By Ganesh Murdeshwar
Vice President, Canada
If you are an operator working in the Kaybob area of the Duvernay in Alberta, you've probably heard of AER Subsurface Order No. 2! If you haven't, it basically means this - any well completed using hydraulic fracturing in this zone must be monitored for seismicity, with a network sufficient to detect a 2.0 magnitude event within five km of any such well.
The order came in response to a 4.4 magnitude event, felt in the town of Fox Creek on January 22nd, and it's the first time the Alberta Energy Regulator (AER) has mandated this type of monitoring.
It caught a lot of operators by surprise.
While the imposition of these new monitoring requirements does add some overhead, it shouldn’t be too complicated or expensive!
As a direct response to the AER order, MSI has started the development and installation of a permanent seismicity monitoring solution we call AlertArray™. This array will cover the entire ~14,000 sq km area affected by the AER order, which is roughly the size of the State of Connecticut!
MSI has designed a sophisticated hybrid network, blending sondes with seismometers to provide the best possible detection, location, and magnitude accuracy. The hybrid approach is unique, since many arrays only use a network of seismometers to implement seismicity monitoring. While solely using seismometers can work, it does come with some significant challenges.
For example, we find that seismometers (the instruments themselves) can be quite delicate. To ensure that they make it to the field safely, we have our technicians carry them in their arms during the trip out to the field!
Additionally, a seismometer can also be easy to setup - too easy. If you're not conscientious about the installation process, you can just plunk one on the ground, cover it with something, and call it a day. Unfortunately, in that situation, the sensitivity of the instrument can be a real problem - temperature fluctuations and ground noise can wreak havoc with detecting that all-important event signal.
Instead, MSI use the mentioned hybrid approach for all of our seismicity monitoring arrays, including AlertArray. The primary instrument used within the hybrid system is our tried and true BuriedArray® sonde. The system is bulletproof. I mean that literally - I think you could shoot one with a bullet and it would still work. These sondes are outstanding at detecting and locating events. At 5 m deep, the system is isolated from temperature variation and surface noise, which correlates to reliable detection and location for even the smallest events.
However, there is a catch. Sondes have frequency characteristics that can result in increased uncertainty in resolving the magnitude of larger events. To address this concern, MSI seismicity monitoring networks use at least one seismometer, or comparable broadband instrument, to calibrate large magnitude detections. AlertArray, specifically, has two for redundancy.
For maximum performance, the seismometers are installed in a metal vault, about 1m deep, placed on a leveled concrete pad, and placed firmly on undisturbed ground. The seismometer is covered in sand to provide thermal coupling with the ground, and the vault is filled with insulation and locked under a water proof cover.
With the hybrid approach, we can be sure that the sensitivity of the system is protected and that the instruments will be there when we need them.
At MSI we go to great lengths to ensure that we give our clients the best and most reliable detection technology, and our seismicity network is no exception
I hope you enjoyed getting a peek "under the covers" of our detection technology!