Introduction to November Focus: Induced Seismicity

As professional geophysicists and engineers it is mandatory to put public safety above any other aspects of our professional practice. The widespread usage of hydraulic fracturing (HF) of unconventional resources (shale gas) has created multiple questions in the public mind about the short and long term effects on residents near the production areas. One of these questions is whether artificial fracturing of a reservoir rock, mining activities or reservoir impoundments can trigger earthquakes by releasing the tension stored in the regional geological faults. This is commonly known as “induced seismicity” in the geophysics community. In this issue of the RECORDER we have gathered articles related to induced seismicity. These articles cover a wide range of the physics and geomechanics of induced seismicity to studies on the monitoring of induced seismic events.

The first article by Doug Schmitt starts a great summary on the history of induced seismicity in Canada and around the world. A good bulk of this article provides a tutorial on understanding the physics and geomechanics of in situ processes leading to induced seismicity. This article also explores possible contributions that geophysicists can make to future research projects in this area.

The second article by Dave Eaton describes Alberta Telemetered Seismograph Network (ATSN) and the light that it can shed on induced seismicity in western Canada. The ATSN has been operational since 2009 and its data has been used for regional seismicity and deep lithosphere studies.

The third article (Scott Cairns et al.) describes the effort undertaken to monitor induced seismicity in the Northwest Territories by the Geological Survey of Canada. The network was installed to address the concerns of residents about the connection between hydraulic fracturing and small magnitude earthquakes. This network has been recording seismic events since its installation ahead of any fracturing activity in the region. This will provide a baseline for the natural seismicity of the region and a good calibration to identify any induced seismicity by production activities in the future.

The fourth article (Amir Mansour Farahbod et al.) is a collaborative study between the Geological Survey of Canada and British Colombia Oil and Gas Commission (BCOGC) on regional seismicity in Northeast British Colombia (NEBC). Their initial analyses of collected data indicate that “the apparent aseismic nature of this region was largely an artifact of a lack of seismic monitoring stations.” The NEBC seismic monitoring network can now detect a larger number of smaller magnitude events. Initial studies also suggest a correlation between HF and the seismicity of the region.

For the fifth article of this special issue (Ahmed Ouenes et al.), we shift gears back to the exploration aspects of the spontaneous seismic events caused by HF. The article introduces a new geomechanical workflow for modeling the interaction between hydraulic and natural fractures. The authors used the proposed geomechanical workflow to predict the differential stress, frac stage performance and microseismicity.