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This study presents the first shale gas appraisal of Devonian-Mississippian shale strata in Yukon’s Liard basin. Assessed volumes of 68 Tcf gas-in-place and 7.6 Tcf marketable gas are contained within two shale plays identified from an integrated wireline log and geochemical evaluation: the Devonian (Givetian-Frasnian) Horn River shale and the Devonian-Mississippian (Famennian-Tournaisian) Exshaw-Patry shale. Average burial depths of 3018 mTVD and net pay thicknesses of 73 m for the Horn River, and 2688 mTVD and 89 m for the Exshaw-Patry plays are interpreted. Both plays are dominated by black, organic-rich, siliceous mudstones, and exhibit: elevated TOC contents (0.6-6.9 wt %); maturities within or past the dry gas window (2.1-4.6 %Ro); very high biogenic silica proportions (averaging 80.2-90.3%); high mineralogical stiffness (0.80-0.87); and average porosities of 1.2% for the Horn River and 4.2% for the Exshaw-Patry play. Resource distribution models indicate 50% of Yukon’s marketable gas will be found in 30% of its assessed area, with the best potential for significant volumes located in the very southeast of the territory where play depth and thickness increases.

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Peel 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’ 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), which occurs to the west in Eagle Plain and Kandik basins, has been implied. 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.

An evaluation of hydrocarbon resource potential in Eagle Plain is one aspect of the Yukon Sedimentary Basins Project, a five-year (2008-2013), collaborative Geo-Mapping for Energy and Minerals (GEM) Program of the Geological Survey of Canada (GSC), in partnership with the territorial governments and universities. As part of this project, Yukon Geological Survey (YGS) and Northern Cross (Yukon) Limited (NCY) are collaborating with the GSC to assess shale gas potential of Devonian shale at Eagle Plain. Diamond drill core was retrieved from mineral exploration properties to evaluate shale gas potential of Devonian shale of Road River Group and Canol and Imperial formations. Diamond drill core from four holes, located on the Rich property east of Eagle Plain Hotel, were examined and sampled. The core was systematically sampled and analysed by Rock-Eval pyrolysis, optical microscopy, X-ray diffraction (XRD) mineralogy, and palynology. The results indicate that the succession is thermally overmature with respect to hydrocarbon generation. Due to the high levels of thermal maturity, the Rock-Eval data are unreliable. However, high amounts of residual organic carbon suggest that the Canol Formation has the potential to be an important source rock in the region, under favourable burial conditions. The very high level of thermal maturity of the strata also resulted in very few identifiable Palynomorphs; however, Canol and Imperial formation samples yielded dates of Middle to Late Devonian and Frasnian to Famennian, respectively. XRD analyses indicate Canol Formation shale is highly siliceous whereas Road River Group shale and silty shale of the Imperial Formation are less siliceous and exhibit a more varied lithology. This study suggests that the Canol Formation is more prospective for shale gas than strata of the Imperial Formation or Road River Group.

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for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

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