OKLAHOMA – Because of the rate of earthquakes recorded in Oklahoma has increased “remarkably” in less than a year, the U.S. Geological Survey warned – three months ago – that the chances of a “damaging” temblor in Central Oklahoma have increased “significantly.”
Further, the federal agency reported that a statistical analysis indicates oilfield wastewater injected into deep geological formations is “a likely contributing factor” to the increased number of quakes.
“I don’t know how long this has to continue, how severe it has to get, and how many scientific studies have to be undertaken, before Oklahomans collectively accept that there is hard evidence that these earthquakes are not naturally occurring phenomena,” state Sen. Jerry Ellis said Tuesday.
The Oklahoma Geological Survey counted 2,966 tremors in Oklahoma during the first seven months of this year, research seismologist Amberlee Darold reported. Of those events, 910, or 30% of them, registered at or greater than magnitude 2.5, she said. The two largest were magnitude 4.5; one occurred in Logan County, near Marshall, the other in Oklahoma County, near Luther.
From Jan. 1 through July 31 the USGS recorded seismic activity at numerous other locations in the state. Tremors were logged in or near Guthrie, Edmond, Spencer, Medford, Choctaw, Jones, Harrah, Pawnee, Yale, Stillwater, Perkins, Enid, Perry, Cherokee, Tonkawa, Coalgate, Wetumka, Prague, Hartshorne, McAlester, Boley, Chandler, Stroud, El Reno, Langston, Crescent, and McCord southeast of Ponca City in far western Osage County.
Several other locations in the state have been shaken in the not-too-distant past, Ellis, D-Valliant, pointed out.
The federal agency reported that the rate of earthquakes in the Sooner State logged since October 2013 had increased about 50%, “significantly increasing the chance for damaging magnitude 5.5 or greater quake” in central Oklahoma.
Furthermore, the USGS reported conducting a statistical analysis of the “recent earthquake rate changes” and determined that “they do not seem to be due to typical, random fluctuations in natural seismicity rates.”
The analysis posits that “a likely contributing factor to the increase in earthquakes is triggering by wastewater injected into deep geologic formations,” the USGS reported. OGS studies “also indicate that some of the earthquakes in Oklahoma are due to fluid injection,” the USGS added.
Approximately 12,000 injection wells have been drilled in this state, records of the Oklahoma Corporation Commission reflect. The majority of those are wells used in enhanced recovery, which seismologists do not consider to be a potential source of earthquakes.
But at least 3,356 of the wells are disposal wells which accepted nearly 1.09 billion barrels of wastewater – 45.7 billion gallons – from oil and gas production operations in 2012. The five largest of those wells, in terms of volumes of wastewater accepted, are all located in Oklahoma County, east of Interstate 35 between I-40 and I-240.
The total volume of saltwater disposed of in Oklahoma has been rising steadily: from 844 million barrels in 2007 to more than 939 million barrels (39.45 billion gallons) in 2011, Corporation Commission ledgers show.
Jackman said 22 disposal wells in the Oklahoma City – Shawnee – Jones – Edmond earthquake swarm area receive an average of 20 million tons, 96 million gallons, of saltwater and oilfield wastewater annually. Similarly, a dozen disposal wells in the Enid – Pond Creek – Jefferson area accept an average of 6.8 million tons, 50 million gallons, of oilfield wastewater each year, Jackman said.