The Oklahoma Corporation Commission said Friday it is placing more than 200 oil and natural gas wastewater disposal wells under scrutiny as the regulatory agency investigates whether the wells are triggering earthquakes in the state.
The main focus of the action is on high-volume disposal wells in a geologic formation known as the Arbuckle that research shows hold the highest potential risk for triggering earthquakes, said Tim Baker, director of the agency's Conservation Division. The Arbuckle is the state's deepest formation and encompasses most of the state.
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The Oklahoma Geological Survey issued a report in April that said it is "very likely" most of the state's recent earthquakes were triggered by the subsurface injection of wastewater from oil and gas drilling operations.
Geologists historically recorded an average of 1.5 earthquakes of magnitude 3 or greater each year. The state is now recording an average of 2.5 magnitude 3 or greater earthquakes each day, according to geologists.
"There is still no issue more important to us, and to thousands of Oklahomans, than this," Baker said. "There has been progress made, and we know far more than we did, but there is much more to be learned and more actions to be taken as we go forward based on the latest data and research."
The commission issued a directive in March that covered more than 300 disposal wells that inject into seismically-active areas in 21 of Oklahoma's 77 counties. The latest directive expands the size of the areas covered and applies to 211 more wells.
Baker said seismic activity has occurred in some areas that don't have high-volume, deep disposal wells, including northern Oklahoma County and southern Logan County.
"Operators of low-volume Arbuckle disposal wells in the area that have long been proven to be operating at the proper depth have now voluntarily shut down their wells to aid research efforts," Baker said.
Under the latest directive, operators will have until Aug. 14 to prove they are not injecting below the Arbuckle formation. The commission said there is broad agreement among seismologists that disposal below the formation poses a potential risk of causing earthquakes because it puts the well in communication with the "basement" rock.
The commission said that since March, 124 Arbuckle disposal wells have reduced their depth and 16 are in the process of reducing depth. In addition, 54 wells are limiting their volume to less than 1,000 barrels a day, 25 have cut their injection rate in half and 37 are not injecting.
The commission has received a $200,000 grant from the Oklahoma Secretary of Energy and Environment to help implement the latest directive.
The action was welcomed by Gov. Mary Fallin and an industry spokesman.
"Reducing seismic activity requires a cooperative effort," Fallin said. "The energy industry understands the need to protect homes and businesses and is voluntarily providing the Oklahoma Geological Survey and the Governor's Coordinating Council on Seismic Activity with data and research assistance."
Chad Warmington, president of the Oklahoma Oil & Gas Association, said results of the commission's previous actions are encouraging.
"We believe this new directive will have a positive impact as well," Warmington said.