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    Deuterium as a Quantitative Tracer of Enhanced Microbial Coalbed Methane Production

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    Author
    Ashley, Kilian
    Issue Date
    2017
    Keywords
    Deuterium
    MECoM
    Methane
    Natural Gas
    Stimulation
    Advisor
    McIntosh, Jennifer
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Embargo
    Release after 5-Jul-2018
    Abstract
    Microbial production of natural gas in subsurface organic-rich reservoirs (e.g. coal, shale, oil) can be enhanced by the introduction of limiting nutrients to stimulate microbial communities to generate “new” methane resources on human timescales. The few successful field experiments of Microbial Enhancement of Coalbed Methane (MECoM) relied on relatively qualitative approaches for estimating the amount of “new” methane produced during the stimulation process (i.e. extrapolation of pre-stimulation gas production curves). We have tested deuterated water as a tracer, initially in the laboratory, to more directly quantify the amount of “new” methane generated and the effectiveness of MECoM stimulation approaches. Microorganisms, formation water, and coal obtained during a previous drilling project in the Powder River Basin, Birney, Montana were used to set up a series of benchtop stimulation experiments where we added incremental amounts of deuterated water to triplicate sets of stimulated microbes (methanogens). We hypothesized that as MECoM progresses, methanogens will incorporate the heavy water into new methane produced, as methanogens naturally uptake hydrogen during methanogenesis. The amount of hydrogen incorporated into methane from water is dependent on the methanogenic pathway (hydrogenotropic vs acetoclastic/methylotrophic). During the experiments, we saw a shift in the methanogenic pathway towards acetoclastic methanogenesis, which was indicated by a consistent shift in the enrichment of deuterium in the methane produced, methanogenic community, and a large kinetic fractionation. The enrichment of the methane as compared to the deuterium content of the water the microbes used followed a narrowly confined, predictable range of values. This predictable enrichment of the methane allows us to propose a quantification scheme for the amount of methane produced in larger field scale stimulations, as we can compare the change in the overall deuterium content of the in-situ methane with the known value before the stimulation. The success of our proof-of-concept laboratory experiments suggests that deuterium may be used as a tracer of “new” natural gas resources in field- to commercial-scale MECoM projects. In addition, additions of deuterated water may also be useful as a tracer in bioremediation projects where large background pools of contaminants or degradation products hamper traditional quantification techniques, microbial enhanced oil recovery, or other subsurface carbon cycling pathways.
    Type
    text
    Electronic Thesis
    Degree Name
    M.S.
    Degree Level
    masters
    Degree Program
    Graduate College
    Hydrology
    Degree Grantor
    University of Arizona
    Collections
    Master's Theses

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