Earthquakes linked to oilpatch activity Deep well injections of wastewater seen triggering minor quakes in U.S.
By Dina O'Meara, Calgary Herald April 10, 2012
CALGARY - Provincial regulators and petroleum producers in Western Canada are waiting with keen interest on the results of several studies looking into possible links between industry activity and an increase in minor earthquakes.
While Alberta has increased the number of earthquake monitoring devices across the province to better understand seismic activity over the past decade, British Columbia will be releasing a study this summer on possible links between seismic activity and drilling.
More immediately, a new study conducted by the U.S. Geological Survey points to human interference affecting an “unprecedented” spike in mini-earthquake activity around areas of intense oil and gas production.
The activity is related to injection of wastewater into deep wells and not hydraulic fracturing activities, said co-author William Ellsworth.
“What we found is that there are earthquakes in association with locations where wastewater is being disposed of underground,” Ellsworth said in an interview with CNBC. “This is not news; we’ve known about this for decades that under certain conditions it’s possible to trigger earthquakes by pumping fluids underground.”
The report, to be presented next week in San Diego, notes the average number of minor quakes in the U.S. midcontinent have increased steadily since 2001, culminating in a six-fold jump in seismic activity in 2011.
“A naturally occurring rate change of this magnitude is unprecedented outside of volcanic settings or in the absence of a main shock, of which there were neither in this region,” the report said. “While the seismicity rate changes described here are almost certainly man-made, it remains to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production.”
Knowing if the geology is more prone to producing earthquakes will be useful in determining if a site is appropriate for long-term waste disposal, said Dave Eaton, professor of geophysics and head of the University of Calgary’s Department of Geoscience.
“The model is if you can localize where these small earthquakes are occurring you can get a better understanding of potential areas where larger earthquakes could occur,” he said. “Even if the earthquakes are small and don’t cause any damage, it’s important to get a better understanding of where they are taking place.”
The B.C. study was launched after a series of minor quakes were registered in the northeast corner of the province, an area historically clear of seismic activity, said Dan Walker, geologist with the B.C. Oil and Gas Commission.
Between late 2009 and the end of 2011, approximately 31 quakes were registered in the Etscho area, about 80 kilometres north of Fort Nelson, with another seven quakes registered in the Tattoo area, about 50 kilometres further north.
“They were in areas where there is fracking activity and where there had been no seismicity reported before, that’s really what sparked the inquiry,” Walker said.
The study isn’t unique. In the mid 1990s, the province looked into a cluster of earthquakes that occurred north of Fort St. John a decade before. The study resulted in tighter regulations limiting reservoir pressures after concluding that waterflooding of a well induced the seismic activity.
Scientists in Western Canada are monitoring areas that are typically quiet and trying figuring out what is natural and what could be human induced, said John Cassidy, head of earthquake seismology for Natural Resources Canada.
Alberta typically has had little natural seismic activity — about 470 tremors in the past quarter century, most in the southeast foothills — but did register a surprise level 5.4 quake in the northwest of the province in 2001, he said.
“We do have natural earthquakes which occur in relatively quiet regions as a result of tectonic stress,” Cassidy said. “The challenge is what are the real earthquakes versus induced seismicity.”
Cassidy noted quakes that register under level 3 on the Richter scale — such as the ones recorded in northeast B.C. — are considered minor and often are barely felt.
The oilpatch has known for years there can be seismic activity due to deep wastewater well injections and fracturing, which involves pumping fluids into the ground at high pressure to enable oil and gas to leak out of tight formations.
“We haven’t seen anything in Alberta, but we have had a lot of activity in the province over the last 60-70 years and that involves deep disposal wells,” said Travis Davis, spokesman with the Canadian Association of Petroleum Producers. “It’s important to let some of the science shine a light on the issue on whether it’s related specifically to fracking, or whether it’s the way you dispose of water.”
The use and disposal of water has become an important issue for producers seeking to increase recycle rates and reduce costs, Davis noted.http://www.calgaryherald.com/news/Earth ... z1rjtYVljo