The trans-Alaska pipeline was shut down just after midnight Friday so crews could begin installing a bypass around a leaky line at Pump Station 1, according to Alyeska Pipeline Service Co., which runs the 800-mile pipeline.
North Slope oil is not expected to flow for 36 hours while the 157-foot section of pipe is put into place, Alyeska said in a press release.
Leaking oil discovered during a morning inspection Jan. 8 led to a four-day shutdown, the second longest in the pipeline's history. It is uncertain if oil escaped a concrete housing around the line, but none has been discovered outside, Alyeska said.
Production from the more than two dozen North Slope oil fields run by BP and Conoco Phillips ramped down to 5 percent of normal for those four days at Alyeska's request. About $200 million in oil that otherwise would have been produced stayed in the ground over those four days.
An interim restart Tuesday allowed Alyeska to drain two storage tanks of a combined 420,000 barrels of oil, said Alyeska spokeswoman Michelle Egan.
The Prudhoe Bay producers are able to keep operating during the new shutdown, to a certain extent, by pumping oil into those tanks, but the overall level of production Saturday was unclear, Egan said.
Alyeska is watching those storage tanks closely as producers continue to send oil to them, Egan said.
"We're balancing with them on the amount of oil in those tanks," she said. "It's a balancing act."
Plans to start work Saturday morning on the bypass line were tentative because a weather hold at Fairbanks International Airport had slowed the shipment of some parts. But those parts arrived and the shutdown went ahead, Egan said.
Forecasters expected temperatures to drop Saturday night, with a low around 15 below, according to the National Weather Service.
Cold weather could be a concern for Alyeska, BP and Conoco, whose crews must work to keep lines and other infrastructure warm and operational.
As they worked in shifts to get the new line in place, Alyeska personnel wore heavy Arctic gear to stay warm, Egan said. Extra heaters are set up in surrounding buildings so the men and women can warm up, and shelters at the job site also kept them warm, she said.
"In some of the areas where they're working outside, where it's safe, we have sort of a little tent made out of visquine with some heat piped into it to keep them out of the wind and the elements," Egan said.
Alyeska will be monitoring temperatures at different points along the 800-mile pipeline, Egan said. Oil moves through the pipeline easier as friction heats its passage through the pipe.
The concern is that "resident oil" will build up with the cold and make restarting the pipeline more difficult, Egan said.
Crews also will be taking care to keep the pump stations warm and oil recirculating through the lines there, Egan said.
A restart of the pipeline slated for noon Sunday could come earlier or later, Egan said, but Alyeska is still looking at staying within that 36-hour shutdown window.
Alyeska runs the pipeline and Valdez tanker port for the five companies that own them: BP, Conoco, Exxon Mobil, Koch Industries and Chevron. The pipeline carries all of the North Slope oil production -- just over 10 percent of U.S. production.
By CASEY GROVE
casey.grove@adn.com