More than 400 saltwater disposal wells covering 5,000 sq miles of central Oklahoma are part of an expanded earthquake response plan to deal with the state’s rise in earthquake activity. Disposal wells in the deep Arbuckle formation have been associated with induced seismicity.
The Oklahoma Corporation Commission released its latest plan Mar. 7 after a regional plan for northwestern Oklahoma was outlined in February. Together, the two plans cover more 600 disposal wells covering some 10,000 sq miles.
Oklahoma researchers recorded more than 900 earthquakes greater than 3.0-magnitude during 2015, up from 578 in that category during 2014. As of early March, more than 140 earthquakes greater than 3.0-magnitude have hit the state, including eight greater than 4.0-magnitude.
Drilling disposal wells through the Arkbuckle formation into the crystalline basement could increase the risk of triggered earthquakes, some researchers say, adding they will evaluate statistics for several months for signs that earthquake numbers are decreasing.
OCC is working with the Oklahoma Geological Survey and the US Geological Survey.
Tim Baker, director of OCC’s oil and gas conservation division, said the central Oklahoma plan, like the northwest one, will reduce the total volumes of wastewater by 40% below 2014 totals.
Compared with 2015 average injection volumes, Baker said the two regional plans mean a reduction of more than 300,000 b/d. The volume reductions will be phased in during 2 months with full compliance by May 28.
The central Oklahoma expansion followed several localized actions, including restrictions in the Cushing, Crescent, and Edmond areas.
Companies having the largest number of disposal wells in the central Oklahoma regional plan are Devon Energy Corp., 54; American Energy Woodford LLC, 22; Equal Energy US Inc., 17; and Range Production Co., 16.
OCC also said it was expanding a previously defined area of interest (AOI) that included more restrictions on disposal well operations in areas that have yet to experience earthquake activity. That expansion will bring another 118 Arbuckle disposal wells under an earthquake risk system.
Operators will have to prove disposal wells have not been drilled into the basement rock, and they will have to provide daily and weekly volume reporting.
“It also eliminates the possibility of administrative approval of new Arbuckle disposal well applications,” Bakers said. “The AOI expansion is a proactive move to get ahead of the earthquake activity.”
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