OKLAHOMA CITY – The magnitude-4 earthquake that rattled Cushing shortly before noon Tuesday occurred three weeks prior to a legislative study on state monitoring of data arising from wastewater injection wells.

The examination is a consolidation of studies requested by state Rep. Cory Williams, D-Stillwater, and state Rep. Jason Murphey, R-Guthrie.

Murphey proposed a study of injection well data monitoring activities performed by the Oklahoma Corporation Commission, which regulates oil and gas production in this state.

Williams requested a study of the potential subterranean effects of oilfield activity, particularly whether “fracking” and high-volume wastewater disposal wells associated with oil and gas production are contributing to the spate of tremors in central Oklahoma. “We have been having a swarm of earthquakes in our area, and I’m fielding a lot of inquiries from constituents who want to know what, if anything, the State of Oklahoma is doing about it,” the Stillwater Democrat said in mid-July.

The U.S. Geological Survey logged 17 temblors in the Stillwater area in the past 30 days. Besides the one two and a half miles southwest of Cushing on Tuesday, they included half a dozen north of Yale, two west southwest of Pawnee, one 8.7 miles north of Langston, and seven north, east and west of Stillwater.

House Speaker Jeff Hickman assigned the interim study to the House Committee on Utility and Environmental Regulation. Its members are: Rep. Colby Schwartz, R-Yukon, chairman; Rep. Mark McBride, R-Moore, vice chairman; Rep. Mike Christian, R-OKC; Rep. Lewis H. Moore, R-Arcadia; Rep. R.C. Pruett, D-Antlers; Rep. Mike Reynolds, R-OKC; Rep. Seneca Scott, D-Tulsa; and Rep. Weldon Watson, R-Tulsa.

The Corporation Commission has issued permits for approximately 4,500 disposal wells throughout Oklahoma, but many are not operated in any given year. Consequently, the number of active disposal wells is about 3,300 annually, according to Matt Skinner, the commission’s public information manager.

Payne County has approximately 6,700 oil and gas wells that are designated as active, plus 221 injection wells, Corporation Commission ledgers reflect. Of the injection wells, six are commercial disposal wells; 74 are enhanced recovery wells, which can include fracked wells; and the remainder are all wastewater disposal wells.

The Oklahoma Independent Petroleum Association reports that in some areas, water emerges from the wellbore along with oil and gas. Such wells typically produce 10 times as much water as hydrocarbons, the OIPA claims.

Among the enhanced recovery wells in Payne County: one used 638,000 barrels of wastewater in 2011 to produce oil, plus 595,600 barrels in 2012. Another Payne County enhanced oil recovery well operator reported using 2.7 million barrels of wastewater three years ago, 1.87 million barrels two years ago, and 3.7 million barrels last year.

Enhanced recovery is a method of improving production from old zones. “ER is not currently thought by seismologists to be a source of the strong earthquakes we’ve experienced,” Skinner said. “It’s an open, circular process that involves injection, recovery, and injection over and over again,” he explained. “It’s an operation that requires a loop, in and out from the same formation zone to the surface, in constant circulation.”

Disposal wells, though, are another matter. Several geologists and research scientists contend that disposal wells – particularly those accepting large volumes of wastewater, particularly if it’s injected under high pressure – have the potential to lubricate subterranean faults, triggering earthquakes.

Of the half-dozen commercial disposal wells (CDW) in Payne County:

Ÿ One accepted 180,000 barrels of wastewater in 2011 and the same amount in 2012, and 182,500 barrels in 2013. (A barrel is equivalent to 42 gallons, so 182,500 barrels equals 7,665,000 gallons of wastewater.)

Ÿ One CDW accepted 45,000 barrels (1.89 million gallons) of oilfield wastewater in 2011, and 24,500 barrels (1.029 million gallons) in 2012, and 38,800 barrels (1.6 million gallons) of wastewater in 2013.

Ÿ One was inactive in 2011, but received 65,340 barrels of wastewater (2.7 million gallons) in 2012 and 60,660 barrels (2.54 million gallons) in 2013.

Ÿ The three other commercial disposal wells were inactive in all three years.

Into one Payne County disposal well 1.7 million barrels of wastewater were injected in 2011, followed by 1 million barrels in 2012 and 626,971 barrels in 2013. One disposal well received a total of 1.9 million barrels of wastewater during those three years.

Another disposal well accepted 732,000 barrels of wastewater in 2011-13, and yet another Payne County disposal well received 108,000 barrels of wastewater, 4.5 million gallons, in each of the three years, Corporation Commission records show.

At least 21 injection wells in the county, and perhaps more, were inactive all three years.

All disposal wells in Oklahoma are required to have pressure meters, Skinner said. Operators of all disposal wells within six miles of a designated earthquake area are required to monitor their meters daily and report that data to the Corporation Commission. In addition, all wells injecting into the Arbuckle formation, regardless of whether the well is sited within a designated earthquake area, are required to be monitored daily, Skinner said.

The meters and the operations of those wells also are spot-checked by field inspectors from the Corporation Commission’s Oil and Gas Conservation Division. “We are averaging 7,000 to 10,000 Class 2 injection well inspections a year,” Skinner said. “Those inspections include checking for metered pressure, etc.”

Regulators said Oklahoma producers injected more than a billion gallons of oilfield wastewater underground in 2012.