Oklahoma is a seismically active state crisscrossed with thousands of natural fault lines. But seismic activity has spiked over the past five years, leading scientists, regulators, oil and natural gas industry representatives and the general public to question what is different today — if anything — and what could be causing the rumblings.
The number of earthquakes measuring magnitude 3.0 or greater has jumped from an average of less than five a year to about 40 a year for the past five years and more than 200 so far in 2014, according to the Oklahoma Geological Survey.
Some researchers have attributed the swarm to natural causes. Others have pointed largely to the oil and natural gas industry, specifically at its practice of disposing of produced water by pumping it deep below ground. Others say the unusual swarm likely is a combination of factors.
One theory is that the state’s recent rumblings have natural origins.
Oklahoma — along with much of the central United States — is home to thousands of faults and has a history of quakes.
Earthquake swarms also are known to have occurred in other parts of the country. Before joining the Oklahoma Geological Survey, Oklahoma Geological Survey seismologist Austin Holland worked for the Idaho National Laboratory, where an earthquake swarm was recorded in an area without oil and natural gas activity.
“We had several thousand earthquakes in Idaho over a couple of years. Then it went quiet,” Holland said. “It was quiet before and after. Clearly the seismicity rates don’t remain constant over time. There were no human activities that could have affected that in any way.”
Continental Resources Inc. geologist Glen Brown has drawn a connection between the world’s largest earthquakes and seismic activity in Oklahoma.
Oklahoma has a history of seismic activity. Five of the state’s 15 largest recorded earthquakes occurred before the ongoing swarm, including the previous record-holding magnitude 5.5 in El Reno in 1952.
Click image for larger version
Half of the world’s recorded magnitude 8.0 or greater quakes have happened over the past 10 years. The other half occurred during the 1950s. Both times of great seismic activity in other parts of the world have corresponded with quakes in Oklahoma, Brown said.
“This is compelling data. What’s happening in Oklahoma appears to be tied to global activity,” said Jack Stark, senior vice president of exploration at Continental Resources.
University of Texas seismologist Cliff Frohlich, however, dismissed the connection.
“I’m unaware of any evidence worldwide that there has been a change in earthquakes in the ’50s or presently,” said Frohlich, a senior research scientist at the University of Texas’s Institute for Geophysics.
Brown also has pointed to a swarm of earthquakes in northern Mexico over the past few years, including swarms in Chihuahua, Monterrey and Nicah, which are all hundreds of miles from oil and natural gas activity. While Oklahoma has experienced 20 magnitude 4.0 or greater over the past few years, Nicah has experienced 49, Brown said.
“What’s going on in Nicah is phenomenal,” Brown said.
Other possible explanations have to do with drought and lake and aquifer levels. Scientists have noted that earthquakes were created when Lake Mead was filled following construction of the Hoover Dam. Some researchers in Oklahoma and in other parts of the world are studying whether filling or draining underground aquifers could have a similar effect.
“Many times, the filling of dams has caused earthquakes because of the weight you’re putting on the earth’s crust,” said William Fleckenstein, professor and interim department head at the Colorado School of Mines.
Oklahoma and other Western states are three years into a drought that has strained aquifers, lakes and other water systems.
The U.S. Geological Survey has said man-made activity likely has at least contributed to the Oklahoma quakes.
“We’ve statistically analyzed the recent earthquake rate change and found that they do not seem to be due to typical, random fluctuations in natural seismicity rates,” USGS seismologist Bill Leith said in a May report.
Researchers from the U.S. Geological Survey, Cornell University, the University of Texas, Oklahoma State University and other sources have listed water disposal wells as a potential cause or contributor to the quakes.
However, oil and natural gas industry representatives point out that wastewater disposal practices are largely unchanged over at least the past 70 years. The average oil well in Oklahoma produces about 10 barrels of saltwater for every barrel of oil. That water — which is about four times saltier than the ocean — is piped or trucked to a disposal well where it is pumped deep underground.
The research largely has dismissed hydraulic fracturing, or fracking, as a concern, instead pointing to the way the industry disposes of the water that is naturally produced along with the oil and natural gas.
Cornell University professor Katie Keranen has concluded at least part of the state’s ongoing swarm to a series of particularly high-volume disposal wells in eastern Oklahoma County.
