The oil wastewater disposal well near the epicenter of Oklahoma's largest recorded earthquake was drilled too deep, a mistake that some think can lead to earthquakes.
New Dominion LLC, the Tulsa-based producer that owns the well, recently sought and received state approval to make the well shallower by "plugging it back."
But New Dominion said that doesn't mean its Wilzetta disposal well is connected to the magnitude-5.7 earthquake in November 2011 near Prague, Okla.
"New Dominion LLC categorically and expressly denies that its Wilzetta salt water disposal well had anything at all to do with the Prague earthquake in 2011," company attorney Fred Buxton said in an email exchange.
But state officials and seismologists say drilling into granite "basement" rock creates a path for wastewater injected into disposal wells to reach faults and cause earthquakes. The fluid gets into the fault and changes the pressure, and the rocks slip (EnergyWire, May 13).
"Anytime you're going into the basement, that's an enhanced risk factor," said Katie Keranen, a Cornell University seismologist who has extensively studied Oklahoma earthquakes.
The Oklahoma Corporation Commission, which regulates oil and gas activity including disposal, has been moving to make sure wells in earthquake-prone areas aren't injecting into basement rock.
In a March 12 letter to New Dominion, commission officials told the company to prove that five of its wells, including the Wilzetta, were not drilled into basement rock.
"The commission needs to be confident these wells are not injecting into basement," wrote Tim Baker, director of the commission's Oil and Gas Conservation Division.
Commission records show that one of the other four wells is "in communication" with the basement. The status of the other three is unclear.
Some geologists at the Oklahoma Geological Survey (OGS) had suspected since 2007 that New Dominion's operations were causing earthquakes. But the agency did not go public with the theory and instead accepted thousands of dollars worth of seismic equipment from the company. For years, they told the public the quakes were natural (EnergyWire, April 27).
Last month, OGS ended years of wavering on the topic when it issued a statement saying the state's surge in earthquakes was "very likely" due to disposal of wastewater from oil and gas.
The November 2011 earthquake was centered east of Oklahoma City, near the city of Prague. It was even closer to the Wilzetta well, which shares the name of the fault that ruptured. The quake damaged hundreds of buildings, destroyed 14 homes and injured two (EnergyWire, July 24, 2012).
Several homeowners are currently suing New Dominion in connection with the quake.
New Dominion's Buxton said the decision to plug the well back does not mean it's "too deep." He said the company is simply complying with commission orders to ensure wells are no deeper than 100 feet from the bottom of the Arbuckle formation.
The granite basement in the area of the Wilzetta well starts at 6,828 feet. Documents New Dominion submitted to the state, obtained by EnergyWire through an open records request, show that the well was drilled to a depth of 7,185 feet.
New Dominion told the state the well would be much shallower than that -- 6,725 feet -- when it sought state approval to drill it in 1999.
The well was permitted to dispose of wastewater in the Arbuckle formation, a deep layer that accepts a lot of fluid. Deeper is generally better because the rules covering injection wells are meant to prevent groundwater contamination. The deeper the well, the farther from groundwater.
Corporation commission officials say they never permitted wells in the basement. But they didn't check closely, because their main concern was groundwater contamination. Now that earthquakes are a problem, they are going back and looking at whether wells were drilled too deep.
Beneath the Arbuckle in most places is "basement" rock. Oil and gas officials say that injecting into basement rock creates a greater risk of causing earthquakes than injecting into shallower layers.
In 2014, Oklahoma had 585 earthquakes of magnitude 3 or greater, three times more than California. So far this year, it has had more than 330 such quakes. If the shaking continues at the same rate, there would be more than 900 by the end of the year.