BISMARCK, N.D. (AP) — Crews successfully plugged an oil well blowout Tuesday in western North Dakota that had been spewing a mixture of oil and saltwater since the weekend, state and company officials said.
The oil well near White Earth, owned by Houston-based Oasis Petroleum North America LLC, had been out of control since late Saturday night and was capped at midmorning Tuesday, said Bill Suess, who heads oil spill investigations for the state Health Department.
Crews pumped into the well a slurry of bentonite clay and water, a concoction known as a "kill pill," to get the well under control.
"That mud and water that was pumped into it, killed it," Suess said. "Now that it's killed, we can start doing a better assessment."
Oasis Petroleum spokesman Brian Grove said the cause of the spill was still under investigation. The company said in a statement that "a leak on a surface pipe was the likely point of failure."
The well, which had been operating for four years, is located about 850 feet from the White Earth River, or about the length of three football fields. Seuss said a light sheen was seen on the river Sunday and crews placed 49 absorbent booms on the river to keep it from migrating four miles downstream and into Lake Sakakawea, the largest of the six reservoirs on the Missouri River.
"No sheen could be seen on the river on Monday," Suess said.
Suess said crews had recovered about 483,000 gallons of crude oil and saltwater — a byproduct of oil production — from the well site as of Tuesday morning. The recovered liquids were about evenly split between briny water and oil, he said.
A total estimate on the amount spilled has not been calculated, but Suess said it appeared most had been recovered.
Oasis said "the release has been contained to the well location itself, with the exception of some airborne mist." The company said tests show "no saltwater-related impacts to the White Earth River."
North Dakota regulators suspect the breach have been caused by from hydraulic fracturing operations at nearby well that was being drilled by the company.
Hydraulic fracturing, or fracking, is a process that uses pressurized water, chemicals and grit to break open oil and gasbearing rock up to two miles underground. The technique is credited with allowing the development of the rich Bakken shale and Three Forks formations in western North Dakota.
Suess and North Dakota Department of Mineral Resources spokeswoman Allison Ritter said the blowout had the characteristics of what drillers call a "frack hit" or "downhole communication" between wells because oil and saltwater spewed downward at the well instead of vertically. Such incidents are unusual in North Dakota, Ritter said.
"Communication" between wells happens when fractures of separate wells intersect. North Dakota does not allow well bores to be within 1,300 feet from each other to guard against it, Ritter said.
"It causes a ripple effect of pressure," Ritter said of a frack hit. "Pressure from one well is seen in another. We have previsions in place to prevent that from happening and we're trying to find out if that's what went wrong here."