Crews had been delayed raising the device after ice-like crystals, called hydrates, formed on it. The device couldn’t be safely lifted from the water until the hydrates melted because they are combustible, said Darin Hilton, the captain of the Helix Q4000.
Hydrates form when gases such as methane mix with water under high pressure and cold temperatures. The crystals caused BP problems in May, when hydrates formed on a 100-ton, 4-story 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 an estimated 206 million gallons of oil spewing from BP’s undersea 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 don’t know exactly how or why the gas escaped. And they don’t know why the blowout preventer didn’t seal the well pipe at the sea bottom after the eruption, as it was supposed to. While the device didn’t close — or may have closed partly — investigative hearings have produced no clear picture of why it didn’t plug the well.
Documents emerged showing that a part of the device had a hydraulic leak, which 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 lawmakers following 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 has also been testimony that the device didn’t undergo a rigorous recertification process in 2005 as required by federal regulators.
Testimony from BP and Transocean officials also showed that repairs were not always authorized by the manufacturer, Cameron International, and that confusion about the equipment delayed attempts to close the well in the days after the explosion.
