Abstract

Numerous gas and oil fields are hosted in the Baldonnel and Pardonet formations of northeastern British Columbia, Canada. The source of the hydrocarbons in these fields has not been demonstrated using organic geochemical methods. However lithologic characteristics, interpreted depositional settings, and some published organic carbon content values have led to speculation that Upper Triassic strata of northeastern British Columbia, in particular the Pardonet Formation, may include important hydrocarbon source rocks.

In order to assess the hydrocarbon source rock potential of Upper Triassic strata in northeastern British Columbia, nine outcrops and seven drillcores were measured, described and sampled for geochemical analyses. Geochemical analyses using Rock-Eval/TOC pyrolysis indicate a total organic carbon (TOC) content ranging from 0.03 to 2.08 weight percent for the Baldonnel (majority <1.0 wt %) and 0 to 4.8 weight percent for the Pardonet Formation samples. Rock-Eval Tmax data indicate that Upper Triassic strata are late mature to overmature with respect to liquid hydrocarbon generation at the studied localities. One exception is the West Burnt River outcrop location (55°20′N; 122°20′W), where the Pardonet Formation is at early peak hydrocarbon maturity (Tmax=437°C), with Hydrogen Index values from 170 to 315 mg HC/g TOC, indicating Type II (oil-prone) kerogen. However, West Burnt River TOC values (0.6 to 1.4 wt %) are not as high as those observed at other outcrop localities and in core, possibly due to lateral facies variations, or to sampling bias (i.e., these samples are from the GSC Archives, and were not collected by the authors).

Geochemical data from outcrop and core suggest that the Pardonet Formation in northeastern B.C. had good to very good initial hydrocarbon potential, and has generated economically significant quantities of hydrocarbon. However, gas isotopic and gas compositional data, as well as biomarker analysis of oils and source rock extracts, are required to demonstrate whether the Pardonet, or some other, deeper unit, was the source of hydrocarbons found in Upper Triassic reservoirs in northeastern B.C. Mass balance calculations based on the geochemical data presented here for the Pardonet Formation, suggest that current initial in-place reserve estimates for Upper Triassic reservoir strata are four to five times less than expected. We speculate that some proportion of this calculated volume of hydrocarbons may have been retained within the Pardonet Formation itself, suggesting some potential as a fractured shale play. The Baldonnel Formation had only poor to fair initial hydrocarbon potential, and was not a significant hydrocarbon source.

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