Hydraulic fracturing, or fracking – a method of extracting oil or natural gas from shale deposits – has injected much-needed cash into struggling communities in Ohio, Pennsylvania, West Virginia, and other states. But along with those economic benefits come some health and safety concerns, among them the question of whether fracking might cause earthquakes.
Mike Brudzinski, a professor in Miami University’s Department of Geology & Environmental Earth Science, first became interested in this question in 2012, following a series of earthquakes near Youngstown, Ohio. The area had not previously seen seismic activity, and Brudzinski was intrigued by speculation that the earthquakes were caused by a wastewater injection well.
In hydraulic fracturing, a pressurized mixture of water, sand, and chemicals is pumped into a well to crack underground shale, thereby releasing oil or natural gas trapped in the rock. This process generates wastewater, and while some of it can be recycled, large volumes need to be stored deep in the Earth, far away from our drinking water. The inception of the Youngstown earthquakes seemed to coincide with the inception of a nearby wastewater injection well operation.
Acting on a hunch that he could adapt a technique that had been used to identify repeating earthquakes in subduction zones, Brudzinski worked with former doctoral student Steve Holtkamp, masters student Rob Skoumal, and departmental colleague Brian Currie to develop a technique for taking an earthquake’s “fingerprint” from a network of monitoring stations and then scanning for matches by looking for similar signals.
The technique (see more here) works, Brudzinski says, because injection wells “cause some stress at a very localized point, so it appears that any resulting slip on the fault is very localized as well. It’s probably not the exact same patch of the fault that’s moving, but it’s so close that the earthquakes look the same to the stations farther away.”
Eventually, the team was able to use the Youngstown earthquake’s fingerprint to identify about 550 previously undetected, smaller earthquakes hidden in data collected by regional seismometers 100 miles or more away. Specifically, they found that:
- The earthquakes began almost immediately after injection began at the well in question;
- The earthquakes moved away from the well over time;
- There was a strong correlation between the total number of earthquakes and the amount of wastewater injected into the well.
Since then, Brudzinski has analyzed more data and has found a total of six cases of induced earthquakes in Ohio. He says about half of these cases result directly from the hydraulic fracturing process, while the other half result from wastewater injection.
“And there are a lot more fracking wells in Ohio than wastewater injection wells,” he says, “so fracking itself seems less likely to produce earthquakes than wastewater injection.”
Brudzinski and his colleagues’ most recent study, which generated a swirl of media attention when it was published at the beginning of 2015, helped explain why earthquakes during the fracturing process appear to be so rare. In their study southeast of Youngstown, they found that fracking generated earthquakes only when the well was operating less than a half mile from a pre-existing fault.
Even when you consider the wastewater injection cases, earthquakes are not exactly common here. Brudzinski estimates that only 1-2% of the injection wells in Ohio have caused seismic events. Given the relatively low risk, Brudzinski thinks that his work should not be used to justify bans on fracking in Ohio, similar to the one announced in New York this past December.
“There is a lot of economic stimulation for Ohio going on right now because of fracking and wastewater injection,” Brudzinski says. “This is now an opportunity for economically depressed parts of the state to rebound, and the Ohio Department of Natural Resources is enacting regulations that will reduce the likelihood of future felt induced earthquakes in the state. ”
Brudzinski says that under current regulations, any seismic event that measures greater than a magnitude 1.0 prompts a pause in operations, while any seismic event with a magnitude of 2.0 or greater prompts a complete halt.
“If an earthquake is below a magnitude 3.0, it is unlikely to be felt, and so there’s really no direct influence on the general public,” Brudzinski says. “But there’s a concern from seismologists that just a bunch of little earthquakes isn’t necessarily okay, because we typically see the rates of large earthquakes increase as well. And if the rate of small earthquakes in an area jumps from one per 100 years to ten per year, it suggests larger earthquakes could be much more likely if the operation responsible for the events is not altered.”
Many in the oil and gas industry say Ohio’s current regulations are conservative, and Brudzinski agrees that they are. But while some in the industry might say that regulators are being too aggressive, Brudzinski sees them as merely cautious.
“I think the target is that we’d only see a couple of magnitude 2.0 events, and maybe a dozen or so magnitude 1.0 events. That means it should be unlikely that we’d get another 4.0, let alone a 5.0 or 6.0, which would be much more likely to cause damage.”
To make sure the right balance is being struck between the economic benefits brought by the oil and gas industry and the possibility of inducing earthquakes, Brudzinski says it’s important for regulators and operators to work in partnership with scientists like him, who are working on new techniques to analyze and interpret data rapidly.
“Our earthquake fingerprint scanning technique is set up to investigate any new earthquake for evidence that it’s induced with results returned in less than a half hour,” Brudzinski says. “And our current studies are going back through the catalog of older earthquakes to look for new insights about the physics of how earthquakes are induced.”
In addition, Brudzinski says he’s working on obtaining federal support for research that would help Ohio and other states make better-informed policy decisions. He says that’s difficult right now because the federal agencies are still figuring out who can afford this new fracking research. Ultimately, Brudzinski feels the National Science Foundation (NSF) will eventually take on a primary role because much of the work that needs to be done falls in the category of basic research, and he recognizes that researchers have a responsibility to help demonstrate that.
“It’s on us as investigators to write proposals that make that part clear – while this has impact on society because of the potential to influence hazards in certain areas,” he says, “we still need to understand the basic physics of what’s going on to better assess how much the hazards are changing.”
Doing that will help ensure that Ohio and other states can safely reap the economic rewards of this method of energy extraction.
Written by Heather Beattey Johnston, Associate Director and Information Coordinator, Office for the Advancement of Research & Scholarship, Miami University.