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More Injection Wells Halted After OK Quake
A Labor Day weekend earthquake in Oklahoma that was originally reported at magnitude 5.6 was upgraded late last week to a record 5.8, prompting the closure of a total of 54 wastewater injection wells in a state where seismic activity has skyrocketed in recent years.
The Sept. 3 quake shook north-central Oklahoma, with its epicenter in the town of Pawnee. It surpassed in the record books a 2011 temblor that the United States Geological Survey has deemed a 5.7 in magnitude. Seismic activity was rare in the state before 2010; there were just earthquakes of a magnitude greater than 3.0 measured in 2008. In 2015, that number had jumped to 900.
Linking Wells, Quakes
Both the state of Oklahoma and the U.S. Environmental Protection Agency have linked the increasing seismic activity to Class II injection wells, used to inject wastewater from oil and gas operations into the ground. Neighboring Texas is at odds with the EPA, with state officials denying that there is clear evidence that the injection sites have caused the increasing number of quakes in the region.
According to mapped data provided by the state of Oklahoma, the bulk of the quakes that have occurred in recent years have been centered around the north-central part of the state.
The bulk of the quakes that have occurred in recent years have been centered around the north-central part of the state. (Yellow and red represents seismic activity; blue dots represent Arbuckle formation injection wells.)
The Oklahoma Corporation Commission, which oversees oil and gas operations in the state, suspended activity at 37 Class II injection sites immediately after the Pawnee quake. On Wednesday (Sept. 7), the EPA ordered 17 more injection wells shut down.
Arbuckle Formation
Questions remain about the nature of the seismic activity in the region; oil and gas production, and even wastewater injection, have existed in the state since long before the sudden onset of seismic activity, and injection wells exist elsewhere with many fewer quakes measured.
United State Geological Survey
According to the USGS's first earthquake forecast depicting induced earthquakes, north-central Oklahoma shows the greatest risk.
Speculation from geologists has linked the seismicity to injections into the Arbuckle formation, a rock layer beneath the oil- and gas-producing layers in the region. Arbuckle rock is thought to be “under-pressured,” accepting water easily, but little is known about how the layer works. It’s possible that water being injected into the Arbuckle formation—which the Oklahoma Geological Survey says accounts for more than half of wastewater injection in the state—is finding its way into faults and causing movement.
Induced Seismicity
Wastewater injection is often linked with hydrofracturing, the form of natural gas extraction that has become common over the past decade, but the practice can be a part of other forms of oil and natural gas extraction as well.
Earlier this year, the USGS for the first time accounted for “induced seismicity”—that is, seismic activity believed to be brought on by human actions—in its reports. According to its first earthquake forecast depicting induced earthquakes, north-central Oklahoma shows the greatest risk.
Shuttered Wells, Decline in Quakes
In March, the Oklahoma Corporation Commission ordered hundreds of injections wells shut down to address the quake problem; injection was already on the downswing because lowering oil prices had led to slowing production in the state.
Last month, local media reported that Oklahoma was on pace to have fewer quakes in 2016 than it had in 2015—if so, it would be the first time since 2012 that the state registered a decline in seismic activity.