Last week we discussed the importance of recognizing regional unconformities, correlating offshore sequences to predict where these will culminate in reservoir facies, and the interplay between the two. This week the Petro Ninja – Enlighten Geoscience Well of the Week will focus on a singular sedimentary feature of the Doig formation that was the subject of much study from 1989 through 2011.
Agreement was reached early on in the debate to refer to these features with the (somewhat ponderous) term anomalously thick sandstone bodies (Wittenberg and Moslow, 1991) or ATSB (perhaps one too many initials in that acronym for some). In the final analysis, it serves as another example of the importance of considering penecontemporaneous structuring in stratigraphic interpretation.
After all of the academic dust settled, a meta-analysis by Dixon (2011) provides a good overview of the ATSB phenomena.
Dip cross-sections through ATSBs in Progress, AB and Dawson Creek, BC (Dixon, 2011).
Schematic map of ATSBs (Dixon, 2011).
Dixon summarized the provenance of ATSBS as most likely
“The most probable explanation for the origin of ATSBs is that during late regression, structural depressions formed on a muddy, pre-existing shelf and were filled by sandy sediment. Initial deposits in the thicker sandstone bodies commonly are debris-flow and/or slump deposits that filled in the deeper parts of the depression. As the depression filled, sediment entered wave- and current-influenced water depths and more typical shoreface deposits began to form. As regression proceeded some sandstone bodies were truncated by a regressive surface of marine erosion. Finally, all ATSBs and adjacent sediment were capped by a thin veneer of transgressive sediment.” A plain language version might read: These features are the result of faulting, and they were subsequently modified by more orthodox sedimentological processes.
- Attempts to capitalize on the resource in place met with limited success due to the reservoir compartmentalization resulting from faulting and complex internal stratigraphy. More recent drilling has been more fruitful as illustrated by the Buick Creek field in NEBC and, in particular, well 200/B-097-I/094-A-12/00
Isopach map of Buick Creek ATSB (Dixon, 2011).
Production forecast for 200/B-097-I/094-A-12/00. Courtesy of Subsurface Dynamics.
References
Dixon, J., 2011. A review of the character and interpreted origins of thick, mudstone-encased sandstone bodies in the Middle Triassic Doig Formation of Western Canada. Bulletin of Canadian Petroleum Geology. 59 (3): 261–276. doi: https://doi.org/10.2113/gscpgbull.59.3.261
Wittenberg, J. and Moslow, T. F., 1991. Origin and facies variability of overthickened sandstones in the Doig Formation, west-central Alberta. Bulletin of Canadian Petroleum Geology. 39 (2): 228. doi: https://doi.org/10.35767/gscpgbull.39.2.228c