D/H ratios in terrestrially sourced petroleum systems

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 dD values comparable to dDoil, with a DdD offset (dDkerogen dDoil) averaging ca. 23‰. The weighted-average dD of individual n-alkanes is usually identical to dDoil and dDsaturate. A trend of increasing dD with nalkane chain length in most oils causes individual n-alkanes from an oil to vary in dD by 30‰ or more. A modest correlation between dD for aromatic sub-fractions and formation waters indicates that about 50% of aromatic C-bound H has exchanged with water. In contrast, dDoil and dDsaturated 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 dD, 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. 2004 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +1-812-855-7645; fax: +1-812855-7961. E-mail addresses: aschimme@indiana.edu (A. Schimmelmann), als@gps.caltech.edu (A.L. Sessions), chris.boreham@ ga.gov.au (C.J. Boreham), dianne.edwards@ga.gov.au (D.S. Edwards), graham.logan@ga.gov.au (G.A. Logan), rsummons@mit.edu (R.E. Summons). 1 Current address: California Institute of Technology, Division of Geological and Planetary Sciences, Mail Code 100-23, Pasadena, CA 91125, USA. 0146-6380/$ see front matter 2004 Elsevier Ltd. All rights reserv doi:10.1016/j.orggeochem.2004.05.006

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Cite this paper

@inproceedings{Schimmelmann2004DHRI, title={D/H ratios in terrestrially sourced petroleum systems}, author={Arndt Schimmelmann and Alex L Sessions and Christopher J. Boreham and Dianne S. Edwards and Graham A. Logan and Roger E Summons}, year={2004} }