State agencies react to weekend earthquake

Feb. 5—The Oklahoma Geological Survey said aftershocks from the Feb. 2 magnitude 5.1 earthquake are expected as state officials over the weekend suspended several disposal wells operating near the quake's epicenter.

According to OGS, the earthquake occurred at 11:24 p.m. Feb. 2 with the epicenter located approximately five miles northwest of Prague.

The United States Geological Survey's "did you feel it" map shows the quake was felt as far away as St. Louis, Missouri, Little Rock, Arkansas, and Dallas, Texas.

"There were reports of strong shaking in the immediate area and it was widely reported as being felt statewide, including the Oklahoma City and Tulsa metro areas," OGS said in a statement released over the weekend.

OGS said due to the likelihood of aftershocks, people around the area should take proper precautions should another strong earthquake occurs.

"The seismic hazard remains high in the area," OGS said in its release. "Citizens should secure valuables that might shake during possible strong aftershocks and practice drop, cover, and hold on in the event of damaging events."

The agency said the earthquake occurred in the same area as the 2011 M5.7 that was identified as having been inducted by wastewater disposal activities.

"We will continue to monitor the seismicity and provide assistance to the Oklahoma Corporation Commission, other state agencies, and the public," said OGS in the statement.

OCC on Feb. 3 ordered the shutdown of "all disposal wells that are permitted to dispose into the Arbuckle formation and are in an area within 10 miles" of the epicenter of the earthquake with the completion of the shutdowns to be completed by Feb. 17.

A map provided by the agency shows eight disposal wells fell within the 10-mile radius.

"The gradual shutdown process is necessary to avoid sudden pressure changes that could result in more seismic activity," the OCC said in a press release. "It should be stressed that this action is an initial response. Further study may result in new directives."

Information from the OCC shows that well completion operations in Oklahoma must follow a seismicity response plan related to potential seismicity within 3.1 miles of an operation.

Operators shall implement a seismicity response plan if an earthquake of 2.0 magnitude, but less than 2.5 magnitude is detected within the 3.1-mile area around a well bore.

If the magnitude is between 2.5 magnitude and 3.0 magnitude and the operator has not initiated its seismicity plan, the operator shall pause operations for six hours and a technical conference call is to be held with the Induced Seismicity Department.

If the operator was operating under an active plan, then a conference call is to be held with the ISD regarding procedures and any steps deemed necessary.

A six-hour pause is to be done by an operator for any earthquake between 3.0 magnitude and 3.5 magnitude. A conference call is to be held with the ISD staff and upon agreement, the operator will be permitted to resume with a revised completion procedure.

With any earthquake greater than a 3.5 magnitude, the operator shall suspend operations immediately and an in-person technical conference is to be held with the Oil and Gas Conservation Division of the OCC to examine whether operations can resume with changes.

Thousands of earthquakes have been recorded in Oklahoma in recent years, and many have been linked to underground injection of wastewater from oil and natural gas production.