Well of the Week – What is in a name (or a core)?
For a long time, my inner etymologist was intrigued by some names in the Alberta Table of Formations. A case in point is the Grosmont formation. The Grosmont is named after the nearby town of Grosmont. But what is Grosmont named after? Does the northeastern Alberta town have a namesake in Yorkshire? Or is it a reference in French to a Big Mountain? I’m pretty sure no one had the foresight to realize it could refer to a huge mound of oil in the Grosmont carbonates.
This chapter in the Petro Ninja – Enlighten Geoscience Well of the Week series on the New Golden Age of Carbonates features a play that might not quite be ready for prime time but is worthy of inclusion all the same. And with wells as promising as 108/10-26-085-19W4/00, drilled as part of a SAGD pilot, this reservoir is deserving of more attention.
The Grosmont is distinct from the equivalent Leduc reefs in that the distribution of Grosmont platform carbonates was controlled by the extent of basin-filling shales as opposed to subtle topographic changes on the Cooking Lake platform as was the case with the Leduc (Switzer et al., 1994).
Figure 1. Paleogeography of the Frasnian Woodbend Group (from Russel – Houston and Gray, 2014)
Figure 2. Regional structural cross section of the Woodbend Group (from Russel – Houston and Gray, 2014)
As is always the case, the foregoing simplified images do not even begin to tell the story. The Grosmont provides an excellent example of the significant impact diagenetic processes can have on carbonates. The Grosmont features not just a regional paleo-karst feature but localized events that caused paleo-caves (The source material by Russel – Houston and Gray is well-worth a read for a fulsome example of how well, core and seismic data can be interpreted). As we return to these beautiful lithologies for CCUS, lithium and hydrocarbon exploration purposes, it is important to recognize that the fairly simple images on a log suite can actually be representative of a very complex setting.
Figure 3 Grosmont type log. (from Russel – Houston and Gray, 2014)
Figure 4. Photos displaying paleo-cave karst texture. (from Russel – Houston and Gray, 2014)
Success depends on cutting and interpreting lots and lots of core.
Regardless of the current lack of activity in the Grosmont itself, it is important to keep in mind that the current oil sands developments had a false start or two. With an estimated resource of over 406 billion barrels of bitumen in place, the Grosmont formation might very well act as the coda to the symphony of modern carbonates.
I would like to thank Jen Russel – Houston for lending her expertise on the Saleski project. Any errors or omissions are my sole responsibility.
References
Russel-Houston, J. & Gray, K. (2014). Paleokarst in the Grosmont Formation and reservoir implications, Saleski, Alberta, Canada. Interpretation. 2. SF29-SF50. 10.1190/INT-2013-0187.1.
Switzer, S. B., Holland, W. G., Christie, D. S., Graf, G. C., Hedinger, A. S., McAuley, R. J., Wierzbicki, R. A. and Packard, J. J. (1994): Devonian Woodbend-Winterburn Strata of the Western Canada Sedimentary Basin; in Geological Atlas of the Western Canada Sedimentary Basin, G.D. Mossop and I. Shetsen (comp.), Canadian Society of Petroleum Geologists and Alberta Research Council, URL https://ags.aer.ca/publications/chapter-12-devonian-woodbend-winterburn-strata.html, [04/26/2020].