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TitleStratigraphy, age, and petroleum potential of Upper Devonian black shale (unit 'Cf'), east Richardson Mountains and Peel Plateau, Yukon
AuthorAllen, T L; Fraser, T A; Hutchison, M P; Dolby, G; Reyes, JORCID logo; Utting, J
SourceYukon Geological Survey Open File 2015-3, 2015, 55 pages Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130341
PublisherYukon Energy, Mines and Resources
Documentopen file
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®)
ProgramGEM: Geo-mapping for Energy and Minerals Yukon Sedimentary Basins
Released2015 01 01
AbstractPeel Plateau and the contiguous east flank of the Richardson Mountains, northeastern Yukon, comprise a relatively unexplored but prospective petroleum basin. Within the Devonian succession of this basin, shale rocks of unit 'Cf' (Norris, 1981a) are little known, but may have the potential to form an important conventional source and/or unconventional reservoir target. Unit 'Cf' is dominated by thick intervals of dark grey to black, siliceous, organic-rich marine shale, together with intercalated siltstone and very fine grained sandstone beds. Although unit 'Cf' has been mapped at surface on the eastern flank of the Richardson Mountains, it is not known whether it occurs to the east in the Peel Plateau and Plain subsurface. A correlation of this unit to the Ford Lake Shale ('CF' map unit of Norris, 1981b,c), which occurs to the west in Eagle Plain and Kandik basins, has been implied by the nomenclature used by Norris (1981b, 1985a).
In this study, unit 'Cf' was assessed for lithology, mineralogy, age and hydrocarbon source and reservoir rock potential, including type and quantity of organic matter and thermal maturity. Common organic geochemical analytical techniques were utilized (including Rock-Eval pyrolysis and optical microscopy), together with X-ray diffraction (XRD) to determine shale mineralogy and age determination by palynology. Outcrop characteristics were then utilized to identify unit 'Cf' in four subsurface Yukon wells: H-37, N-25, I-21 and A-42.
Results have demonstrated the potential of unit 'Cf' shale as both source rocks and shale oil/gas reservoirs, and suggest that these strata have been overlooked as a hydrocarbon target in Yukon's Peel region. Rock-Eval results indicate that organic matter in unit 'Cf' consists of mixtures of type II and III kerogen (oil to gas-prone), and organic petrology confirms this in addition to the presence of type I kerogen (oil-prone). Organic matter is identified as mainly amorphous kerogen with alginite, vitrinite, and liptinite. The classification of unit 'Cf' as a good to very good source rock that has good to very good hydrocarbon generation potential is derived from: TOC contents ranging from 1.02-12.17 wt% (averaging 5.28 wt%), average S1 values of 1.61 mg HC/g rock and average S2 values of 12.91 mg HC/g rock. Thermal maturity indicators also place unit 'Cf' shale in the 'oil-window', or early stage of thermal diagenesis, including Tmax values between 423° and 444°C, and vitrinite reflectance values between 0.5 and 0.95% RoR. Reddened shale (or clinker) units observed in the region attest to the high TOCs in these strata, and are evidence of historical and/or current burning. XRD results demonstrate the high silica (typically in excess of 90% quartz) and low clay mineral (<7%) contents of these strata, suggesting their ability to respond to artificial well stimulation techniques for unconventional hydrocarbon production.
A combination of palynological age (Fammenian-Late Devonian), TOC content (>1.02 wt%) and lithological composition data derived from outcrop results were utilized to successfully identify unit 'Cf' in the subsurface. Comparable strata were identified predominantly from within the Tuttle Formation, where their stratigraphic character changed from being present as two discrete, silt-rich, thin (95 m) intervals in the northwest (Caribou N-25) to one, shale-prone, thick (1118 m) interval in the southeast (Peel River I-21). Further work is planned to delineate the unit's regional extent in the subsurface, and to establish a correlative stratigraphic framework with the Ford Lake Shale in Eagle Plain and Kandik basins to the west.
Summary(Plain Language Summary, not published)
In this study, Upper Devonian rock unit known as "Cf", that occurs widely along the eastern flank of the south Richardson Mountains and adjoining Peel Plateau area, northeast Canada, was assessed for its lithology, geological age and petroleum source rock potential. This rock contains thick intervals of dark grey to black shale, with intercalated siltstone and very fine-grained sandstone beds. Common analytical techniques, such as X-ray diffraction, optical microscopy and palynological and organic geochemical analyses, were used. The results indicate the rock is highly siliceous containing over 92% quartz and less than 5% clay minerals. The age of the studied strata was determined as Famennian (Late Devonian). The organic matter content varies from 1.02% to 12.17% of the total weight (average of 5.28%). Other organic petrological and geochemical data suggest that this rock has good potential as source of hydrocarbons and have reached an early-mid stage of petroleum generation.

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