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December 09, 2009 --- Vol. 15, No. 95December 2009

Pressure build up from internal ice plugs likely cause of Lisburne pipeline spill

In a situation analogous to the bursting of a frozen water pipe during the winter, it appears that pressure from expanding ice plugs inside the 18-inch pipeline that carries three-phase fluids from Lisburne drill pad L-3 to the Lisburne Production Center caused the oil spill discovered Nov. 29 at one of the pipeline’s vertical support members.

Following an x-ray survey of the damaged pipeline, to guard against any safety hazard from possible continuing over pressure in the line, responders have been able to start removing heavily contaminated snow around the spill site. And on Dec. 7 a visual inspection of the line revealed a 24-inch lengthwise rupture, with the rupture displaying characteristics consistent with pressure inside the line having ripped the line open.

It appears that expanding internal ice plugs on either side of the rupture point had built up the fluid pressure in the line, BP spokesman Steve Rinehart told Petroleum News Dec. 8.

“We had ice plugs on either side of this leak. There’s roughly 1,300 feet in between the ice plugs,” Rinehart said. “… Ice expands as it freezes and those ice plugs growing on each side would … have exerted significant pressure on that material between them.”

And on Dec. 5 the spill response unified command published an estimated spill volume of about 46,000 gallons, a volume determined using mapping and surveying techniques applied at the spill site. That preliminary estimate will be later superseded by a more accurate estimate based on volumes of material recovered from contaminated snow. Fluid is no longer leaking from the pipeline.

BP does not know what proportion of the spill material consisted of produced water rather than oil. However, the damaged pipeline typically carried a mix of 75 percent water and 25 percent oil, Rinehart said.

See story in Dec. 13 issue, available online at noon, Friday Dec. 11 at www.PetroleumNews.com

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