Print this pagePolar heterocompounds in 
oil
-source rock correlation
studies
Christian Hallmann, Geological Institute,
The purpose of this study is to monitor carbazole distributions in oils,
source rock extracts and source rock pyrolysates in order to establish a
molecular marker in the polar petroleum fraction, indicative for source facies.
The Cooper/Eromanga Basins, oil and gas
condensates that were sourced by at least three discrete terrestrial source
rocks. Their highly similar source facies precludes a detailed oil-source rock
correlation. Jurassic-sourced oils can be discriminated from Paleozoic-sourced
oils by aromatic hydrocarbon biomarkers that were produced exclusively by
post-Triassic Araucariacea conifers. Preliminary results indicate that
distribution patterns of nitrogen-containing carbazole compounds allow a
precise discrimination of all three source rock units (Jurassic/Permian/pre-Permian)
present in the study area.
We plan to subject immature, unaltered source rock
samples from all three aforementioned source units to hydrous pyrolysis.
Pyrolysates will be analysed for carbazole and hydrocarbon biomarker
compositions by molecular geochemistry. Molecular compositions of hydrous
pyrolysates are comparable to those of naturally generated oils. Pyrolysates,
however, are unaffected by secondary alteration and oil mixing processes. Thus
they should exhibit pristine end-member oil compositions. If the molecular
composition of source rock pyrolysates supports our earlier observations, we
can provide a powerful new tool for correlating oils and source rocks based on
heterocompound compositions.
The anticipated results will not only enhance our
understanding of the Cooper/Eromanga Basin oil play, but also aid in future
exploration activities, elsewhere. Furthermore, the finding of facies-dependent
markers in polar petroleum fractions is a positive motivation for further
research into the geochemistry of petroleum heterocompounds.
