Shaking it up and Shutting Wells Down

On Saturday at 7:02 am, a 5.6 magnitude earthquake shook an area northwest of Pawnee, Oklahoma, roughly 55 miles northwest of Tulsa. Within hours, Governor Mary Fallin declared a state of emergency and ordered the shutdown of 37 wastewater disposal wells in a 500 square miles area near the earthquake’s epicenter.

Oklahoma has thousands of wastewater disposal wells. When oil and gas are extracted from the earth, salty water comes up along with the fuel and the water is often injected back underground.

Seismologists are concerned that the recent uptick in quakes (from 1.5 yearly in 2008 to a current rate of 2.5 daily) could be caused by this high-pressure injection. It seems, as wastewater permeates rock formations, it can affect interfaces along faults, and can allow them to shift.

Last year, seismologists at Stanford University published a study linking disposal wells to seismic instability of the Arbuckle formation. The study found that “…wastewater disposal is increasing the pore pressure in the Arbuckle formation, the disposal zone that sits directly above the crystalline basement, the rock layer where earthquake faults lie. Pore pressure is the pressure of the fluids within the fractures and pore spaces of rocks at depth.”

In an effort to minimize further seismic activity around the fault line, in 2015 the State of Oklahoma ordered operators of some disposal wells to reduce the volume of wastewater injected.

Fallin’s well shutdown order was part of her state of emergency declaration. Rather than wait for evidence about the link between seismic activity and wastewater wells, she took action. In addition, she asked state agencies to work with EPA to develop a course of action for disposal wells in an additional area of 211 square miles in Osage County as a precaution.

“This is the quickest action we’ve taken after an event,” said Matt Skinner, spokesman for the Oklahoma Corporation Commission, which oversees the state’s oil and gas activity.

Meanwhile, the US Geological Survey is working to determine whether Saturday’s earthquake was specifically triggered by the underground disposal of wastewater. It will continue to process seismic data in the coming days and weeks in an effort to address this question.

“Without studying the specifics of the wastewater injection and oil and gas production in this area, the USGS cannot currently conclude whether or not this particular earthquake was caused by industrial-related, human activities,” the USGS said in a statement. “However, we do know that many earthquakes in Oklahoma have been triggered by wastewater fluid injection.”