Feb 14 (Reuters) - A Whiting Petroleum Corp oil well in North Dakota was leaking drilling fluids after a blowout late on Thursday, company and state officials said on Friday.
The well lost control after a blowout preventer failed and was leaking between 50 and 70 barrels per day of fracking fluid that contains chemicals, water and sand, a company spokesman said.
The leak, close to the frozen Cherry Creek in McKenzie County, was contained and the fluids were being collected and trucked from the site. No liquids entered the water, Whiting said.
Fracking fluid is pumped into a well under pressure to fracture rock deep underground to release oil or natural gas.
A blowout typically occurs when an unexpected burst of high pressure comes up the well, causing a loss of control.
"The well is not under control," said Kris Roberts, a spokesman for the North Dakota Department of Health on Friday afternoon. "They're still diverting what's flowing from the well into storage tanks and hauling that."
A three-foot berm has been placed around the well, containing the liquids within the site, Lynn Helms, the head of North Dakota's Department of Mineral Resources, said on a conference call.
Some "mist," a combination of oil and water, did spray onto the frozen creek, but because of the ice and the snow it will be easier to clean up, Helms said.
"This a large (blowout) and also in terms of health and human risk it's a big one. Pressure and control of a well is essentially priority number one for oil and gas companies," Helms said, referring to the risk to personnel working on site.
He said there would be a "very serious postmortem" conducted with the company.
North Dakota is home to the giant Bakken shale oil formation and has experienced a boom in oil production especially in the counties of McKenzie, Williams, Dunn and Mountrail in the west of the state.