Oil-source and oil-oil correlations and the origin of the heavy oil and bitumen accumulations in Northern Alberta, Canada

Abstract

The saturated and aromatic hydrocarbon compositions of potential source rock samples from the Devonian/Carboniferous Duvernay, Exshaw, and Lower Banff formations, the Triassic Doig Formation, and the Jurassic Gordondale (Nordegg) and Poker Chip Shale formations in the Western Canada Sedimentary Basin (WCSB) were investigated by gas chromatography–mass spectrometry (GC–MS). The study also included produced oils from the Cretaceous Clearwater play at Marten Hills and Peace River, oil sands cores from Athabasca and Cold Lake areas, and bitumen hosted in the Grosmont carbonate deposits.Oil-oil and oil-source correlation based on the aromatic steroid hydrocarbon compounds is enabled by their strong resistance to biodegradation and their presence in all reservoir samples analyzed. In addition, of the aromatic steroids hydrocarbons, triaromatic-dimethylcholesteroids (TA-DMC) and triaromatic dinosteroids represent age-diagnostic biomarkers that distinguish Paleozoic versus Jurassic sources. The Duvernay, Exshaw, and Lower Banff extracts lack TA-DMC and triaromatic dinosteroids, whereas extracts from the Gordondale and Poker Chip Shale display appreciable quantities of TA-DMC and triaromatic dinosteroids. Meanwhile, the Doig falls between the Gordondale/Poker Chip Shale and Duvernay/Exshaw source types in terms of the distribution of these triaromatic steroids. The compositions of TA-DMC and triaromatic dinosteroids in the oil sands and Grosmont bitumen are remarkably similar, confirming that these oil deposits are genetically related. The aromatic steroid hydrocarbon compositions of the oil sands and Grosmont bitumen most strongly resemble those for the Gordondale and Poker Chip Shale. Saturated biomarker features of the oil sands and Grosmont carbonate bitumen including 28,30-bisnorhopane and high diasteranes relative to regular steranes, although lacking in the Gordondale extracts, may be introduced through mixing with oil generated from the Poker Chip Shale. However, plots based on aromatic steroids and source-specific biomarkers such as aryl and diaryl isoprenoids indicate some degree of mixing with Duvernay and/or Exshaw contributions. This is also supported by a mixing model employing the averaged concentrations of methyltriaromatic steroids from endmember Gordondale and Exshaw extracts. These findings along with additional biomarker evidence support a strong Jurassic contribution to the studied oil sands and call for re-evaluation of the petroleum systematics of the WCSB.