Molecular Evolution of Sedimentary Organic Matter in Marcellus Shale.

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Several biological and physico-chemical processes lead to the transformation of organic matter (OM) from simple organic compounds to a complex macromolecule and a mixture of hydrocarbons during the geological evolution of sedimentary rocks. These changes are controlled by biological activity in the early stages of burial, and by temperature and pressure in the later stages. The increasing temperature and pressure conditions with burial is termed as maturation, in which biomolecules are converted into petroleum. Three consecutive stages of maturation namely: diagenesis, catagenesis and metagenesis produce irreversible changes in the composition of sedimentary OM. The bulk characteristics (such as elemental composition) of OM starting from its deposition to the formation of oil and gas are well understood in the past using traditional methods such as source rock analyzer (SRA). However, a large knowledge gap still exists in understanding the processes involved in the transformation and evolution of OM during maturation at the molecular level. Understanding the molecular level properties of shale OM is important for precise estimation of hydrocarbons, increasing efficiency of HC recovery and production, designing effective CO2 sequestration and waste disposal strategies, and understanding mechanisms of contaminant release and sorption. The primary objective of my PhD dissertation is to understand evolution of sedimentary OM at molecular scale in Marcellus Shale. The Marcellus Shale is the largest natural gas producing reservoir in the United States and has been extensively drilled in the past decade. The amount of natural gas extracted from the reservoir has almost tripled due to advancements in horizontal 3 drilling technologies. As a result, thousands of wells have been drilled in areas of Pennsylvania, Ohio and West Virginia covering a wide range of maturation (from early oil window to overmature window) and paleo-depositional environments. Drilling of these wells provides access to several thousand feet deep core samples for biogeochemical analysis. In my study, I utilized core samples of Marcellus shale with variable maturity (ranging from 0.8 VRo to 3 VRo) and depositional environment. The variability in sources of OM, paleo-redox conditions and thermal maturation was determined using pyrolysis and biomarker proxies especially in samples from mature part of the basin. Once the information about source of OM and maturation was established, kerogen was extracted from the Marcellus Shale maturity series. Chemical composition and structural properties of the extracted kerogen was determined using advanced spectroscopic techniques. Using the distribution and changes in structural parameters of kerogen, an understanding