An Integrated Molecular and Isotope Approach for Estimating the Age of Crude Oils and Source-Rocks from the Beaufort-Mackenzie Basin and North Slope

Christiane Eiserbeck¹, Kliti Grice¹, Robert K. Nelson², and Joseph Curiale^3
1Applied Chemistry, Curtin University of Technology, Perth, WA, Australia.
²Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA.
³Chevron Corporation, Sugar Land, TX.

Establishing the age of a crude oil is an important tool for oil-source rock correlations. Obtaining a more precise age estimate will reduce risk in oil exploration. Therefore, the present study aims to develop a molecular and isotopic approach for high resolution age estimation of Tertiary deltaic oils and source rocks.

Stable carbon and hydrogen isotope ratios of age-diagnostic higher plant biomarkers and their distributions are being measured in crude oils and source rocks originating from the Beaufort-Mackenzie Basin and the North Slope (onshore and offshore) as well as South East Asia. The ages of the samples range from Late Palaeocene to Mid Miocene.

In order to identify and quantify higher plant biomarkers like oleanane, lupane and their diagenetically related compounds [1], several gas chromatographic systems are applied, namely gas chromatography-mass spectrometry (GC-MS) and GC-MS-MS (MRM, metastable reaction monitoring). For compound specific isotope analysis (δ¹³C and δD) a GC-irMS instrument is used.

Preliminary findings indicate the diversity and the presence of higher plant biomarkers with in part extremely depleted isotope values. The samples show a significant up to predominant terrestrial input of gymnosperm and angiosperm derived biomarkers.

Explicit identification of land plant biomarkers or exact differentiation between two isomers of a compound using GC-MS is sometimes a challenge due to co-elution and/or low abundances. For that reason, comprehensive two-dimensional GCxGC is being carried out.
Two dimensions of selectivity can be achieved by two-dimensional gas chromatography (GCxGC). It combines the separation capability of two capillary columns of different polarity. GCxGC is highly suited for the separation of complex mixtures such as petroleum [2],[3],[4].

The combined application of stable carbon and hydrogen isotopes of biomarkers and molecular characterisation of deltaic crude oils and source rocks by MRM and GCxGC will be presented for Tertiary samples from the Canadian Beaufort and South East Asia.

AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia