Introduction to October/December Focus: Geophysics in British Columbia and the North

Special Coordinators: Steve Jensen, Draga Talinga, and Stephanie Ross
Format Editor: Elizabeth Atkinson

Geophysics in British Columbia

Aftershock Decay Rate of Large Injection-Induced Earthquakes in Northeast British Columbia: A Case Study for Two sequences in the Montney Play
Amir Mansour Farahbod and Honn Kao

Seismic Attenuation in Northeast British Columbia Using the Coda Q Method
Amir Mansour Farahbod, John F. Cassidy and Honn Kao

In recent years, hydrocarbon exploration and production in northeast British Columbia have increasingly made use of hydrofracking. This is especially true of the Montney play and of the Horn River Basin shale gas play. With the hydrofracking has come an increase in earthquakes. The public and the various governments have taken notice of this development, and one result has been an increased effort to monitor and study the quakes. Government has constructed additional monitoring stations in the area, and a number of operators have installed their own stations. Two papers in this issue make use of this new data to study aspects of NEBC seismicity.

Farahbod and Kao studied the aftershock decay of two of the largest injection-induced earthquakes ever recorded in NE BC. Using the modified Omori law, they found greatly different rates of decay for the two cases. They conclude that the difference relates to geological setting and to the relative strength of pre-existing fracture systems.

Farabod, Cassidy, and Kao study coda-wave attenuation using the single-backscattering model. Using 402 events recorded between August 2013 and January 2017, they calculated attenuation at five frequencies between 2 and 16 hz. and obtained best-estimate fits for Q0, the attenuation at 1 hz. They find that stations in NE BC, despite their stable location on the North American craton, exhibit low Q₀ values.

Geophysics in the North

Mapping the Distribution of Permafrost using the Resolve Airborne EM System: Klondike Highway, Yukon, Canada
Melvin Best, Isaac Fage, and Shawn Ryan

Geophysics in the north is often called upon to address tasks unfamiliar to geophysicists who work farther south. One of these is, of course, diamond exploration. Another is mapping permafrost. Permafrost has long been an object of research for seismologists, who need to deal with its effects on static corrections in the course of hydrocarbon exploration. But permafrost, its presence, absence, and thickness, can be of critical importance to northern civil engineering projects. Warming climate in the north and the accompanying melting of permafrost have only increased the importance of accurate permafrost mapping.

Best, Fage, and Ryan employed airborne electromagnetic surveys (AEM) and drillhole calibration to map permafrost and melted zones under the Klondike highway in the Yukon, with a view to defining zones prone to potholes and fractures. The authors used the RESOLVE AEM sytem to produce a suite of differential resistivity sections along the highway. These sections successfully delineated frozen, partially frozen, and unfrozen ground beneath the highway.

… and more Geophysics on the Prairies

How Geophysics is Used to Understand Geohazards in Potash Mines
Craig Funk, James Isbister, Todd LeBlanc, and Randy Brehm

We have an additional paper for the September focus topic, which was geophysics in the prairie provinces.

Funk, Isbister, LeBlanc, and Brehm describe the use of geophysics to map geohazards in potash mines. The hazards of interest are salt collapses and thin-backs, the latter refering to thinning and weakening of the lower Dawson Bay carbonate, which separates the potash-bearing Prairie Evaporate from overlying aquifers. The authors demonstrate that surface reflection seismic successfully delineates collapse features, but does not unambiguously define thin-backs. They further describe how in-mine refraction and time-domain EM surveys, plus full-space EM modeling, are able to detect thin-back hazards with confidence.

… and yet further afield

Squeezing more from seismic data: Application of prestack simultaneous impedance inversion to a stratigraphic and structurally complex productive field in Argentina
Eduardo Trinchero and Luis Vernengo

There is of course, lots of facinating geophysics beyond our country’s borders. In an article outside of this year’s focus theme, Trinchero and Vernengo take us to Argentina, where they apply modern geophysics to an old conventional oil field, with very positive results.

They describe a reprocessing exercise over a mature field, that included prestack simultaneous impedance inversion to obtain P- and S-impedance attributes, and Vp/Vs ratio. Rock physics parameters derived from seismic compared favourably to the same parameters calculated from well log data. Geologic facies were outlined on cross plots with probability density functions to account for uncertainty, and then seismicly derived rock physics parameters were used to extrapolate the distribution of geologic facies. Pay is predicted by low impedance and low Vp/Vs ratio, and new drilling through such targets has been successful.

CSEG RECORDER – come join our team!

The final part of the year has been difficult for the CSEG RECORDER team. With the challenges in our industry, it is harder to find content, and the team struggled to fill content for separate British Columbia and Northern issues. Thanks so much to all of our authors who have contributed excellent work.

The RECORDER team, and indeed all of CSEG’s volunteers, are under more stress – those who are working are often overloaded, and those who aren’t employed are working even harder and facing the emotional challenges that come with that. Our chief editor Brian Schulte started a new job that, quite understandably, suddenly took the majority of his time. Brian was carrying so much of the load that when he had to pull back, it was keenly felt. Thanks so much, Brian, for everything you’ve done!

The RECORDER remains a great communication tool, and it is very interesting and genuinely fun to work on the team. We are developing better processes to cover for each other and more smoothly produce content for the digital age. We need CSEG members to suggest topics and possible articles/authors. We need the other CSEG committees to send us their news and advertisements. And we need more team members –“Many hands make light work”. We need new leaders, more technical editors, and more format editors. If you’d like to join us, please contact the CSEG office and the chief editor at editor@CSEGRecorder.com.