EL DORADO, Ark. -- The Arkansas Oil and Gas Commission on Wednesday voted to ban wells for the disposal of natural gas drilling fluids from a region where hundreds of earthquakes have struck, a move officials said was necessary to prevent a potential catastrophe.
Commissioners voted 6-0 to close a disposal well between Greenbrier and Enola in the Fayetteville Shale, an area rich in natural gas that stretches across the state. The commission also voted 7-0 to issue a moratorium on new disposal wells in a 1,150-square-mile segment of the shale in central Arkansas north of Conway, the Arkansas Democrat-Gazette reported.
Three other disposal wells in that area have already been closed by their operators.
The moratorium would not affect the drilling of natural gas wells, but it changes how fluids from the process are disposed.
Gas companies have tapped reserves of natural gas in the Fayetteville Shale by injecting water and chemicals under high pressure to fracture the shale, a process known as fracking. The fluids that emerge in the process have the potential to taint rivers and drinking water.
Separate disposal wells are used by drillers to dump the fluids.
With a moratorium, companies would have to truck the fluids to injection wells elsewhere in Arkansas or in Oklahoma or Texas, Commission Deputy Director Shane Khoury told The Associated Press after Wednesday's vote. About 730 disposal wells are active in the state, he said.
The commission pinpointed four wells in central Arkansas that it said needed to be closed to prevent earthquakes. Those wells are near a fault system that has spawned dozens of earthquakes this year. A magnitude-4.7 earthquake in February near Greenbrier was the most powerful to hit the state in 35 years.
After two of the four stopped operating in March, there was a sharp decline in the number of earthquakes. In the 18 days before the shutdown, there were 85 quakes with a magnitude 2.5 or greater, but there were only 20 in the 18 days following the shutdown, according to the state Geological Survey.
The fault system was discovered after the state allowed operators to drill the four wells, Khoury said.
"Bottom line is had we known that the fault system existed ... we would never have permitted the well in the first place," Khoury said.
The last well still operating belonged to Deep-Six Water Disposal Services, a subsidiary of Oklahoma City-based Hurst Oil Investments Inc. Deep-Six contended its well did not have an effect on seismic activity nearby.
A company representative declined comment Wednesday. But an expert who testified at the commission's hearing said tiny earthquakes near the well did not have a proven link to the well, the Democrat-Gazette reported.
Haydar al-Shukri, director of the Arkansas Earthquake Center at the University of Arkansas-Little Rock, testified Wednesday that his testing recorded nearly 10,000 small seismic events near the Deep-Six well. Most were too small for humans to notice.
Only 280 of those seismic events happened within three miles of the well, a sign that the well wasn't the cause of most of them, al-Shukri said.
But Commissioner Mike Davis said the commission had to act to close the well after hearing two days of testimony.
"Our first and foremost obligation is to the safety of the citizens of the state of Arkansas," Davis said, according to the Democrat-Gazette.
Commission director Lawrence Bengal said the Deep-Six well was within the "geologic fabric" of the region and could contribute to earthquakes near Guy and Greenbrier even if the well was several miles from the fault.
Khoury told the AP the well would likely close within three to five business days.