Oil spill latest: Why 'Top Kill' failed

Last week, BP were optimistic that the 'Top Kill' method of flooding the blowout preventer (BOP) with mud and a binding agent and closing the well with concrete had a 65 percent chance of success, and despite promising early results stemming the flow of crude, BP have conceded that the method has failed.

The news is depressing, not least because of the continual devastation to the fragile wetlands, wildlife but to those making a living on the Gulf of Mexico coast. During a stop-in at affected coastal areas, President Barack Obama said the US would "do whatever it takes" to stem the flow and clean up the mess, including sending additional manpower to lay booms, clean beaches and help stricken wildlife.

Mr Obama explained that BP would be held responsible for the spiralling cost of the crisis (so far estimated at $930 million) but shouldered responsibly, saying "I'm the President and the buck stops with me."

"I give the people of this community and the entire gulf my word that we're going to hold ourselves accountable to do whatever it takes for as long as it takes to stop this catastrophe, to defend our natural resources, to repair the damage and to keep this region on its feet."

Why 'Top Kill' failed - Cement

BP are not sure why oil and gas is still leaking into the Gulf of Mexico, but think the flow of oil is getting through the cement wall at the base of the well and travelling up through the annulus between the production casing and the outer lining of the well. According to the Oil Drum, there is a chance that the oil broke through the cement wall, and is rising up along the production casing, in which it is also rising through the drill pipe once the oil reaches its lower end. Another possibility for oil reaching the bottom of the drill pipe could be that it is rising up the annulus, then flowing down the production casing, and eventually flowing back into the BOP via the annulus again.

Sealing the blowout preventer

The blowout preventer was invented so that, during drilling and exploration, the dramatic fountain of oil spray effect would be avoided, essentially protecting the crew at the surface and stopping the flow of oil. Because the flow of oil is normally up the outside of the drill pipe, the initial BOP design featured rams that pushed seals across the flow path through the BOP, and sealed against the side of the drill pipe. The issue with BP's well in the Gulf is that it is deep underwater, which means instead of the standard two seals - one to seal the production casing, and one to seal the drill pipe - the casing is tied to the Wellhead Collet Connector, which means the only tube running through the BOP will be the drill pipe.

The problem then, is that the pipe that runs through the two seals is open at the foot of the well, allowing oil to flow unchecked. The only way to seal the well allowing for the open pipe would be to mount a top ram set that has a set of shear cutting blades on it, that will cut through the pipe and seal the full face of the well. The pipes should shear, except it appears they didn't, which means the two shear blades didn't cross each other, and oil is still getting through.

The idea of the the junk shot would have been to block small gaps in the bottom of the BOP, which would occur by blasting small particles down the drill pipe, which would have plugged the small cracks between the shear blades, and in theory, prevent the oil from entering the sea.

However the depth of the well has prevented this from working; it is just too difficult to pump sealing particles and mud 3,367 feet down a drill pipe.

So it's another head-scratcher for Tony Heyward and BP, who along with top scientists sent from the US government need to come up with another plan to block the gushing well. If they cannot, then BP has hinted that it may be time to deploy another dome, and hope for more success than last time.

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Oil spill latest: The cost of clumsiness | Gulf oil spill latest: Containing the spill | Oil spill latest: BP still the company to clean up mess | US oil rig sinks and causes oil spill off US coast | Oil spill latest: A time to 'Top Kill' | Oil spill latest: update, top kill results | GDS Publishing | Oil spill latest: oil leaking at catastrophic levels | Oil spill latest: BP make strides to contain the spill

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