Injector(s) of the Week – Induced Seismicity had to start somewhere

I feel the earth

Move

Under my feet

I feel the sky tumbling down

I feel my heart start to trembling

When you shake the ground

(With apologies to Carole King, composer of the actual song.)

Evidence of the importance of understanding and mitigating seismicity induced by industrial applications was provided by last week’s GeoConvention. By my count, there was one session with 7 talks dedicated to induced seismicity and 5 other sessions with another 7 talks discussing this theme. There were also 3 posters on the subject. And it wouldn’t be surprising if the topic popped up in other presentations as well. Evidence that regulators understand the seriousness of this issue is seen in the recently revised Directive 65 from the Alberta Energy Regulator. The best way to delve into a story is to start at the beginning. So, this week’s Stack DX (Petro Ninja has a new name!) – Enlighten Geoscience Well(s) of the Week will discuss what is understood to be the first injection induced seismicity in western Canada.

The Spring of 1970 saw landmark seismic events, both literal and figurative. The literal one was the first induced seismic event in western Canada on March 8, 1970. This earthquake was nucleated in an otherwise aseismic area of north-central Alberta and attributed to waste water injection in the Snipe Lake Beaverhill Lake oil field (Milne, 1985). With a ML of 5.1 it was felt by the nearby residents and was, undoubtedly, a memorable event.

The Earthquakes Canada database doesn’t store events occurring prior to 1985, and monitoring networks were much less well-established than today, so there is some uncertainty in the location, depth and magnitude of the event and, therefore, the ability to attribute the event to a particular well. Rigorous and modern analysis often provides very compelling evidence that seismogenic faults often reside much shallower than area induced seismic events.

But if, for the sake of argument, we go with the conclusion this first earthquake was caused by waste water disposal into the Snipe Lake Beaverhill Lake oil pool, it is possible to narrow the possible culprits down to 100/02-11-070-18W5/00 (2-11) and 100/10-28-070-18W5/00 (10-28), since these were the only injectors operational at the time. These wells are illustrated in Figure 1.

Figure 1: Map of Snipe Lake Beaverhill Lake oil pool with probable seismogenic wells highlighted in blue.

From 1965 to March 1970, 2-11 injected 15,608.5 m3 of water and 10-28 injected 22,858.3 m3 for a total injection volume of 38,466.8 m3. A significant volume, but total injection of 37,915,120 m3 over the entire life of the field is almost 10 times that amount without any further seismicity. A plot of Calendar Monthly Water Injection for both wells and the total injection from the start of injection until March 8, 1970 is shown as Figure 2.

Figure 2: Calendar Monthly Water Injection plot for Snipe Lake Beaverhill Lake oil pool.

Nothing really stands out except, perhaps, a ramping up (not for the first time) of the injection rate in the six months prior to the earthquake, particularly from 10-28. Is this enough evidence to designate 10-28 as the seismogenic well? Definitely not, since great care should be taken before assigning that stigma.

That is the story, such as it is, of the literal seismic event from early 1970. The figurative seismic events? Well, within a month of the Snipe Lake induced seismicity, a British band you may have heard of officially broke up. And the next year, Carole King released Tapestry which included the earthquake adjacent references in the introductory quotation. Far be it for me to suggest these popular culture milestones were inspired by ground motion in far away Alberta, but I haven’t found any evidence that they weren’t is all I’m saying.

References

W. G. Milne. 1970. The Snipe Lake, Alberta earthquake of March 8, 1970. Canadian Journal of Earth Sciences. 7(6): 1564-1567. https://doi.org/10.1139/e70-148