D/H ratios in terrestrially sourced petroleum systems

Arndt Schimmelmann*, Alex L. Sessions, Christopher J. Boreham, Dianne S. Edwards, Graham A. Logan, Roger E. Summons

*Corresponding author for this work

    Research output: Contribution to journalArticle

    67 Citations (Scopus)

    Abstract

    D/H ratios of terrestrially-sourced whole oils and their respective saturated, aromatic, and polar fractions, individual n-alkanes, formation waters and non-exchangeable hydrogen in kerogen were measured in potential source rocks from seven Australian petroleum basins. Data for 75 oils and condensates, their sub-fractions and 52 kerogens indicate that oil sub-fractions have δD values comparable to δDoil, with a ΔδD offset (δDkerogen-δDoil) averaging ca. 23‰. The weighted-average δD of individual n-alkanes is usually identical to δDoil and δDsaturate. A trend of increasing δD with n-alkane chain length in most oils causes individual n-alkanes from an oil to vary in δD by 30‰ or more. A modest correlation between δD for aromatic sub-fractions and formation waters indicates that about 50% of aromatic C-bound H has exchanged with water. In contrast, δDoil and δDsaturated show no evidence for H-exchange with formation water under reservoir conditions at temperatures up to 150°C. Acyclic isoprenoids and n-alkanes show essentially indistinguishable δD, indicating that primary isotopic differences from biosynthesis have been erased. Overall, extensive exchange of C-bound H in petroleum with other hydrogen is apparent, but seems to have affected most hydrocarbons only during their chemical genesis from precursor molecules. Our isotopic findings from terrestrially-sourced oils should be qualitatively relevant for marine oils as well.

    Original languageEnglish
    Pages (from-to)1169-1195
    Number of pages27
    JournalOrganic Geochemistry
    Volume35
    Issue number10
    DOIs
    Publication statusPublished - Oct 2004

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