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CWhyte Dissertation FINAL.pdf (5.92 MB)

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Evaluating the effects of fluid migration and microbial processes on the noble gas and hydrocarbon geochemistry of shallow groundwater

Whyte, Colin James Stephen
http://rave.ohiolink.edu/etdc/view?acc_num=osu1576590616496243

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Earth Sciences.
The expansion of unconventional petroleum development enhanced production of natural gas and oil globally, but also raised concerns related to groundwater contamination resulting from drilling activities. Extensive research recently has focused on identifying contaminants (e.g., CH4, brines) related to drilling or natural processes, as well as the processes that emplace these contaminants into shallow groundwater systems. The integrated utilization of inert (e.g., noble gas), hydrocarbon (e.g., C1/C2+, compound-specific stable isotopes), and aqueous geochemical tracers has become a standard technique for identifying naturally-occurring hydrocarbon gas or brine from human-induced contamination. Still, it is often difficult to make determinations of groundwater contamination due to lack of understanding of the many processes that can alter the hydrocarbon and aqueous geochemistry following emplacement into groundwater (post-genetic modification) and a lack of baseline geochemical data. Advection, diffusion, mixing with primary microbial gas, microbial oxidation, and secondary methanogenesis can all obfuscate the geochemical characterization of a groundwater system making it essential to understand the effects of these individual processes. Here, numerical models were developed using a hypothetical thermogenic natural gas to illustrate how traditional geochemical tracers are affected by post-genetic modification following gas emplacement. The current work also examined the aqueous and gas geochemistry of groundwater samples collected from observation boreholes and residential drinking-water wells in the Saint-Edouard region of southern Quebec, Canada, and from drinking-water wells that were previously interpreted to contain fugitive gas contamination in Parker County, TX. In the Saint-Edouard region, the widespread presence of hydrocarbons in shallow groundwater and the relative lack of petroleum development provides a rare opportunity to understand naturally-occurring hydrocarbons prior to drilling and in a nearly-pristine environment. In comparison, the drinking-water wells in Parker County, TX with prior evidence of fugitive gas provides an opportunity to broaden the geochemical framework used to identify fugitive gas contamination and develop a detailed understanding of the ongoing factors that alter groundwater geochemistry in regions influenced by fugitive gas contamination. The Saint-Edouard dataset was combined with previously published stable isotopic and aqueous geochemical data, while the Parker County samples were analyzed for a suite of inorganic and stable isotopic tracers and major gas ratios in addition to more traditional geochemical tracers. Both datasets suggest microbial oxidation of thermogenic hydrocarbons is occurring in these regions, while positive trends in δ13C-DIC, [HCO3], and negative δ13C-CH4 may indicate secondary methanogenesis. In the Saint-Edouard region, the absolute and relative abundances of noble gas isotopes suggest groundwater degassing, perhaps as the result of the addition of secondary microbial CH4. In Parker County, TX, the generation of H2S following sulfate-paired oxidation of fugitive hydrocarbons enhances the potential environmental and health risks associated with fugitive gas contamination. In combination, the numerical models for post-genetic modification and groundwater geochemical data from areas with natural and anthropogenic hydrocarbon contamination provide insight into the evolution of hydrocarbons in shallow groundwater.
Thomas Darrah, Ph.D. (Advisor)
Franklin Schwartz, Ph.D. (Committee Member)
W. Berry Lyons, Ph.D. (Committee Member)
Michael Barton, Ph.D. (Committee Member)
182 p.
Geochemistry
hydrocarbons, post-genetic modification, isotope fractionation, oxidation, methanogenesis

Recommended Citations

Citations

  • Whyte, C. J. S. (2020). Evaluating the effects of fluid migration and microbial processes on the noble gas and hydrocarbon geochemistry of shallow groundwater [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1576590616496243

    APA Style (7th edition)

  • Whyte, Colin. Evaluating the effects of fluid migration and microbial processes on the noble gas and hydrocarbon geochemistry of shallow groundwater. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1576590616496243.

    MLA Style (8th edition)

  • Whyte, Colin. "Evaluating the effects of fluid migration and microbial processes on the noble gas and hydrocarbon geochemistry of shallow groundwater." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1576590616496243

    Chicago Manual of Style (17th edition)

osu1576590616496243
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This open access ETD is published by The Ohio State University and OhioLINK.
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