Underwater work to halt the North Sea’s worst oil leak in a decade began last night after the ruptured pipe – which still contains hundreds of tonnes of oil – began floating off the seabed.
Shell has laid blankets of concrete on top of the broken flowline at Gannet Alpha amid fears more light crude could spill into the sea.
About 218 tonnes of oil, equal to 1,300 barrels, has already escaped and Shell is now fighting to keep another 600 tonnes inside the subsea structure, 113 miles east of Aberdeen.
The initial leak was brought under control earlier this week but oil is now escaping from a nearby release valve, which is proving difficult to get to.
Yesterday, Hugh Shaw, the UK Government’s representative for maritime salvage and intervention, revealed that, since the pressure was taken out of the pipe, an area of it has started floating.
“We have a situation where approximately 1km (two-thirds of a mile) of the pipeline has raised, with some internal buoyancy. It’s approximately a metre-and-a half (5ft) above the seabed,” he said. “I’m very conscious that we try and keep that pipeline in its current position until we know it’s safe to try and remove any hydrocarbons from the line.”
Shell hopes to get a diver into the sea today to shut the valve.
He added: “Our intention will be to try and close these valves on Friday. We will do it during daylight hours and that will enable us to have government surveillance aircraft on scene and monitoring the situation.”
Around 10 concrete weights, known as rock mattresses, were positioned yesterday to secure the flowline to the seabed, so it does not move or create further problems.
In a statement, Shell said it was continuing to make “good progress” towards stopping the leak.
Around one barrel of oil a day is currently escaping.
Yesterday – after it emerged that the first oiled bird had been discovered in the area affected by the spill – RSPB Scotland called for Shell to release its most recent pipeline inspection report.
A spokesman said: “We would like Shell to publish details of the last recent pipeline inspection report. That would be very helpful because they have been talking about subsea infrastructure. Some of that now may be quite old and now would be a good time to let the public know about the situation.”
The Department of Energy and Climate Change will be investigating the incident.
Meanwhile, fellow oil major BP says it is investigating a new sheen in the Gulf of Mexico but there is no immediate indication it is the result of a new oil spill.
A catastrophic explosion in April 2010 at BP’s Macondo well in the Gulf killed 11 men and led to the worst offshore oil spill in US history. BP did not make clear what the source of the new sheen was yesterday, but said it was not found near “any existing BP operations”.
The company said in a statement the sheen was found near two abandoned exploration well sites and it had sent a “remote-operated vehicle” to examine the underwater wells.
Spokeswoman Sheila Williams said “there is a lot of sheen in the Gulf of Mexico area” and that the substance did not necessarily come from a BP site.