A former University of Oklahoma professor, Keranen’s latest research indicates that wastewater disposal wells can cause quakes more than 18 miles away, far more than the previously understood range of about three miles. With that range and pressure, the disposal wells could be responsible for the earthquake swarm the state has experienced over the past three years, the report published in the journal Science stated.
“The disposed fluids are capable of contributing to the seismic activity,” Keranen said. “These wells are capable. That doesn’t exclude anything else from contributing, but we have no reason to think these are tectonic. They don’t match tectonic activity in other areas. It does seem these are just linked to wastewater. Our research focuses on wastewater and shows it is sufficient.”
The study focused on 89 disposal wells in central Oklahoma. The report stated that four high-volume wells could have contributed to up to 20 percent of the recent outbreak.
“They might consider drilling more wells with less pressure each,” Keranen said.
Fleckenstein, however, said that in his experience, disposal wells have a limited reach.
“The injection well has to be pretty close to the epicenter,” he said. “The change in pressure doesn’t extend out very far.”
Oklahoma is dotted with nearly 12,000 water injection and disposal wells. The industry has used the technique in the state for at least the past 70 years.
In most cases and in most areas, disposal wells do not pose a problem, Fleckenstein said.
“The big question is going to be the resulting stress,” he said. “What pressure is there? Is the area experiencing higher and higher pressure, or is the fluid leaking off into the surrounding rock? In many cases, it’s like having a big fire hose pour into the ocean.”
In other cases, however, rock formations are compartmentalized, Oklahoma State University researcher Priyank Jaiswal said.
“If you take an empty compartment and start filling it, over 50 years or so, we don’t know what parts have filled in,” said Jaiswal, assistant professor of seismology at OSU’s Boone Pickens School of Geology. “Maybe we are trying to inject into compartments that are already full.”
While scientists are eager to gain a better understanding of the earthquake swarm, Jaiswal said it is important not to overreact.
“One in every three Oklahomans works in the energy industry. Should we stop it? Not at all,” he said. “Go to a state like California where earthquakes are common. They learn to live with them. Are earthquakes good? No. But there is a fine line there because there is a lot of economic incentive within oil and gas in Oklahoma.”
Click image for larger version
Still, Jaiswal said studying and better understanding the Oklahoma quakes is a matter of national security.
“I think we are reacting appropriately,” he said. “To close our eyes on this would be sin. There is a phenomenon that is directing this. Either we stop this phenomenon or learn to live with it. In either case, we have to be proactive.”
Combination of factors
Others, however, say a combination of factors is likely the cause.
Texas’ Frohlich has studied the relationship between oil and natural gas activity and earthquakes for nearly three decades. He has looked at the quakes associated with oil and natural gas drilling in the Fort Worth area, in west Texas and in Arkansas and said water disposal wells likely have at least something to do with Oklahoma’s ongoing earthquake swarm.
Frohlich compares the relationship between disposal wells and earthquakes to smoking cigarettes and developing lung cancer.
Statistics show that people who smoke are more likely to develop lung cancer. But some people smoke and never develop lung cancer while others develop lung cancer even though they didn’t smoke.
“It’s very difficult to say this earthquake was caused by that well, but when you have water injections in areas where the faults and the rocks line up right, you’re likely to have increased rates of earthquakes,” Frohlich said.
“What I’ve learned is that in a lot of situations in Texas, it certainly looks like human activity is causing earthquakes to happen. What you’d like to find is a silver bullet that if you don’t inject over 100,000 barrels you won’t have earthquakes, but there doesn’t appear to be a silver bullet. In some cases there are earthquakes, and in others there are not.”
While Frohlich’s research points to possible human involvement in earthquakes, he said he welcomes other researchers who reach different conclusions.
“Science is a dialog,” Frohlich said. “It mostly happens in publications. A researcher writes a paper and submits it to a peer review process. Someone else will see the paper and try to poke holes in the theory.”
Skepticism is highly valued in the field.
“If a smart person walks into my office and says, ‘This statement is true because I’ve studied it my whole life,’ my first thought is you’re probably wrong,” Frohlich said. “There’s probably something you didn’t think of.”
The one thing all the scientists seem to agree on is that they need more data, more information.