The Fuse

Separating Fact from Fiction on Oklahoma Earthquakes

by R. Kress | January 25, 2016

The proliferation of Oklahoma earthquakes rightfully has regulators, lawmakers, residents and geologists concerned, and there’s little doubt that wastewater injection from fracking operations is playing a role in the state’s increased seismic activity. The State of Oklahoma is now telling oil and gas companies to reduce their wastewater injections at dozens of disposal sites, but a larger-scale clampdown remains to be seen. As legislators debate whether or not to impose a tax on injected fluids per barrel that would compensate residents who’ve seen earthquake-related damages, misconceptions remain about the cause, the scope and the solutions for this problem.

Myth: Oklahoma is now the earthquake capital of the United States.

While it’s a catchy tagline—most recently employed by the Associated Press—geologists aren’t in agreement. Dr. Jeremy Boak, Director of the Oklahoma Geological Survey tells the Fuse to note that Alaska, part of the continental (if not contiguous) U.S. has many more earthquakes than Oklahoma. California, while seeing fewer earthquakes, experiences much stronger ones—Boak estimates that California released ten times the amount of seismic energy that Oklahoma did in 2015.

“Oklahoma is the small earthquake capital of the U.S.,” Boak clarifies. “We have a preponderance of smaller earthquakes and they appear to be a feature of this induced seismicity.”

Myth: Oklahoma’s earthquakes are caused by fracking.

Experts say there is an important distinction to be made between saying that hydraulic fracking causes earthquakes and saying that the disposal of fracking wastewater causes earthquakes.

“There are a very small number of actual ‘frack quakes’—earthquakes that happen during or immediately after a frack job. But these are not that kind,” cautions Boak.

Instead, he explains that the oil and gas being produced from fracking comes to the surface along with large volumes of formation water—usually ancient ocean water. At a facility on the surface, operators typically separate the water from the oil and gas so the latter two can be brought to market. The remaining water, however, has a very high salt content and may also be contaminated by heavy metals or the oil and gas itself after centuries or even millennia sitting in the rock formation. That water must then be disposed of.

Boak estimates that for every barrel of oil that can be produced, operators are left with 10 to 15 barrels of wastewater.

In Oklahoma, the oil and gas is being extracted from wells with a high water to hydrocarbon ratio. Boak estimates that for every barrel of oil that can be produced, operators are left with 10 to 15 barrels of wastewater. That leaves a big disposal job that continues through the life of the well, long after drilling and hydraulic fracturing are complete. For years, in Oklahoma, operators had been injecting that wastewater into the Arbuckle Group, which is the deepest sedimentary rock unit in most of Oklahoma. Over time, the steadily increasing volume raised the pressure in the Arbuckle and in the deep basement, where most of the active faults lie, causing earthquakes.

“The Arbuckle Group took a lot of water for a long time until we put so much in that it started causing earthquakes,” Boak explains. “It’s not a lot of flow into the basement but it’s transmitting a pressure wave. And the slight increase in pressure is enough to make it easier to move.”

Boak compares the shift to a puck on an air hockey table. Without the air flow, the puck barely moves. With just a small change in the air below it, however, it slides with ease.

While it is a misconception that fracking itself causes earthquakes, it is true that without the widespread use of the technique, the eventual induced earthquakes caused by produced water disposal would be avoided altogether. Boak, however, says that this is a “specious argument.”

“Yes, it’s true. If you shut down all fracking, you wouldn’t have the earthquake problem. But you would then shut in a whole lot of places that don’t have the earthquake problem, and you’d lose huge amounts of production,” Boak says, noting that the Bakken formation is also hydraulically fractured, but requires less wastewater disposal, has seen few to no induced earthquakes.

Myth: Without induced earthquakes, Oklahoma would have no seismic activity.

Unlike California or Japan or Hawaii, Oklahoma does not come to mind first as an area of natural seismic activity. However, this is a popular misconception.

“Geologists have identified a fault in Southern Oklahoma that ruptured in prehistoric times—more than 1000 years ago, but not much more. It produced an earthquake with a magnitude around 7.0,” explains William Ellsworth, a professor with the Stanford Center for Induced and Triggered Seismicity. “A recurrence of an earthquake that size would be a very serious event and we know that in parts of [Oklahoma], there are faults capable of producing large earthquakes.”

Both Boak and Ellsworth note that an increase in the number of small earthquakes also boosts the probability of a larger earthquake occurring—and it doesn’t seem to matter if those small earthquakes are induced or natural. Regardless, Ellsworth suggests that Oklahoma residents educate themselves in earthquake preparedness.

“Not knowing the very simple things can have very tragic consequences,” Ellsworth says. “Running out of a building in an earthquake in Oklahoma is the wrong thing to do. Public education could play a very big role in protecting [people] in a very strong earthquake.”

Myth: The straightforward solution is to halt fracking and wastewater disposal altogether.

Even if state regulators were able to put a total end to all wastewater disposal operations today, the quakes might continue all the same.

“If you shut it in completely, right away, you might get more earthquakes,” Boak notes. “Because then, you’ll get a negative pressure pulse moving out in these areas. Some of these earthquakes we’re now seeing are in areas where we’ve actually shut in injection. That might be one type of response.”

Ellsworth also notes that a seismic hazard will remain, even with positive changes to industry practices.

“From an earth sciences perspective, finding ways that the fluids can be disposed of without raising pressure in the basement over a large region is the goal,” Ellsworth says. “We don’t know how the hazard will evolve with time. Even if all the injections stopped tomorrow, the pressure is already underground and it would take some time to dissipate.”