Disposal wells, and the large amounts of produced water they handle from oil and gas operations, are "very likely" the culprit for numerous earthquakes to strike Oklahoma, according to scientists with the Oklahoma Geological Survey (OGS).
Meanwhile, Oklahoma Gov. Mary Fallin's office unveiled a website to track earthquakes in the state, and to provide the public a new source for news and information about them.
In a two-page statement Tuesday, OGS interim director/state geologist Richard Andrews and state seismologist Austin Holland said historical data shows an average of one-and-a-half earthquakes of 3.0 magnitude or greater were recorded every year in Oklahoma.
But that rate has since increased to an average of about two earthquakes of 3.0 magnitude or greater for every week, on average, in 2013, and continued increasing in 2014, to a rate of about two-and-a-half earthquakes of 3.0 magnitude or greater every day. Those figures equate to a seismicity rate in 2013 that was 70 times greater than the background rate observed in 2008; the current rate is now about 600 times greater.
"Based on observed seismicity and geographical trends following major oil and gas plays with large amounts of produced water, the rates and trends in seismicity are very unlikely to represent a naturally occurring process," Andrews and Holland said. "The OGS considers it very likely that the majority of recent earthquakes, particularly those in central and north-central Oklahoma, are triggered by the injection of produced water in disposal wells."
The earthquakes were primarily occurring along faults both optimally and sub-optimally oriented within the tectonic stress regime in Oklahoma, said the duo. Most of the earthquakes were occurring within the crystalline basement, and the majority of injection wells were targeting the Arbuckle formation, which closely overlies the crystalline basement.
Andrews and Holland said the OGS was adding staff and updating its seismic equipment to improve seismic monitoring within the state. OGS also is compiling a database of known fault locations, which would include data voluntarily submitted by the Oklahoma Independent Petroleum Association (OIPA).
Separately Tuesday, the Oklahoma Corporation Commission (OCC) said it was "grateful" for the OGS's work, and was incorporating the findings into its response to triggered seismic events. Earlier this month, the OCC's Oil and Gas Conservation Division (OGCD) issued rules for injection wells targeting the Arbuckle Formation (see Shale Daily, April 2).
"There will no doubt be more steps to take, and all options available to the OCC are on the table," said OCC spokesman Matt Skinner. "There is no issue that has a higher priority for this agency, and the continuing work and commitment of OGS is central to this effort."
Fallin said the new "Earthquakes in Oklahoma" website would "help provide Oklahomans with up-to-date and timely information about our ongoing earthquake response...Oklahoma state agencies are already taking action to address this issue and protect homeowners."
Last fall, Oklahoma regulators shut in a disposal well that was thought to have been drilled too deep following a spate of seismic activity in the area (see Shale Daily, Oct. 31, 2014).