Energy in Canada's North

Devonian Shale Basin Characterization in the Central Northwest Territories – Results of Outcrop Sampling

Tuesday, November 19, 2019 - 8:20am to 8:40am Theatre Three


V. Terlaky (Presenting)
Northwest Territories Geological Survey
K.M. Fiess
Northwest Territories Geological Survey
J. Rocheleau
Northwest Territories Geological Survey

In 2014, the Northwest Territories Geological Survey (NTGS) continued the source-rock characterization studies of Devonian black shales, including the Bluefish Member of the Hare Indian Formation and the Canol Formation. As part of the ongoing Shale Basin Evolution Project, the NTGS sampled six outcrops during the summers of 2016 and 2018 – which in a southeast-northwest transect include Carcajou River, Dodo Canyon, Powell Creek, Arctic Red River East, Rumbly Creek, and Flyaway Creek. The study included strategically selected outcrops and stratal intervals in order to fill areal and stratal data gaps in the regional dataset. This work resulted in the creation of a detailed regional dataset covering the Devonian Horn River Group in the Central Mackenzie Valley and southern Peel Plain and Peel Plateau areas of the Northwest Territories (NWT). Here, the scientific results from the 2016 and 2018 summer field seasons are highlighted. These data, then, are combined with legacy data from several outcrops and industry cores and put into regional context.

The data suggest that the Bluefish Member comprises organic-rich shales with generally good, but regionally variable total organic carbon (TOC) content, also indicated by consistently high uranium concentration. Silica content in the Bluefish Member is moderate and variable, resulting in lower brittleness of the rock, which was also observed in the field. Terrestrial input, based on geochemical indicators, is generally low for the Bluefish Member, but increases upward in stratigraphy. Palaeoredox indicators suggest deposition under at least partly anoxic conditions. The Bell Creek member has generally low TOC content and low uranium concentration. Silica content is also low with an elevated terrestrial input signature. Palaeoredox indicators suggest sustained oxic conditions. The Canol Formation has a variable but generally elevated TOC content. Silica content in the Canol Formation is the highest of these formations, resulting in brittle fracturing noted in the field. Terrigenous input is low through Canol Formation deposition. Palaeoredox indicators suggest variable conditions during deposition.

Source-rock and vitrinite reflectance analyses indicate a regionally variable trend of rock maturity, with an abrupt increase in maturity toward the western part of the study area. In the eastern locations (Carcajou River, Dodo Canyon, and Powell Creek), production index (PI), vitrinite reflectance (VR) and Tmax values are in agreement, indicating maturity in the oil window. In the western outcrops, however, PI and Tmax values are not in agreement; PI values indicate oil window maturity, whereas Tmax values indicate overmaturity. The VR for these outcrops resulted in poor data quality. This trend in the western locations may be the result of expulsion and pyrolyzation of inert residual carbon.

Conodont and stable isotope analysis results from Arctic Red River East are complimentary and are used to elucidate the chronostratigraphy of these strata. The results are correlated to the global δ13Ccarb reference curve and conodont biozones, resulting in a high-resolution chronostratigraphic framework for the Horn River Group at this location. Collectively, these results will be used in the on-going basin modelling efforts of the NTGS.