Drilling mud, brine and diesel fuel spilled Monday onto a gravel pad and into a pit no longer used at the Kuparuk oil field operated by ConocoPhillips on Alaska's North Slope, according to the Department of Environmental Conservation.
The spill happened when a gasket on a steel pipe -- what the industry calls a "hard line" -- failed. Water-based drilling fluids were being sent through the pipe from a processing facility to a disposal well, according to ConocoPhillips.
Cleanup began Monday and was continuing Tuesday for a spill initially estimated at 85 barrels, or 3,570 gallons, according to DEC and ConocoPhillips. The volume will probably end up less than that, said Natalie Lowman, spokeswoman for ConocoPhillips.
"Any spill we take seriously, and this is no exception," Lowman said. "The cleanup effort is very, very rigorous."
No one was hurt, and oil production is not affected, she said. The leak was stopped immediately, she said. The pipe is routinely inspected while in use. ConocoPhillips has contracted with Alaska Clean Seas for the cleanup.
An area of 3,000 to 4,000 square feet was contaminated, according to DEC.
The ball mill facility processing the drilling waste was shut down and the steel pipe was isolated to stop the spill, according to a DEC report. The failed gasket section was repaired and the line was inspected to make sure nothing else was leaking, the situation report said.
Besides drilling mud, the spilled materials included salt water used to clean out pipes and diesel fuel used to prevent freezing in the line, according to DEC.
Winter cleanups usually go quickly because equipment can be moved in over the frozen tundra, said Ashley Adamczak, a Fairbanks-based environmental program specialist with DEC.
"Things freeze in place," she said. "It's not spreading any more."
The reserve pit was an old receptacle for drilling waste that had been cleaned up and closed. But now it's contaminated again and must be cleaned up, Adamczak said.
Crews are building a snow ramp from the gravel pad into the reserve pit so that workers can get into the area. The ice in the pit is not thick enough to support heavy equipment, so crews are using smaller machines designed to rip up frozen, contaminated gravel, Adamczak said.
Three spill technicians are using Bobcats to work the cleanup and already have removed 60 cubic yards of material from the gravel pad, Lowman said early Tuesday afternoon.
A loader was recovering the contaminated material and taking it to a waste storage area for later disposal, the DEC report said.
Oil companies operating in Alaska have programs in place that are intended to replace equipment before it fails, but problems can still occur, Adamczak said.
"It's just like with your car. You can take it in for regular inspections, but sometimes in between, something will happen," she said.
ConocoPhillips is investigating why the O-ring gasket failed, Lowman said.