Race to stop US oil rig leak
New Orleans - Robotic submarines raced on Monday to stop oil from a sunken rig streaming into the Gulf of Mexico, as BP warned that sealing the seabed leaks could take three months if the operation fails.
The British energy giant, which leases the stricken Deepwater Horizon semi-submersible platform, is desperately trying to prevent a massive slick from growing and spreading to Louisiana's ecologically fragile coast.
Satellite images on Sunday showed the slick had spread by 50% in a day to cover an area of 1 550km², although officials said almost all the oil was just a thin veneer on the sea's surface.
BP has dispatched a flotilla of skimming vessels to mop up oil from the rig, which sank on Thursday while still ablaze, almost two days after a massive explosion that left 11 workers missing and presumed dead.
The crucial operations, though, are being conducted by four underwater vehicles almost a mile below on the seabed, where the riser that connects the wellhead to the rig is spewing out an estimated 42 000 gallons of oil a day.
Not been done before
"Those operations are ongoing. I know they have been working overnight but I don't know the progress that has been made," Bill Salvin, a spokesperson at the joint information centre set up to deal with the spill, told AFP.
Experts say that using the robotic vehicles to activate the blowout preventer - a giant 450-ton, 50-foot high machine near the wellhead that could effectively cap the well - is a long shot.
"It has not been done before, but we have the world's best experts working to make it happen," admitted BP executive Doug Suttles.
Richard Metcalf, a mechanical engineer at the pro-industry Mid-Continent Oil & Gas Association told AFP: "Essentially, they're trying to put a cork in a bottle of champagne."
Aware that the effort could well fail, BP is also preparing to drill relief wells that would permanently shut off the oil flow by injecting a special sealant into the wellhead - but this would take much longer.
"It is possible that it could take two to three months for a relief well to be drilled," said Salvin, adding that a "worst case scenario" could see them "lose total control of the well" and oil leaking at a much quicker rate.
'Very serious spill'
The spokesperson told AFP that it should be clear by Tuesday morning if the remotely-operated submarines would be able to activate the blowout preventer and stop the two leaks in the riser.
The US coast guard, which conducted two flights over the slick on Saturday and Sunday to assess the extent of the pollution, have described it as a "very serious spill".
Five aircraft and 32 spill response vessels - skimmers, tugs, barges and recovery boats - have been trying to mop up the slick but efforts were hampered over the weekend by winds and high seas.
So far, the slick is not threatening the coast of Louisiana where it could endanger ecologically fragile wetlands that are a paradise for rare waterfowl and other wildlife.
"In the trajectory analysis we don't see any impact to any shoreline within the next three days," Charlie Henry, scientific support co-ordinator of the US government's National Oceanic and Atmospheric Administration, told journalists on Sunday.
Environmentalists have sounded the alarm about the threat to Louisiana and experts say the spill has the potential to be the worst seen in the United States since the 1989 Exxon Valdez oil tanker disaster.
11 workers still missing
That spill, considered one of the worst-ever manmade disasters, poured nearly 11 million gallons of crude into Alaska's Prince William Sound, devastating some 750 miles of its once pristine shores.
Meanwhile, there was still no news of the 11 Deepwater Horizon crew missing since Tuesday's spectacular blast which shot balls of flame into the night sky.
The US coast guard aborted a massive air and sea search for the missing workers on Friday.
Investigations are ongoing into the cause of the accident.
BP officials have said they believe it was a blowout, caused when pressure control systems fail and oil shoots uncontrolled to the surface.