for Paleozoic-aged black shales such as the Marcellus. Here, we report the first measurements of PLFAs in pristine cores originating from a scientific well at the Marcellus Shale Energy and Environment Laboratory (MSEEL) near Morgantown, West Virginia. We focused on sidewall core samples spanning the interface between the Marcellus and Mahantango formations. Sidewall cores were collected and cleaned using successive brine washes, microscopy verified removal of fluorescent tracers, surface sterilized cores were ground to a particle size less than 500 µm, and cores were homogenized. Lipids were extracted and methylated from six samples (three sidewall cores, the washing brine, and two drilling muds) and the resulting PLFA methyl esters (PL-FAMEs) were analyzed using GC-MS. Drilling muds had 37-fold higher biomass compared to the core samples and shared only common normal saturated PL-FAMEs, indicating minimal contamination from surface-derived microorganisms after cleaning. In pristine core samples, the Marcellus and Mahantango had similar biomass and similar numbers of PL-FAMEs. However, the Marcellus shale had a 14-fold increase in hydroxy-PL-FAMEs compared to the Mahantango as well as a minor amount of polyunsaturated PL-FAMEs. Notably, the presence of keto- and hydroxyl-PL-FAMEs in all three cores suggest potential acclimatization of the microbial community to environmental stress. Our data indicate the Marcellus and Mahantango formations may harbor recent microbial life that is acclimated to deep biosphere conditions prior to shale gas development.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016