Timeline: Series of failures led to oil rig blast


Associated Press


The timeline described in the documents provides the most detailed account of what may have caused the April 20 blast that killed 11 workers and touched off the underwater gusher that has poured more than 3 million gallons of crude into the Gulf.

Portions of the interviews, two written and one taped, were read to an Associated Press reporter by Robert Bea, a University of California Berkeley engineering professor who serves on a National Academy of Engineering panel on oil pipeline safety and worked for BP PLC as a risk assessment consultant during the 1990s. He received them from industry friends seeking his expert opinion.

Seven BP executives were on board the Deepwater Horizon rig celebrating the project's safety record, according to the transcripts. Meanwhile, the rig was being converted from an exploration well to a production well.

As the workers removed pressure from the drilling column and introduced heat to set the cement seal around the wellhead, the chemical reaction created a gas bubble and the cement around the pipe destabilized, according to the interviews.

Deep beneath the seafloor, methane gas is in a slushy, crystalline form. As the bubble rose up the drill column from the high-pressure environs of the deep to the less pressurized shallows, it in-tensified and grew, breaking through the rig's various safety barriers, the interviews said.

Up on the rig, the first thing workers noticed was the seawater in the drill column suddenly shooting back out at them, rocketing 240 feet in the air. Then, the gas surfaced. Then the oil.

"The gas flooded into an adjoining room with exposed ignition sources, he said.


The executives were injured but survived. Nine rig crew on the rig floor and two engineers died, according to one account.

A BP-chartered vessel lowered a 100-ton concrete-and-steel vault onto a ruptured well in the Gulf of Mexico on Friday, an important step in a delicate and unprecedented attempt to stop most of the gushing crude fouling the sea.


"It appears to be going exactly as we hoped," BP spokesman Bill Salvin told The Associated Press on Friday afternoon, shortly after the four-story device hit the seafloor. "Still lots of challenges ahead, but this is very good progress."


So far about 3 million gallons have leaked in an environmental crisis that has been unfolding since a the deepwater drilling platform exploded .