ABSTRACT

The organic geochemical potential of six actual to potential source intervals from the Western Canada Basin (WCB) has been assessed by Rock-Eval pyrolysis and saturate and aromatic fraction biomarker geochemistry. Intervals studied include Second White Specks and Fish Scales (Upper Cretaceous), "Nordegg" (Jurassic), Doig (Triassic), Exshaw (Devonian/Mississippian), and Duvernay (Devonian). Second White Specks TOC values range from 2 to 12 per cent; Tmax and hydrogen index (HI)-based maturity ranges from immature to mature toward the west. Biomarker parameters including regular sterane distributions are distinctive: oils above the Viking Formation clearly correlate with this unit. "Nordegg" samples are distinguished by distributions of steroidal alkanes, Tx/Tm ratios and rear-ranged to regular sterane ratios, as are two Peace River Arch (PRA) area oils recognized to date from this unit. Doig samples from PRA area are mature to overmature and have TOC values from 2 to 11 per cent: most extracts and associated oils have abundant tricyclic terpanes relative to pentacyclic terpanes, and high Ts/Tm ratios. Duvernay TOC's from basin-centred samples range from 4 to 13 per cent; samples are moderately mature based on Tmax and HI values. Unique patterns of triaromatic steranes and the virtual absence of C₃₀ desmethyl steranes allow Duvernay samples and derived oils to be distinguished from other WCB oils. Exshaw samples from PRA and more central parts of the basin resemble Duvernay samples in TOC, maturity level and biomarker distributions. None of these actual and potential source rocks have the specific geochemical characteristics of the enormous accumulations of Paleozoic and Mesozoic tar sands and heavy oils.

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