Oklahoma ordered the shutting down of 37 wells after a magnitude 5.6 earthquake in Oklahoma on Saturday has again focused attention on the ramifications of disposing wastewater from oil and gas field deep underground. The United States Geological Survey (USGS) said the quake happened at 7.02 a.m. in north-central Oklahoma, on the fringe of an area where regulators had stepped in to limit wastewater disposal. The shallow quake occurred nine miles northwest of Pawnee.
Five months ago, U.S. officials warned Oklahoma that the underground injection of drilling’s wastewater was linked to an increase in earthquakes in the state. Parts of the state are now as likely as California to suffer from tremors (see “Fracking-related quakes make central U.S. as vulnerable as California to tremor damage,” HSNW, 30 March 2016).
There are about 4,200 total wells across the state, with about 700 in a 15,000-square-mile “area of interest” in the area that includes the epicenter of Saturday’s temblor, near Pawnee.
Experts note that the significant increase in the number earthquakes measuring 3.0 or higher in Oklahoma has been linked to the practice of underground disposal of wastewater from oil and natural gas production.
The New York Times reports thousands of earthquakes have hit Oklahoma in recent years. Most have been imperceptible, but the number that can be felt — generally of magnitude 3.0 and higher — has risen significantly. Only three earthquakes of that size or stronger were recorded in 2009. Last year, the state had 907 such quakes. So far this year, there have been more than 400.
Many seismologists argue that the cause of the quakes is the high-pressure injection of wastewater from oil and gas wells, both conventional and hydraulically fractured, or fracked. Under pressure, the wastewater migrates into rock formations, altering stresses along old faults and allowing them to slip.
A report from the Oklahoma Geological Survey also found a connection between underground disposal of wastewater and tremors.
Saturday’s earthquake led the Oklahoma Corporate Commission to order thirty-seven wells in an area around the epicenter of the quake of 514 square miles to shut down within seven to ten days.
“All of our actions have been based on the link that researchers have drawn between the Arbuckle disposal well operations and earthquakes in Oklahoma,” commission spokesman Matt Skinner said Saturday.
“We’re trying to do this as quickly as possible, but we have to follow the recommendations of the seismologists, who tell us that everything going off at once can cause an [earthquake].”
The commission had already asked producers to reduce the volumes of wastewater disposal.
Oklahoma’s economy is heavily dependent on energy production, which accounts for one in every four jobs in the state.
The Oklahoma Department of Transportation (ODOT) said that none of the utilities, pipelines, or fuel infrastructure in the area had major damage.ODOT said it had inspected 180 state bridges within a 30-mile radius of the epicenter and reported minor cosmetic damage to two structures, but all are open and safe for travel.
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