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Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study.

Publication ,  Journal Article
Eymold, WK; Swana, K; Moore, MT; Whyte, CJ; Harkness, JS; Talma, S; Murray, R; Moortgat, JB; Miller, J; Vengosh, A; Darrah, TH
Published in: Ground water
March 2018

Horizontal drilling and hydraulic fracturing have enhanced unconventional hydrocarbon recovery but raised environmental concerns related to water quality. Because most basins targeted for shale-gas development in the USA have histories of both active and legacy petroleum extraction, confusion about the hydrogeological context of naturally occurring methane in shallow aquifers overlying shales remains. The Karoo Basin, located in South Africa, provides a near-pristine setting to evaluate these processes, without a history of conventional or unconventional energy extraction. We conducted a comprehensive pre-industrial evaluation of water quality and gas geochemistry in 22 groundwater samples across the Karoo Basin, including dissolved ions, water isotopes, hydrocarbon molecular and isotopic composition, and noble gases. Methane-rich samples were associated with high-salinity, NaCl-type groundwater and elevated levels of ethane, 4 He, and other noble gases produced by radioactive decay. This endmember displayed less negative δ13 C-CH4 and evidence of mixing between thermogenic natural gases and hydrogenotrophic methane. Atmospheric noble gases in the methane-rich samples record a history of fractionation during gas-phase migration from source rocks to shallow aquifers. Conversely, methane-poor samples have a paucity of ethane and 4 He, near saturation levels of atmospheric noble gases, and more negative δ13 C-CH4 ; methane in these samples is biogenic and produced by a mixture of hydrogenotrophic and acetoclastic sources. These geochemical observations are consistent with other basins targeted for unconventional energy extraction in the USA and contribute to a growing data base of naturally occurring methane in shallow aquifers globally, which provide a framework for evaluating environmental concerns related to unconventional energy development (e.g., stray gas).

Duke Scholars

Published In

Ground water

DOI

EISSN

1745-6584

ISSN

0017-467X

Publication Date

March 2018

Volume

56

Issue

2

Start / End Page

204 / 224

Related Subject Headings

  • Water Pollutants, Chemical
  • Oil and Gas Fields
  • Natural Gas
  • Methane
  • Hydrocarbons
  • Groundwater
  • Environmental Monitoring
  • Environmental Engineering
  • 3709 Physical geography and environmental geoscience
  • 3707 Hydrology
 

Citation

APA
Chicago
ICMJE
MLA
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Eymold, W. K., Swana, K., Moore, M. T., Whyte, C. J., Harkness, J. S., Talma, S., … Darrah, T. H. (2018). Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study. Ground Water, 56(2), 204–224. https://doi.org/10.1111/gwat.12637
Eymold, William K., Kelley Swana, Myles T. Moore, Colin J. Whyte, Jennifer S. Harkness, Siep Talma, Ricky Murray, et al. “Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study.Ground Water 56, no. 2 (March 2018): 204–24. https://doi.org/10.1111/gwat.12637.
Eymold WK, Swana K, Moore MT, Whyte CJ, Harkness JS, Talma S, et al. Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study. Ground water. 2018 Mar;56(2):204–24.
Eymold, William K., et al. “Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study.Ground Water, vol. 56, no. 2, Mar. 2018, pp. 204–24. Epmc, doi:10.1111/gwat.12637.
Eymold WK, Swana K, Moore MT, Whyte CJ, Harkness JS, Talma S, Murray R, Moortgat JB, Miller J, Vengosh A, Darrah TH. Hydrocarbon-Rich Groundwater above Shale-Gas Formations: A Karoo Basin Case Study. Ground water. 2018 Mar;56(2):204–224.
Journal cover image

Published In

Ground water

DOI

EISSN

1745-6584

ISSN

0017-467X

Publication Date

March 2018

Volume

56

Issue

2

Start / End Page

204 / 224

Related Subject Headings

  • Water Pollutants, Chemical
  • Oil and Gas Fields
  • Natural Gas
  • Methane
  • Hydrocarbons
  • Groundwater
  • Environmental Monitoring
  • Environmental Engineering
  • 3709 Physical geography and environmental geoscience
  • 3707 Hydrology