Oil and gas companies can influence the number of fracking-related earthquakes they may unintentionally generate by changing the volume of fluids injected during the extraction process, a study by Western seismic expert Gail Atkinson shows.
The volume of material used during fracking is directly related to the rate of induced earthquakes, according to the study newly published in Science, but the volume doesn’t necessarily control the magnitude of the biggest event.
Hydraulic fracturing, also called fracking, entails drilling a vertical shaft into deep shale until it reaches an oil bed, then drilling a horizontal shaft and injecting fluid into the rock to release pockets of entrapped gas. The process has been linked to an increase in seismic activity in some areas.
Atkinson said Fox Creek, Alta., became the “poster child” for study because of a sharp increase in quake activity there after fracking began - with many felt events, including one with a magnitude of 4.4, in June 2016. The area is part of the Duvernay Formation, a geological feature of north-central Alberta rich in shale, oil and gas.
Atkinson is the NSERC/TransAlta/Nanometrics Industrial Research Chair in Hazards from Induced Seismicity and teamed with researchers at the Alberta Geological Survey, University of Alberta, University of Calgary and Natural Resources Canada on the study.
“This is an important finding because some previously held theories propose there is a relationship between the largest magnitude of the earthquake and the injected volume, but what we have found is the maximum magnitude isn’t what’s being controlled by the volume – it’s the earthquake rate,” Atkinson said.
The two theories are related, though, because the more earthquakes are induced, the greater the potential a larger one might occur.
“The more we can lower the rate of earthquakes, the less likely the chances we generate a larger one,” she said.
She sounded a warning there’s no guarantee controlling volume will limit the maximum magnitude of a quake. “Industry still needs to be very careful where they conduct hydraulic fracturing operations. They have to stay away from critical infrastructure to prevent a damaging event.”
Atkinson and fellow researchers have previously shown there is a correlation between earthquakes at magnitude 3.0 and higher and industrial fracking operations.
She noted fracking doesn’t always cause earthquakes and earthquakes don’t always result from fracking. “There are a lot of places people frack and they never generate an earthquake.”
Injection volume and geological factors together account for about 96 per cent of the earthquakes in the Fox Creek area, Atkinson added.
During fracking, a mixture of water, sand and chemicals is injected into the rock at high pressure, which causes small fissures to form in the rock and release entrapped natural gas.
The study found injection pressure and rate had an insignificant association with seismic response.
The results of this study may influence policy and practice in the oil fields, Atkinson said.
“(Regulators) would certainly use this to guide policy decision and inform industry,” she said. “Industry pays attention to these developments. They obviously don’t want to generate earthquakes; that’s bad for business.”
She said the research also speaks to the importance of assessing cost and benefit and managing risk in industry, or any endeavour. The risk of earthquakes remains low and, while fracking remains controversial and has detractors, it has become an economically feasible way of bringing affordable gas to consumers.
According to Atkinson, there are promising signs industry can change or modify existing practices to reduce the number of induced earthquakes, while still getting the results they want.
“There is some indication industry is getting better at limiting induced earthquakes as the number of induced events has gone down in a number of jurisdictions, like Alberta and Oklahoma, over the past year,” Atkinson said. “For a while, every year, the largest event that was induced was the largest to date and we haven’t seen anything bigger this year than we have before. That may be a sign industry is figuring some of these things out.”