Subsurface Carbocation Processes Revealed by a Stable Isotopic Study of the Aromatic UCM

The unresolved complex mixture (UCM) is a feature most prominent in gas chromatograms of biodegraded samples. In a recent study, the mono-, di- and triaromatic fractions were separated from the UCM of a crude oil (Leatherjacket-1, Gippsland Basin, Australia) and subjected to ruthenium tetroxide oxidation to yield carboxylic acids as alkyl side chains. Deuterium labelling was used to identify the positions of carboxylic acid moieties on the aromatic ring present in the original unoxidised fraction. The saturated hydrocarbons from the mono-, di- and triaromatic fractions were 60%, 60% and 75% GC-resolved respectively (cf. 12% for the initial aromatic fraction). d13C for the n-alkanes (from C8 to C29) released from all three fractions were similar, showing an isotope profile comparable to a non-biodegraded oil sourced from the same basin.

Personnel

B. Warton, K. Grice, R. Alexander, R. Kagi

Funding

Centre of Excellence in Mass Spectrometry