With the flow of oil into the Gulf of Mexico stopped after nearly three months, a key piece of evidence in the Deepwater Horizon spill â€” the blowout preventer â€” was raised by salvage crews in September in a 30-hour operation marked by tight security and scrutiny from government and law enforcement officials.
The 53-foot-tall, 325-ton blowout preventer (BOP) â€” a series of valves, shears and rams housed in a tower on the sea floor â€” did not activate automatically as designed to seal the drill pipe and cut off the flow of crude when the oil rig exploded on April 20. Efforts by rig operator BP Plc. to activate the device electronically from a ship and manually with remotely operated vehicles (ROVs) also failed, resulting in the largest offshore oil spill in U.S. history.
While officials know the explosion was triggered by a bubble of methane gas that rose from the well and expanded up the drill line, they donâ€™t know what caused the BOP to fail to activate. Possibilities include a problem with the mechanics of the device, debris that might have been forced into it during the explosion, lack of maintenance or a combination of factors.
The degree of liability in the spill for BP and rig owner Transocean could be influenced by what investigators find.
With the flow of oil stopped by a temporary cap on July 15 and later reinforced by a â€œstatic killâ€ of injected cement, the focus of the spill response shifted toward recovering the BOP from the seabed 5,000 feet below the surface of the Gulf of Mexico.
On Sept. 3, crews aboard the 312-foot Q4000, an offshore drilling ship owned by Helix Energy Solutions Group of Houston, unbolted the device from the wellhead with ROVs and began raising it. On board the vessel were officials from the FBI and the U.S. Justice Department, which later took possession of the BOP as evidence in its criminal investigation.
Retired Coast Guard Adm. Thad Allen, national incident commander for the Deepwater Horizon Unified Command, described the salvage at a news conference on Sept. 4 while the device was still being raised.
|After being raised from the seabed of the Gulf of Mexico, the blowout preventer and its associated riser were taken by barge up the Mississippi River to a NASA facility in New Orleans, where they are being examined as evidence in the federal criminal investigation into the fatal accident at the BP well. (Photo courtesy U.S. Coast Guard)|
â€œThe latching device that was used to recover the blowout preventer is actually a drill string, and as the blowout preventer is brought up to the surface, they have to disconnect the pieces of the drill string â€” the pipe â€” and store it as they bring it up,â€ he said. â€œSo on the Q4000, what happens on deck up there is rather complicated.â€
Allen said the weight of the material being lifted â€” the blowout preventer and 5,000 feet of 6-inch pipe â€” was about 1 million pounds.
The operation was delayed with the BOP about 500 feet below the surface due to methane hydrate crystals that had formed inside it. The hydrates, which are combustible, form when methane gas mixes with water under high pressure and in cold temperatures. As the crystals melted closer to the surface of the Gulf, crews on Q4000 sped up the process by injecting the BOP with water and methanol.
On the evening of Sept. 4, the device was lifted aboard the drillship. The lower marine riser package on top of the BOP was removed and both parts were secured on deck. The BOP and riser were later transferred to a barge and taken to a NASA facility in New Orleans for analysis.
Cameron Wallace, spokesman for Helix Energy Solutions, said the recovery of the BOP was not an unusual operation for the company, aside from the fact that â€œit was done so very slowly under the watchful eye of so many government agencies.â€
â€œHelix has been intervening in live-well bores in deep water for more than 20 years, so it was a pretty straightforward operation for us,â€ he said. â€œThe delay with the hydrates was the only problem we really encountered.â€