The ruptured well that pumped almost 5million barrels of oil into the Gulf of Mexico has been secured and no longer constitutes a threat, it has been confirmed.
A new valve known as a blowout preventer was placed over the well on Friday after crews replaced a damaged device.
The old 300-ton blowout preventer was raised to the surface of the Gulf of Mexico early yesterday.
This will now be examined by investigators looking into the causes of the disaster.
Investigators may now be able to answer the most elusive question since the Deepwater Horizon rig explosion unleashed the massive oil spill more than four months ago – why did failed to stop the oil?
A crewman guided a crane to hoist the 50ft blowout preventer from a mile beneath the sea to the surface. It took more than 29 hours for the device to reach the surface of the gulf.
FBI agents were among the 137 people aboard the Helix Q4000 vessel, waiting to escort the device back to a Nasa facility in Louisiana for analysis.
Crews had been delayed after ice-like crystals – called hydrates – formed on the blowout preventer. The device could not be hoisted safely from the water until the combustible hydrates melted, said Darin Hilton, the captain of the Helix Q4000.
The crystals caused BP problems in May, when hydrates formed on a 100-ton, four-storey dome the company tried to place over the leak to contain it.
The April 20 explosion aboard the Deepwater Horizon killed 11 workers and led to 206million gallons of oil spewing from BP’s well.
Investigators know the explosion was triggered by a bubble of methane gas that escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before igniting.
But they do not know exactly how or why the gas escaped or why the blowout preventer did not seal the well pipe at the sea bottom after the eruption as it was supposed to.
Documents emerged showing that a part of the device had a hydraulic leak that would have reduced its effectiveness and that a passive “deadman” trigger had a low, perhaps even dead, battery.
Steve Newman, president of rig owner Transocean, told politicians after the disaster that there was no evidence the device itself failed and suggested debris might have been forced into it by the surging gas.
There have also been claims that the blowout preventer did not undergo a rigorous recertification process in 2005 as required by US regulators.