The Oklahoma Geological Survey — which monitors seismic activity in the state — continues to acknowledged in a Feb. 17 position statement that “both fluid injection and withdrawal in the subsurface can trigger earthquakes,” but stopped short of blaming the oil and gas industry for increased temblors in recent years.
The vast majority of Oklahoma quakes happen within a few miles of injection wells, but the statement throws some cold water on a connection between the two.
About 80% of the State is within 15 kilometers (9 miles) of an Underground Injection Control (UIC) Class II water disposal or enhanced oil recovery injection well. For this reason, identifying possible induced or triggered seismicity requires more scientific evidence than simply identifying spatial correlations. It is also important to note that about 99% of the earthquakes that have occurred in Oklahoma over the past few years also lie within 9 miles of a UIC Class II well.
That doesn’t mean injection wells aren’t the cause of the earthquake uptick, just that there are too many injection wells to be sure, and more evidence is needed.
But while OGS gathers more evidence, many scientists have seen more than enough to convince them of a link, as StateImpact has reported.
University of Oklahoma seismologist Katie Keranen, who has studied a 5.6 earthquake that hit Oklahoma in November 2011, found the link between the “zone of injection” and the seismic activity “compelling.” There are three deep injection wells within two-and-a-half miles of that quake’s epicenter, according to Energy Wire.
And if you really want to wrap your head around how injections wells might cause earthquakes, check out StateImpact reporter Joe Wertz’ handy video on the issue.