Studying outcrop sections is a cost effective way to obtain datasets comparable to those that may be obtained from long, continuous drill cores. These studies have the added benefit of enabling larger-scale lateral observations. In particular, critical observations can be made about lithology, depositional environments, stacking patterns and sequence stratigraphic interpretations that can be extrapolated to wireline log and seismic data for the subsurface play analysis.
The caveat of extrapolating outcrop data to the subsurface is that uplifted and exhumed outcrops may exhibit the effects of a retrograde pressure and temperature history. Mechanical and chemical surface weathering processes can dramatically alter rock properties. This means we need to be cautious when extrapolating aspects of the plays such as maturity, porosity, and mechanical properties of the outcrops to the subsurface. However, within these constraints, outcrop data can add value in understanding play commodity type, reservoir quality, and mechanical properties as well as general lithology, depositional setting and sequence stratigraphic interpretation.
In this study we integrate outcrop observations made in the Mackenzie Mountains, Northwest Territories, Canada to further our understanding of relatively data-poor Devonian-aged shale plays in the adjacent Peel and Mackenzie Valley Basins. Several vertical sections were measured and correlated to understand the distribution of lithofacies within a sequence stratigraphic framework. This allows us to deduce depositional settings and understand the distribution of favorable shale reservoir types in the area. Spectral Gamma Ray profiles measured in outcrops were used to correlate surfaces from outcrop to well logs in the basins.
We found that the basin architecture and the presence of both siliciclastic and carbonate depositional systems provide first-order controls on the distribution of favorable shale reservoirs. The learnings from the outcrop work can be used to better understand other age-equivalent shale plays in North America that lack high-quality outcrops.