Oklahoma’s surge in seismic activity has cultivated a swath of land with earthquake sequences “unheard of” in any other comparably sized area of the globe and may also produce a 6.0 temblor, according to a U.S. Geological Survey geophysicist.
But some efforts to mitigate quakes that rattled Cushing a year ago — through more stringent wastewater disposal regulations — have yielded positive empirical results, and it’s a clear indicator that the issue of induced seismicity is manageable. That’s according to Daniel McNamara, a USGS research geophysicist at the National Earthquake Information Center.
Oklahomans remain shaken up as the state blasts through its earthquake record from only a year ago. In August Oklahoma surpassed 2014’s banner year of 584 earthquakes of 3.0 magnitude or greater. In 2015, Oklahoma Geological Survey data show a staggering 802 quakes of those magnitudes through Sunday afternoon.
Although he says more data are needed, McNamara harbors hope for solutions between the oil and gas industry and policymakers. Until then, the state’s incessant shaking serves as a reminder to McNamara’s concern that a damaging quake could strike near heavily populated Oklahoma City or Cushing, a central hub of the nation’s oil pipeline network.
Several fault zones appear capable of 5- or 6- magnitude quakes
The magnitude-4.7 quake near Cherokee early Thursday was the state’s largest since one of Prague’s aftershocks in 2011. The main event and the state’s largest recorded earthquake was a 5.6-magnitude temblor that struck Nov. 6, 2011. It caused at least two injuries, destroyed 14 homes and damaged many more.
McNamara warns that the hazard is quite real for another Prague-sized quake near a population center or critical infrastructure. When evaluating that sequence, McNamara notes that there were two magnitude 4s the year before and one the day before.
Through Sunday afternoon, Oklahoma has been rocked by 31 magnitude-4 or greater earthquakes in 2015, according to Oklahoma Geological Survey data.
McNamara described the number of magnitude 4s in 2015 as “unheard of in any other similar-sized region on the planet that we know of.” He explained that scientists see similar sequences or numbers associated with large earthquakes such as those in Nepal and Japan.
What is “very strange” about Oklahoma is the number of magnitude 4s distributed over several different faults with no large quakes associated with them, he said.
“Now we have as many as 13 different fault zones in Oklahoma with magnitude 4s occurring on them this year alone,” McNamara said. “And so just from the behavior of the Prague sequence, any one of these looks like it could produce a 5- or 6-magnitude earthquake, so we’re very concerned about a number of these fault zones.”
The ‘clear’ case of Cushing
McNamara published a peer-reviewed paper on the Cushing case a month ago in Geophysical Research Letters. A supplemental to his paper explains that two intervals of temporary injection-well shutdowns in October 2014 “are clearly observed as strong variations in the daily microseismicity rate” that took place 17 days after each change in operation.
“It’s pretty clear that it can be managed. I think Cushing is a great example of that,” McNamara said. “There were two magnitude 4s in October of 2014, and the (Oklahoma Corporation Commission) shut down several wells in the region and the seismicity dropped off immediately, so that one is about as clear as it gets.”
This year, nearby quakes of 4.5, 4.1, 3.5 and 3.0 magnitudes in September and October redirected the spotlight back onto Cushing. The latest seismicity prompted the Corporation Commission to direct four wells to cease operations, while nine others were to drop injection volumes.
Experts are waiting to document the effects, and McNamara said seismicity “sure seems to be dropping off again.”
“Rather than eject into two active faults immediately beneath the largest oil storage facility in the world, take some of that volume and distribute it into the regions that are less active,” McNamara said. “That’s sort of the general recommendation that USGS has at this point.”
Relief via mitigation or market adjustments?
The Corporation Commission has issued broad directives to 558 well operators in 21 counties in 2015 to plug back depths of wells injecting below the state’s deepest geologic formation or reduce volumes. The agency also has taken micro approaches to several areas, tightening regulations on specific wells near earthquake-riddled areas such as Crescent, Guthrie-Edmond, Cushing, Medford, Fairview and Cherokee.
And the state might be experiencing a modicum of relief — believe it or not.
Jeremy Boak, director of the Oklahoma Geological Survey, also believes that society can manage the hazard. But he isn’t sure how much of a recent downward trend can be attributed to mitigation efforts. In fact, Boak said, if there is a sustainable trend appearing, then it might be driven more by falling commodity prices resulting in less oil production rather than by stricter regulations imposed by the Corporation Commission.
The 90-day average of magnitude-2.8 or greater earthquakes is down about 25 percent from a July peak of about 4.8 quakes per day, Boak said. But that rate appears to be ticking upward again.
Boak cautioned that it’s also not known whether the trend is or was simply a lull, or how much — if any — the rate might ramp back up.
“The preliminary data we’ve looked at for a subset of wells suggests that injection is down over the course of this year, and that could be affecting earthquakes,” Boak said.
Recent quakes highlight faults unknown to scientists
McNamara noted that the recent magnitude-4.7 temblor near Cherokee on Thursday and the 4.3 close to Fairview on Nov. 15 illustrate yet another challenge. Both appear to be on faults previously unknown to the U.S. Geological Survey.
He said unmapped faults present difficulties in determining the maximum magnitudes that can occur on them and where the quakes could strike, as well as whether they are isolated or connected to larger fault structures.
Industry could play a role with its “very good” 3-D models used to locate oil and gas deposits, which could help map fault structures, McNamara said. The hangup is that the information is mostly proprietary, he said, and sharing it could allow other companies to exploit the data.
There has been progress on that front with several projects, McNamara said, including a fault database industry shared several months ago.
“The U.S. government doesn’t want to take your oil and gas revenues. We just want to know where the faults are,” McNamara said. “So if we could somehow improve data sharing to learn how to mitigate this better would be great.”
Industry warns of economic tolls
A report released last week by an oil and natural gas producers organization indicates that the industry is collectively acknowledging some ownership of the problem, although it warns that “states should avoid drastic measures that are fueled more by politics than sound science, including blanket bans on injection wells.”
Energy In Depth, a campaign of the Independent Petroleum Association of America, produced the report. The 19-page document cautions against policies that “ban or seriously restrict oil and natural gas development” as action that would place hundreds of thousands of people out of work, also eliminating millions of tax dollars to local and state governments.
“For many in Texas and Oklahoma, this ‘solution’ would be far worse than the problem it was designed to fix,” the report states.
Energy In Depth’s report also lists several efforts it says industry has undertaken, including investment of $35 million since March in activities to reduce quake risks; providing information on deep geological formations and previously unmapped faults; supporting the Oklahoma Corporation Commission’s “traffic light” regulatory approach; and voluntary compliance in reducing volumes or shutting down wells in the commission’s areas of interest.