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HOUSTON (Reuters) - Oklahoma's oil and gas regulator on Friday issued a wider directive limiting future increases in wastewater disposal underground in another effort to address a rash of temblors that have occurred amid the shale boom.
The guidelines include wells in Oklahoma's Arbuckle formation that previously were required to restrict disposal volumes and some potentially high-volume wells not previously covered.
Those wells were not part of earlier orders because there had not been reports of seismic activity in their area.
In total, the directive will cover 654 wastewater disposal wells in the Arbuckle formation, the vast majority of which have already had volume restrictions, the Oklahoma Corporation Commission (OCC) said on Friday.
There are 71 wells included that were not under prior directives, OCC spokesman Matt Skinner said in a telephone interview.
Oklahoma has experienced a sharp rise in earthquakes in the past few years due to injection of saltwater, a normal byproduct of oil and gas drilling activities, into deep disposal wells. The state has been recording 2.5 earthquakes daily of magnitude 3.0 or greater, a rate 600 times higher than before 2008, according to the Oklahoma Geological Survey.
The Arbuckle is popular for wastewater disposal because it is the state's deepest formation and can handle vast amounts of water with little pressure.
Operators have 30 days to make adjustments to comply with the new guidelines. They can dispose wastewater in formations outside of the Arbuckle.
Directives issued by the state to curb wastewater disposal have yielded positive results, the OCC said on Friday. So far this year, Oklahoma has experienced an average of 1.38 earthquakes per day of magnitude 2.7 or higher, compared with 5.39 per day in 2015 and 3.61 per day in 2016.
But a rise in oil prices to above $50 per barrel this year has given hope to U.S. shale oil firms that production activity will increase.
Some wells in the Arbuckle could add more than 2 million barrels of wastewater without the directive, the OCC said.
"Right now the data indicates we need to look ahead and prevent this from happening," Skinner said on Friday.
A pair of large quakes last year near the massive oil storage hub in Cushing, Oklahoma, further stoked concerns among residents about the safety of its tanks and pipelines, which hold over 60 million barrels of oil.
Reporting by Liz Hampton; Editing by Leslie Adler