Comparison of isotopic compositions of hydrocarbon gas in shallow groundwater and a deep oil and natural gas reservoir in southeastern New Brunswick, Canada

Authors

  • Diana B. Loomer Department of Civil Engineering, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
  • Kerry T.B. MacQuarrie Department of Civil Engineering, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
  • Tom A. Al Department of Earth and Environmental Science, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

DOI:

https://doi.org/10.4138/atlgeol.2020.009

Abstract

Isotopic analyses of natural gas from the Stoney Creek oil field in New Brunswick indicate carbon (δ13C) and hydrogen (δ2H) values in methane (C1) of -42.4 ± 0.7‰ VPDB and -220.9 ± 3.2‰ VSMOW, respectively. Isotopic data and a gas molecular ratio of 12 ± 1 indicate a wet thermogenic gas formed with oil near the onset of the oil-gas transition zone. The isotopic profiles of the C1–C5 hydrocarbon gases are consistent with kinetic isotope effect models. The Albert Formation of the Horton Group hosts the Stoney Creek oil field (SCOF) and the McCully gas field (MCGF) the only other gas-producing field in the province. Both are thermogenic in origin; however, the SCOF gas has a lower thermal maturity than the MCGS. Hydrocarbon gas composition in shallow aquifers across southeastern New Brunswick was also evaluated. Gas source interpretations based on δ13C and δ2H values are uncertain; oxidation and biogenic overprinting are common and complicate interpretation. The effect of oxidation on δ13C and δ2H values was apparent when C1 concentrations were ≤1 mg/L. In some samples with C1 concentrations >5 mg/L, isotopic discrimination methods point to a biogenic origin. However, the molecular ratios <75 and the presence of >C3 fractions, indicate a thermogenic origin. This suggests a thermogenic isotopic signature has been overprinted by biological activity.

Downloads

Published

2020-10-03

How to Cite

Loomer, D. B., MacQuarrie, K. T., & Al, T. A. (2020). Comparison of isotopic compositions of hydrocarbon gas in shallow groundwater and a deep oil and natural gas reservoir in southeastern New Brunswick, Canada. Atlantic Geoscience, 56, 207–229. https://doi.org/10.4138/atlgeol.2020.009

Issue

Vol. 56 (2020)

Section

Articles

License

All material contained in Atlantic Geology is copyrighted by the journal. Permission to photocopy for internal or personal use or for the internal or personal use of specific clients is granted by Atlantic Geology to libraries and other users registered with the Copyright Clearance Center (CCC), provided that the stated fee per copy is paid directly to the CCC, 21 Congress Street, Salem, Massachusetts 01970 USA. Other requests should be addressed to one of the journal editors, or sent to Atlantic Geology, Box 116, Acadia University, Wolfville, NS, Canada B4P 2R6. Permission to use a single graphic for which Atlantic Geology owns copyright is considered “fair dealing” under the Canadian Copyright Act and “fair use” by the journal, and no other permission need be granted, subject to the image being appropriately cited in all reproductions. The same fair dealing/fair use policy applies to sections of text up to 100 words in length.