Shale in a Northern Canadian Basin: Unconventional Gas Potential of Middle and Upper Devonian Strata, Eagle Plain Region, Yukon Territory, Canada
Eagle Plain is a frontier oil and gas basin in northern Yukon, Canada. The basin covers >20 000km2, and is underlain by up to 5800m of Paleozoic and Mesozoic strata. Estimates of the conventional petroleum potential for the basin are 437 MMbbls oil and 6 Tcf gas. The unconventional potential of the basin has not been assessed.
This study characterizes potential shale gas strata in Eagle Plain basin. Fresh diamond drill core and outcrop samples were collected from Devonian strata of the Road River Group and Canol and Imperial formations in the Richardson Mountains, along the eastern fringe of the basin. Rock-Eval pyrolysis (RE), vitrinite reflectance (VR) and organic petrology were performed on shale samples to asses organic matter quantity, type and thermal maturity. X-ray diffraction (XRD) was conducted to assess quartz, clay and carbonate mineralogy.
VR results show that all samples are overmature with respect to oil generation (1.89%RoR to 3.86 %RoR). However, values systematically decrease southward along the mountain front through the dry gas window to the upper limit of the mixed wet/dry gas window (2.00 %RoR). The high thermal maturity of samples render RE-derived parameters unreliable hence type and thermal maturity of organic matter could not be determined via this technique. Organic petrology identified organic macerals that could be classified as Type I and II kerogen in Road River Group and Canol strata while Imperial strata are organically lean.
Total organic carbon (TOC) values for the Canol Formation are high, ranging from 0.3-20 wt% with most 2-5 wt%. For the Road River, TOC values are between 1-19 wt % with most <5 wt%. The Imperial Formation registered the lowest TOC values mainly <1 wt%.
XRD analyses indicate the succession is highly siliceous, particularly the Canol Formation with quartz values 91-100%. Samples of the Imperial Formation are generally 82-96% quartz, while Road River samples are more variable with a spread of 62-98% quartz.
This study suggests these strata may have shale gas potential in the region assuming favourable burial conditions are met. Canol Formation and Road River Group shale are most promising based on the high TOC values and identifiable organic maceral types, suggesting they may have been richer source rocks in the past. All strata are highly siliceous, with the Canol Formation more consistently quartz-rich than the Road River and Imperial formations. A 2010 study of subsurface Canol and Imperial formation shale west of the study area indicates these formations are within the oil window within Eagle Plain basin. These results highlight the potential for shale gas and liquids in the region.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California