Stillwater could be near the epicenter of potentially large earthquakes.
Chris Hartnady, a South African geologist, said in a study released in March that part of Oklahoma is in danger of a larger earthquake.
The area of risk is positioned near Guthrie, Langston and Stillwater, according to the study. The distribution of recent epicenters reveals possible hidden faults, which may be oriented for re-activation, and earthquakes greater than magnitude 5 could shake the region on a weekly basis by the end of 2015, according to the study.
“If a major part or the whole of the GLS (Guthrie, Langston and Stillwater) structure is accidentally re-activated in a low-stress-drop regime by wastewater injection, it is capable of generating a significant earthquake in the range (magnitude) 5.5-6.5 or greater,” Hartnady said in the study.
Central Oklahoma has seen a rapid increase of earthquakes greater than magnitude 3 since 2012.
There were 40 earthquakes magnitude 3 or greater in 2012, 111 in 2013, 611 in 2014 and about 600 so far in 2015, according to the United States Geological Survey.
“As long as we have seismicity, you can certainly expect us to keep going,” said Matt Skinner, Oklahoma Corporation Commission spokesman.
The current rate of Oklahoma earthquakes is about 600 times greater than Oklahoma’s historical averages, according to the Office of the Secretary of Energy and Environment.
The Oklahoma Corporation Commission on Aug. 3 instructed operators of 23 wastewater disposal wells to reduce the volumes they’re injecting by 38 percent, according to an Oklahoma Corporation Commission document.
Skinner said the total amount of produced water injection in the region would drop by 2.5 million barrels, or 110 million gallons.
He said Oklahoma has become the centerpiece for induced seismicity research.
“In natural seismicity, statistical models show that the more earthquakes you have, the greater the likelihood of you having a large earthquake,” Skinner said. “No one is quite sure if induced seismicity follows that same pattern, but certainly we act out of that concern.
“We’re going to assume that that is a possibility and take action accordingly.”
The 23 injection wells, which are located in Oklahoma and Logan counties, span a region that’s at risk for further increases in seismicity, according to an Oklahoma Corporation Commission document.
Logan County is between Payne and Oklahoma counties, and the area of risk begins about 10 miles south of Stillwater, and reaches to northwest Oklahoma City.
Produced water is a byproduct of hydraulic fracturing. Water naturally coexists with underground oil and gas reserves, and that water is extracted along with the fuel. Companies normally separate the water after extraction and dispose of it by injecting it back into the earth through the use of injection wells, according to the Office of the Secretary of Energy and Environment.
“We know a lot more than we did a year ago when it comes to induced seismicity and about what’s underground in Oklahoma in terms of the faults,” Skinner said. “Based on the data and based on the evidence, we feel that a volume cutback is justified.”
A magnitude 5 earthquake can cause considerable damage, and a magnitude 6 earthquake can cause severe damage.
Mark Zoback, Stanford geophysicist, published a study June 18 that linked Oklahoma’s increased seismicity to increases in the rates of saltwater injection.
“These formations appear to be in hydraulic communication with potentially active faults in crystalline basement, where nearly all the earthquakes are occurring,” Zoback said in the study. “Although most of the recent earthquakes have posed little danger to the public, the possibility of triggering damaging earthquakes on potentially active basement faults cannot be discounted.”
Chad Penn, OSU associate professor, said deep well injection is the easiest, cheapest way to dispose of produced water.
“The problem is, they've been injecting it excessively deep, with excessive volumes, in the wrong geology,” Penn said. “And because of that, that's why we have earthquakes right now.”
He said it’s a complicated issue that researchers and officials don’t fully understand, but they understand the trend.
“With the earthquakes, it's ultimately a waste management issue,” Penn said.
Penn said it’s difficult to safely dispose of water-based mud, which is the industry’s term for used drilling fluid, because it’s too salty.
Drilling fluid is used to lubricate drills and to seal the shaft.
He said if companies don’t dispose of water-based mud properly, then they run the risk of salinizing groundwater or soil.
Penn said plants in overly salinized soil could show drought symptoms regardless of having adequate freshwater sources.
“The problem is that it increases the osmotic potential in the soil, which means it makes it harder for the plant to take up water,” Penn said. “So you could have lots of water in the soil, but if there's excessive salts, the salt holds on to the water so strongly that the plants can't get it.”
He said companies often bury the salty mixture in reserve pits lined with a material to contain waste, which is a bad idea because they could leak.
Penn said the safest option is to thinly spread water-based mud across many acres, which reduces the long-term effects on soil fertility.
He said salinization is bad because it could render soil useless, and it could ruin groundwater reserves that many Oklahomans depend on.
In a 2013 study, Swiss geophysicist Max Wyss said the public needs to be well informed about potential earthquakes of great magnitude
He references a 2011 magnitude 6.3 earthquake that killed 309 people in L’Aqulia, Italy, after the region was shaken by an ongoing earthquake swarm.
“They should be told quantitatively the consequences of the reasonably worst case and be motivated to prepare for it, whether or not it may hit the present or the next generation,” Wyss said in the study.