Organic geochemistry and organic petrology of a potential source rock of early Eocene age in the Beaufort–Mackenzie Basin

The biological marker compounds 17α(H) and 17β(H), 23,28-bisnorlupane have been identified in a coaly interval at about 3300–3320 m depth within the lower Taglu Sequence (early Eocene) in the Immiugak A-06 well in the Beaufort–Mackenzie Basin. These biomarkers were previously only known to occur in the lower part of the Richards Formation and were thus used to infer that the Richards was the source for most of the Tertiary oils and condensates in the basin. The discovery of bisnorlupanes in older, much more organic-rich rocks indicates that the previous oil–source rock correlations may not have been correct and that the coals in the lower Taglu Sequence are likely the dominant effective source rock, especially for the Paleocene and early Eocene reservoirs in the southern part of the Mackenzie Delta. Petrographic and Rock–Eval analyses indicate that the lower Taglu Sequence coaly section should be mainly a source for gas, but with some potential to expel liquids. The level of thermal maturity inferred from Rock–Eval Tmax (432–438 °C, equivalent to about 0.65–0.75% Ro vitrinite) is slightly higher than that inferred from the measured reflectance, fluorescence and foraminiferal colouration index which all indicate that the maturity at 3300 m is about 0.60–0.65% Ro vitrinite equivalent at the Gulf et al. Immiugak A-06 well site.