Based on new geological data, state and federal officials lowered by 22 the number injection wells ordered to be shut in an area of Oklahoma near the city of Pawnee, where a 5.8-magnitude earthquake occurred September 3.
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Monday's action was a collaborative effort involving the Oklahoma Corporation Commission's Oil and Gas Division and the US Environmental Protection Agency, as it involves Osage County, where the injection wells are under EPA jurisdiction. The wells to be closed include 27 under OCC jurisdiction and five under EPA jurisdiction.
State officials said the 27 wastewater wells ordered to be shut compared with the shutdown of 37 wastewater injection wells that OCC the announced within hours of the quake earlier this month. Meanwhile, the EPA ordered the shut-in of five wells in its area of jurisdiction, down from 17 shut-ins the agency announced earlier this month.
At the same time the OCC expanded the area of concern from a 725-square-mile area around the city of Pawnee to a 1,116-square-mile area.
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The mandatory shut-ins are expected to last at least six months and may become permanent, depending on new data that is collected, officials said.
The OCC action follows and clarifies an emergency action the commission's OGD announced the day of the quake, the largest in state history.
Monday's order will result in the shutting in of 40,000 b/d of wastewater injections in the wells within the oil and gas division's jurisdiction, according to an OCC statement.
There are 67 injection wells that dispose into the deep Arbuckle formation in the geological area of interest where the officials are considering taking action, 48 within OCC's jurisdiction and 19 within EPA's jurisdiction.
In a conference call with reporters, Jerry Boak, director of Oklahoma Geological Survey, said state officials moved revised shut-in plans for the wells within the OCC jurisdiction based on continued study of the area that the OGS had conducted in the wake of the September 3 quake.
In addition to scaling back on the number of injection wells affected by the September 3 shut-in order, "the emphasis has been changed," OGD Director Tim Baker said.
Given the new OGS data on the direction in which the fault lines in the area run, rather than focusing on injection wells that lie along a line from the northeast to southwest of the quake's center, the OGD order focused on wells in a line that runs in more of an east-west direction, he said.
Based on the OCC's decision to expand the seismicity impact area of concern, "EPA has contacted three additional injection well operators in the Osage Nation Minerals Estate and requested them to reduce their disposal levels by 25% based on a recent 30-day average of actual disposal volumes," EPA spokesman David Gray said in an email Monday.
Gray said the agency "has also contacted the original 17 well operators to discuss next steps. Eleven can resume operations at a 25% reduction in disposal levels -- for a total of 14 wells operating at reduced volumes."
One well was confirmed to be outside the EPA's area of concern, he said.
"Five wells in the Osage Nation Minerals Estate have been requested to remain shut-in," Gray said.
He said the EPA expects to make additional decisions as to the possible shutting in of injection wells in the area of as the US Geological Survey "continues to evaluate seismic activities in the area and provide information to regulatory officials."
The issue of seismic activity induced by injection wells has become an increasingly important issue in Oklahoma, which has surpassed California as being the most seismically active state in the US.
--Jim Magill, email@example.com
--Edited by Jason Lindquist, firstname.lastname@example.org