The latest in a series of leaks from Cook Inlet oil and gas pipelines led Unocal to stop production Thursday from its King Salmon Platform.
The King Salmon Platform had been producing about 9,000 barrels of crude oil and 3.6 million cubic feet of natural gas per day before it was shut in, said Unocal spokesperson Roxanne Sinz. All of the gas was used as fuel on the platform.
According to the Alaska Department of Environmental Conservation, workers had seen droplets of oil floating near the platform for about two weeks. Originally, they believed the source was on the platform. On Wednes-day, though, they concluded the source actually was underwater.
Thursday at about 5 p.m., Unocal shut in the platform and flushed the eight-inch diameter pipeline that carries crude oil from it to Trading Bay with sea water. Workers planned to send a piece of equipment called a pig through the line to clean it, flush it again with sea water, then pressure test it with water to check for leaks.
If no leaks are detected in the oil line, workers will check an eight-inch pipeline that brings gas used as fuel on the platform from Trading Bay.
The King Salmon Platform was installed in 1967. The undersea oil pipeline was pressure tested last February as a precaution following a spill from a subsea pipeline serving the Dolly Varden Platform. February tests on the King Salmon pipeline found no anomalies.
According to DEC, oil appears to be bubbling intermittently from a subsea source adjacent to the platform. On Thursday, beginning at about 10:20 a.m., droplets floated to the surface for about 50 minutes, producing a sheen 20-feet wide and 400-yards long.
Another sheen appeared about 9:30 a.m. Friday. According to DEC, the sheen has dissipated too quickly for any oil to be recovered. The amount spilled is unknown. There has been no oiled wildlife observed. Water around the platform is about 73-feet deep.
Leslie Pearson, DEC on-scene coordinator, said the oil seems to appear at slack low tide, then disappears when the tide shifts.
The oil could be coming from a leak in the vertical pipe that runs through a platform leg to connect with the line on the sea floor, she said. The vertical pipes can suffer corrosion if they are subjected to tidal action within the legs, and piping within the legs is difficult to inspect.
Pearson said Cook Inlet Spill Prevention and Response Inc. plans to send a ship to take samples from the sheen. Those could help to identify its source. If there is a leak in the vertical pipe, Unocal will have to devise a strategy to fix it, Pearson said.
Meanwhile, a crude oil pipeline Amoco abandoned about 1984 appears to be the source of an unrelated sheen first observed July 31 near Unocal's Baker Platform, Pearson said. Samples from the sheen appear to match samples of oil fluid drawn from the abandoned pipeline.
Sinz said the sheen near Baker Platform has not reappeared since Aug. 11, when a vacuum was applied to the Nikiski end of the abandoned pipeline.
BP, which bought Amoco, has been working with Unocal to investigate the sheen and find a fix, but Unocal, which is better equipped to work in Cook Inlet, has taken the lead. Unocal conducted a side-scan sonar survey Aug. 11 to determine the condition of the abandoned pipeline. Pearson said BP is awaiting side-scan sonar results so it can come up with a plan for cleaning the line.
"The key is to find what condition that line is in. Can it be flushed? Are other options to clean it better? Can they put a pig through it?" she said.
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