WILLISTON, N.D. — An oil well that leaked an unknown amount of oil, gas and other liquids over the weekend has been plugged in northwestern North Dakota, state officials said Tuesday.
The well sprayed mist and emitted hydrogen sulfide, prompting air-quality monitoring and road closures in the area near Tioga after it was discovered Friday. The spill was contained to the well site, according to the well owner, which said it was still assessing how much liquid leaked.
Denver-based Emerald Oil Inc. reported the incident to state regulators Friday. North Dakota's Department of Mineral Resources issued a statement on the incident on Monday.
Emerald Oil CEO McAndrew Rudisill said a break in a pipe near the surface likely caused the problem during hydraulic fracturing operations. He said the well was "killed" on Monday and has since been plugged. Williams County Emergency Manager Mike Hallesy confirmed the leak was under control by Tuesday.
But some of the mist migrated off site. Levels of hydrogen sulfide - a potentially dangerous product of the natural gas that is usually burned off or captured at well sites - were down to 10 parts per million Tuesday morning, prior to the well being plugged, said Terry O'Clair, the state Health Department's air quality director. Hallesy had reported hydrogen sulfide levels at 20 parts per million a day earlier.
"We get concerned when it's more than 10 parts per million," O'Clair said, noting that levels of 100 parts per million can be deadly.
Residents of two farms near the well incident, including one that was only 1,200 feet away, were notified and advised to shelter in their homes, Hallesy said.
Rudisill said all spilled fluids were contained. He acknowledged that the volume of the spill was not yet known, but he said it was minimal.
Crews were cleaning up the site and replacing some of the topsoil that had been affected, he said. Once that work is completed, the well will be unplugged. Rudisill said he expects fracking operations at the well to resume later this week.
Hydraulic fracturing is the practice of injecting a pressurized mix of water, sand and chemicals into a drilled well in order to fracture rocks and promote the flow of oil and gas.
Alison Ritter, a public information officer with the Department of Mineral Resources, said the well is on confidential well status, which limits the amount of information her office can release to the public about the well for six months. The status is granted to entice exploration and protect oil companies from competitors.