One of the foremost experts on Oklahoma seismicity spoke at a webinar this week for Resources for the Future, highlighting the fact that the steps producers and regulators are taking to address induced seismicity in certain areas of the Arbuckle formation are working. As Stanford geophysicist Mark Zoback said,
“Things are subsiding. The earthquake rate is already heavily down even after six months of reduced injection rates.”
The U.S. Geological Survey announced in late August of this year that the state has seen a 22 percent decrease in magnitude 3.0 or greater earthquakes since the same time period in 2015. A recent EID review of Oklahoma Geological Survey data found 2.8M and greater earthquakes in Oklahoma were down 52 percent between January and April of this year and 55 percent since a June 2015 peak.
These reductions come after the Oklahoma Corporation Commission (OCC) last year implemented a new set of requirements in certain “Areas of Interest,” focusing on injections below the Arbuckle formation. The directive required operators to prove they were not injecting below that zone, or reduce disposal volumes by 50 percent. The state recently expanded that directive, and committed an additional $200,000 to help regulators respond to concerns about earthquakes. This yielded a shut in of 90 wastewater disposal wells and reduced disposal volumes on an additional 250 wells. As a result, the Oklahoma Geological Survey (OGS) has reported about a million fewer barrels per day of wastewater is being injected into Arbuckle wells as of this past spring.
Of course, it’s important to point out that reducing volumes is not inexpensive, and the extra costs have had a whole host of economic impacts on small businesses, local job opportunities, and tax revenue in Oklahoma.
Zoback emphasized that induced seismicity in the state may not cease overnight but the steps producers are taking will continue to yield results,
“It’s going to take a few years for the system to come back to the background rate of natural earthquakes, so it’s not going to be overnight. But it’s certainly the right thing to do and will have a beneficial effect over time.”
And, as he has and many other experts have done before, Zoback explained that “it’s the disposal of very large amounts of produced salt water that is driving the Oklahoma seismicity” rather than the hydraulic fracturing process or the disposal of fracking fluid — both of which many media outlets have incorrectly blamed.
“Basically, it is not hydraulic fracturing and it’s not hydraulic fracturing flowback water. It’s produced water,” Zoback said.
Zoback also noted that just a handful of instances where earthquakes were linked to injection of fracking flowback water — all outside of Oklahoma — and earthquakes linked to the fracking process are extremely rare and even more rarely felt.
“These are magnitude minus one to minus three, which means slip is occurring on a fault that is about a meter in size and about a tenth of a millimeter of slip occurs. And the energy released is on the order of a gallon of milk falling off a kitchen counter and hitting the floor, so you don’t even know what’s happening unless you put seismometers at depth and it’s not consequential.”
Zoback also noted that wastewater injection has not rendered any permanent geological damage in Oklahoma, dispelling another myth perpetuated by fossil fuel opponents who have suggested an all-out ban on produced water injection.
“We’re releasing earthquakes that would have occurred naturally. We’re not really damaging the (geological) system.”