Well of the Week – Without context it is just a squiggle

The Petro Ninja – Enlighten Geoscience Well of the Week is 100/11-22-049-12W5/00 discovery well for the West Pembina Nisku pinnacle reef play. Figure 1 is a production plot to show that it did okay.

Figure 1. Cumulative production history plot for 102/11-22-049-12W5/00.

And that is all I have to say about the history of the Nisku pinnacle play.

Psych! As if that was all I was going to write about. There are several important historical considerations beyond the story behind the odd name of Nairb Petroleums Limited, the proxy company used by Chevron to drill the wildcat.

In the previous Well of the Week, I reviewed an example of the tipping point in the decision to drill an exploratory well and the manifold benefits that can flow from that commitment. But in this modern world, why do such important decisions often hinge on such nebulous inputs as a bend in a river? After all, we have sophisticated facies models, 3D seismic, numerous other tools and awesome computing power.

When pinnacle reefs are mentioned the obvious visual is this photo from last year of a fine specimen off the Great Barrier reef (Figure 2). It certainly isn’t something you could miss if out for a snorkel.

Figure 2. Pinnacle off the Great Barrier Reef, Australia. Nield (2020).

Recent pinnacles are not the same as Devonian pinnacles While the Zeta Lake member of the Nisku, admittedly, only rose 7/10 as high off the sea floor as the Great Barrier Reef pinnacle, perspective is important. Figure 3 is a true scale cross-section of a Zeta Lake pinnacle. The reality is much less dramatic.

Figure 3. True scale cross section of a Zeta Lake pinnacle reef. Exploration Staff, Chevron Standard Limited (1979).

And the data Chevron had to work with was just as subtle. The play developed as Chevron interpreted a 400 km long east to west seismic line from the AB/SK boundary to the region west of Pembina. This seismic was shot to take advantage of the Alberta Geophysical Incentive Credit Program. This program was instituted in the 1970’s to encourage exploration during an industry downturn.

Figure 4. Segment of regional seismic line. Exploration Staff, Chevron Standard Limited (1979).

The segment of this line in Figure 4 shows just how subtle these pinnacles were. Faith in the veracity in what they were seeing required additional seismic and more advanced processing than a Pringles® Potato Chip.

Whether the reader is a non-geologist or an old prospecting hand, it is always important to keep in mind the humbling fact that notwithstanding our extensive knowledge about the Earth we are still making educated guesses about complex systems several hundreds of metres below the surface. As a result, once all possible technical information has been interpreted, we still need to apply our intuition. For example, with all this data and all their considerable knowledge about the basin, the people at Chevron weren’t really certain which formation they were looking at: “Before any of the anomalies were drilled, the possibility that Leduc Reefs were present was considered”, Exploration Staff (1979). The lesson is that once you have interpreted all of the available data, you need to drill a well to find out what is there. And that leads to more questions.

A fourth consideration is the benefit of research in the development of new processing technology and well-considered government support of basinal exploration. The benefits are hard to define at the outset, but the final result usually speaks for themselves.

And finally, I would like to highlight the last sentence on the landmark paper on the exploration process for the West Pembina play: “these factors have led to an important addition to the oil and gas reserves of Alberta and Canada in an area previously considered to be in a mature phase of exploration” (emphasis is mine). But wasn’t the WCSB in a mature phase after Turner Valley and before Leduc? Or was that between Leduc and Pembina? Perhaps it was between West Pembina and the Deep Basin? Maybe the WCSB was whistling past the graveyard prior to the Montney/Duvernay/Oil Sands/Clearwater etc. phase I don’t dispute that the WCSB was considered played out in the mid-1970’s. But it has always risen from the ashes. It is easy to lose track as to how many times the WCSB (and its oil and gas industry) has been considered down for the count. Something to consider the next time you hear someone claiming the end is nigh.

(I would like to thank Clint Tippett for an interesting conversation that sparked both (what I hope is) an interesting angle for this post and a subject for the next one.).

References

Exploration Staff, Chevron Standard Limited; The Geology, Geophysics and Significance of The Nisku Reef Discoveries, West Pembina Area, Alberta, Canada. Bulletin of Canadian Petroleum Geology 1979; 27 (3): 326–359. doi: https://doi.org/10.35767/gscpgbull.27.3.326

Nield, D. 2020. Colossal Reef Discovered Off Australia's Coast Is Taller Than Empire State Building. https://www.sciencealert.com/a-new-reef-discovered-off-australia-s-coast-is-taller-than-the-empire-state-building [accessed: 2023-06-16].