Abstract

Triassic strata in the Western Canada Sedimentary Basin contain significant quantities of petroleum. Potential sources for these hydrocarbons are known for many, but not all, of the Triassic petroleum accumulations. This study documents the geochemistry of potential hydrocarbon source rock intervals from outcrops of the Vega-Phroso. Whistler and Llama members of the Sulphur Mountain Formation and the Grayling, Toad and Pardonet formations. Total organic carbon contents range up to 15 wt.% for these units, which contain Type II marine kerogen. The biomarker compositions of rock extracts from Lower and Middle Triassic, thermally mature, outcrop formations are similar in many respects; however it is suggested that a number of ratios (e.g., pristane/phytane, C 27 diasterane/regular sterane, C 27 /C 28 sterane ratios) may be used to distinguish oils from these various sources. It is anticipated that these biomarker data will provide the basis for correlation to oils preserved in regions which are presently overmature with respect to hydrocarbon generation. A revised thermal maturity map for the Triassic is presented, based on new thermal maturity data from the subsurface of British Columbia. These new data indicate anomalous heat flow associated with the Hay River Fault Zone, a basement feature which trends northeast-southwest and extends from northeastern British Columbia to the Northwest Territories. The results presented here have significant implications for hydrocarbon exploration in northeastern British Columbia and west-central Alberta. The occurrence of mature, oil-prone source rocks in regions considered prospective only for dry gas suggests new areas with liquid hydrocarbon potential. The existence and discovery of such hydrocarbon occurrences will require integration of the data presented here with knowledge of the structure, reservoir units, seal rocks and timing of hydrocarbon generation and migration relative to trap formation in the area immediately east of the outcrop belt. This study also documents hydrocarbon source rock potential in Lower Triassic strata at outcrop. These oil-prone intervals are also believed to occur in subsurface regions to the east of the Foothills Belt and have likely provided the source for local oil accumulations in Lower Triassic strata. Stratigraphic studies, using sequence stratigraphic analysis, are currently in progress, with a view to predict the lateral distribution of these organic-rich intervals into sparsely explored regions. Finally, it is suggested that the organic-rich Pardonet Formation in northeastern British Columbia may represent a prospective fractured shale play in the Western Canada Sedimentary Basin.

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