Regulators in Oklahoma said an operator has voluntarily reduced completion operations at a well west of Oklahoma City after a series of small earthquakes rattled the area.

Spokesman Matt Skinner of the Oklahoma Corporation Commission (OCC), told NGI’s Shale Daily that Tulsa-based Citizen Energy II LLC reduced pressure and volumes at the McWhirter 1H-13-12 well in response to seismic activity that coincided with completion operations, which began a few days before the Thanksgiving holiday. The well near Yukon has two laterals.

“The seismicity issue,” he said, began on Nov. 20 “and then really ramped up on Thanksgiving,” Skinner said. Citizen Energy workers reduced operations, “but then they had several other events where they would cut back. They would start a new stage, have new problems and cut back…

“There were several actions involving several stages. Each time they started a new stage, it seemed that they would get a corresponding issue that they would have to deal with.” Skinner added that Citizen Energy had the well operating at various pressures and volumes, the lowest of which was 50%. Now, “they are definitely at reduced volume and pressure.”

Completion operations are scheduled to be finished by Tuesday (Dec. 5).

The U.S. Geological Survey (USGS) reported that a temblor measuring 2.5-magnitude struck at 4:55 p.m. CST on Nov. 23, Thanksgiving Day, about 4.4 miles south-southwest of Yukon. USGS said a 2.6-magnitude quake struck at 2:32 a.m. on Nov. 27 about three miles south-southwest of Yukon

Last June, Citizen Energy and Linn Energy Inc.formed a joint venture (JV), Roan Resources LLCm to accelerate development in Oklahoma’s Anadarko Basin. Specifically, the JV holds acreage within the emerging Merge prospect, as well as Oklahoma’s stacked plays, the STACK, the Sooner Trend of the Anadarko Basin, mostly in Canadian and Kingfisher counties, and the SCOOP, aka the South Central Oklahoma Oil Province. Yukon is in Canadian County.

The OCC and its Oil and Gas Conservation Division have attempted to mitigate induced seismic activity for the last two years. They have focused on wastewater injection wells targeting the Arbuckle formation, the state’s deepest, within a 15,000-square mile area of interest in the state.

Skinner said there are no disposal wells targeting the Arbuckle in the vicinity of the McWhirter well.

“The bulk of our seismicity is still linked to disposal into the Arbuckle formation,” he said. “But what we started to see when the SCOOP and STACK began to be developed was a pickup in small seismic activity that could not be drawn to Arbuckle disposal because there wasn’t any.”

Environmentalists seized on the news to posit that hydraulic fracturing (fracking) causes earthquakes.

“For years, the agencies responsible for regulating fracking have refused to confirm that fracking is contributing to the increase in earthquakes we’ve been experiencing in Oklahoma, despite all evidence to the contrary,” said Sierra Club’s Johnson Bridgwater, director of the Oklahoma chapter. “Finally, this acknowledgement that fracking is one of the causes of these earthquakes after all makes it clear that these claims have been completely disingenuous.”

Last month, researchers from theUSGS and Southern Methodist University studying seismic activity within two geologic regions in neighboring Texas said a series of earthquakes since 2009 were likely caused by human activity. They added that wastewater injected from oil and gas drilling targeting the Barnett Shale was a possible root cause for the quakes.

A study conducted one month earlier by researchers at the University of Colorado at Boulder found that a series of earthquakes in the Raton Basin, which includes southern Colorado and northern New Mexico, was also likely to have been triggered by wastewater disposal wells supporting oil and gas drilling in the region.