‘I think it’s really just a matter of time before we start seeing damage coming out of this …’
Researchers in western Canada tracking the link between fracking and earthquakes have come to a different conclusion than scientists studying the same issue in the U.S.
Instead of pointing to wastewater injection as the cause of induced earthquakes, the Canadian scientists suggest there may be a direct link between fracking and induced earthquakes.
Research in the central U.S. has suggested that the sharp increase in quakes in places like Oklahoma are caused primarily by massive amounts of wastewater injected back into the ground after oil and gas recovery.
The new Canadian study doesn’t explain why induced seismicity would be linked to different processes in the central U.S. and western Canada. However, some oil and gas fields in the U.S., especially Oklahoma, use “very large amounts of water” in their operations, leading to much more wastewater disposal than in Canadian operations, said Gail M. Atkinson of Western University.
As a result, the seismicity induced by wastewater injection may be masking another signal of earthquakes caused directly by fracking, “So we’re not entirely sure that there isn’t more seismicity in the central U.S. from hydraulic fracturing than is widely recognized.”
The fracking process uses high-pressure injections of fluid to break apart rock and release trapped oil and natural gas. Both fracking and wastewater injections can increase the fluid pressure in the natural pores and fractures in rock, or change the state of stress on existing faults, to produce earthquakes.
Similar to huge fracking zones in the U.S., parts of western Canada are laced with thousands of fracking wells drilled in multi-stage horizontal operations. Atkinson and her colleagues compared the relationship of 12,289 fracking wells and 1236 wastewater disposal wells to magnitude 3 or larger earthquakes in an area of 454,000 square kilometers near the border between Alberta and British Columbia, between 1985 and 2015.
The findings, published online in the journal Seismological Research Letters, were explained in a press release.
The researchers performed statistical analyses to determine which earthquakes were most likely to be related to hydraulic fracturing, given their location and timing. The analyses identified earthquakes as being related to fracking if they took place close to a well and within a time window spanning the start of fracking to three months after its completion, and if other causes, such as wastewater disposal, were not involved.
Atkinson and colleagues found 39 hydraulic fracturing wells (0.3 percent of the total of fracking wells studied), and 17 wastewater disposal wells (1 percent of the disposal wells studied) that could be linked to earthquakes of magnitude 3 or larger.
While these percentages sound small, Atkinson pointed out that thousands of hydraulic fracturing wells are being drilled every year in western Canada, increasing the likelihood of earthquake activity.
“We haven’t had a large earthquake near vulnerable infrastructure yet,” she said, “but I think it’s really just a matter of time before we start seeing damage coming out of this,” Atkinson said.
The study also confirmed that in the last few years nearly all the region’s overall seismicity of magnitude 3 or larger has been induced by human activity. More than 60 percent of these quakes are linked to hydraulic fracture, about 30-35 percent come from disposal wells, and only 5 to 10 percent of the earthquakes have a natural tectonic origin, Atkinson said.
Atkinson said the new numbers could be used to recalculate the seismic hazard for the region, which could impact everything from building codes to safety assessments of critical infrastructure such as dams and bridges.
“Everything has been designed and assessed in terms of earthquake hazard in the past, considering the natural hazard,” she said. “And now we’ve fundamentally changed that, and so our seismic hazard picture has changed.”
The researchers were also surprised to find that their data showed no relationship between the volume of fluid injected at a hydraulic fracturing well site and the maximum magnitude of its induced earthquake.
“It had previously been believed that hydraulic fracturing couldn’t trigger larger earthquakes because the fluid volumes were so small compared to that of a disposal well,” Atkinson explained. “But if there isn’t any relationship between the maximum magnitude and the fluid disposal, then potentially one could trigger larger events if the fluid pressures find their way to a suitably stressed fault.”
Atkinson and her colleagues hope to refine their analyses to include other variables, such as information about extraction processes and the geology at individual well sites, “to help us understand why some areas seem much more prone to induced seismicity than others.”
The scientists say the seismic risks associated with hydraulic fracturing could increase as oil and gas companies expand fracking’s use in developing countries, which often contain dense populations and earthquake-vulnerable infrastructure.