Intramolecular 13C isotope distributions of butane from natural gases

Maxime Julien, Mark J. Goldman, Changjie Liu, Juske Horita, Christopher J. Boreham, Keita Yamada, William H. Green, Naohiro Yoshida, Alexis Gilbert

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7 Scopus citations

Abstract

A single-step method allowing the measurement of 13C intramolecular distribution of butane isomers (n- and i-butane) from natural gas samples was developed. The method builds up on the one that has been developed for propane, using on-line pyrolysis followed by isotope analysis of the pyrolytic fragments. The isotopic filiation between n-butane and its pyrolytic fragments was elucidated using samples spiked with 13C on terminal positions. The isotopic filiation for i-butane could not be shown experimentally due to the lack of commercially available enriched i-butane. We thus used a recent model named Reaction Mechanism Generator (RMG) to assess the origin of the fragments arising from i-butane pyrolysis. Butanes from natural gas samples from the Carnarvon Basin (Australia) and the Arkoma Basin (USA) were analyzed. The results are consistent with a model for thermogenic natural gas generation and suggest that combined intramolecular isotope composition of propane and n-butane can be related to the gas maturity. In addition, the method allows the detection and shed light on the mechanism of n-butane and i-butane biodegradation in natural gas reservoirs.

Original languageEnglish
Article number119571
JournalChemical Geology
Volume541
DOIs
StatePublished - May 20 2020

Keywords

  • Butane isomers
  • Carbon isotopes
  • Hydrocarbons
  • Intramolecular isotope
  • Natural gas

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