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Deepwater Horizon: has ‘top kill’ worked?

BP is continuing efforts to ‘top kill’ the leaking oil well in the Gulf of Mexico, which is now the source of the worst oil spill in US history.

“They have been able to stop the hydro-carbons from coming up the well bore,” said Admiral Thad Allen today (ABC News). “The real challenge is to put enough mud into the well to keep the pressure where they can put a cement plug over the top.”

Initial attempts at the ‘top kill’ – which involves pumping heaving mud down into the well in an attempt to block the flow of oil – were stopped after large amount the mud was seen streaming back out. Mud then began being pumped again (NY Times).

David Summers, a mining engineer at Missouri University of Science and Technology, says, “They haven’t been able to totally balance the pressure. The column of mud in there should be stable enough to stand there by itself. But they’re still having to apply a little bit of pressure to keep the column stable. That means they may not have got the mud all the way down the well yet.” (Guardian.)

Apparently, a second procedure called a ‘junk shot’ has also taken place. This involves pushing debris into the system of valves that failed to shut off the oil after the accident (WSJ).

Officials dealing with the disaster have also raised their estimates of how much oil is leaking into the Gulf. Using three different methodologies a USGS team now puts the leak rate at between 12,000 and 19,000 barrels day.

This is far higher than the initial 5,000 barrels a day number, which has been criticised by some experts as far too low and the new higher number makes the Deepwater Horizon accident the biggest oil spill in US history, with at least 450,000 barrels leaked.

The Exxon Valdez disaster involved 250,000 barrels leaking. The Deepwater Horizon spill is still some way off the Ixtoc oil well, which leaked well over three million barrels into the Gulf of Mexico at the tail end of the 1970s. It is also far less than the deliberate spilling of some 10 million barrels during the first Gulf War.

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