Latest research shows that location of “slip-ready fault” key to cause of induced-seismicity
A hydraulic fracturing operation in northeast BC was shut down on Nov. 29 after triggering earthquakes of 3.4 to 4.5, the BC Oil and Gas Commission announced Friday.
Canadian Natural Resources Ltd. (CNRL) stopped fracking after its seismic monitoring equipment detected the quakes. BCOGC regulations normally require suspending activity at 4.0, but a special order issued in May lowered the threshold to 3.0 for the project operating in the Septimus field of the Montney formation southeast of Fort St. John.
Companies operating within the area confirmed to the Commission there will be no fracking over the next 30 days during the investigation and they require permission to restart operations.
The Commission is the first North American regulator to identify the link between fracking and induced seismicity, publishing studies in 2012 and 2014 that identified hundreds of small micro-earthquakes (between 1.8 and 3.0) caused by the process of pumping water, sand, and chemicals into rock formations to free trapped oil so that it can be pumped to the surface.
Research by University of Alberta and the Alberta Geological Survey published earlier this year showed that the volume of hydraulic fracturing fluid and the location of well pads control the frequency and occurrence of measurable earthquakes. Researchers were stuying large earthquakes over 4.0 in the Fox Creek, Alberta region.
Seismologist Ryan Schultz found that when increased volumes were injected in susceptible locations, with a nearby slip-ready fault, the increased pressure on the fault line led to more numerous measurable earthquakes.
This is a new insight, says Schultz. Scientists have understood the connection between volume and induced seismicity since the 1950s, but the influence of well pad location was not well known.
“If there is a pre-existing fault, but you’re not connected to it by some sort of fluid pathway, you can hydraulically fracture the formation, and you’re probably not going to cause a significant earthquake,” said Schultz.
“It’s conceptually quite simple, but actually determining those things underground is really hard to do in practice.”
Public concern about fracking-induced earthquakes has been on the rise over the past few years after Oklahoma reported a high number of seismic events linked to oil and gas production. Investigators found that most of those events were caused by wastewater injection wells, which pump produced water from operations underground at high pressure over a number of years.
Texas also reported a rise in induced seismicity, especially in the northern of the state encompassed by the Barnett Shale formation, which primarily produces natural gas.
Regulators in almost all oil and gas producing jurisdictions have since introduced hydraulic fracturing regulations and protocols that require enhanced seismic monitoring, stop orders if earthquakes are detected, and investigations before fracking is allowed to resume.