Analysis of Microbial Lipid Biomarkers as Evidence of Deep Shale Microbial Life

Abstract

The presence of native, viable microbial life from deep shale formations has ramifications on the extraction and production of oil and natural gas resources in the US. Wells at the Marcellus Shale Energy and Environment Laboratory (MSEEL) near Morgantown, West Virginia, have provided unprecedented access to pristine shale cores to probe microbial life at borehole depths reaching 7500 feet below the surface. Lipid biomarker-based analyses applied to shale can provide insights to microbial life history, viability, community structure, and physiological strategies employed to cycle carbon and survive extreme environmental conditions. Preliminary analysis of phospholipids from cores in the upper Marcellus indicated recent life exists at some depths in the formation with biomarker signatures differing from those in drilling muds. However, the shale chemical matrix and low microbial biomass present multiple challenges therefore, developing optimal methods for extracting and analyzing these biomarkers is of paramount importance. This research details our continued methods optimization process for characterizing microbial lipid biomarkers from pristine sidewall core samples obtained from MSEEL. We present strategies to maximize the recovery and preservation of bacterial and archaeal lipid signatures, as well as purification and chromatographic separation techniques used to isolate intact polar lipids, which are indicators of viable microbes. Direct analysis of intact polar bacterial and archaeal lipids through the use of ultra-performance liquid chromatography coupled with tandem mass spectrometry systems is also discussed. Lastly, the identification of non-polar lipid constituents using gas chromatography-mass spectrometry is described with emphasis placed on differentiating modern and ancient biomolecules. These methods optimization procedures and lipid biomarker analyses will improve our fundamental understanding of microbial life in deep shales, and enhance our knowledge of in situ biogeochemical processes, with practical relevance to energy production after shale development.

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