concrete plugs in well. Transocean wanted to keep the mud in the pipe till AFTER the last concrete plug was put in. BP over-ruled him..said go ahead and remove the mud before putting in last concrete plug. This meant there was nothing to hold back any pressure from gas in the formation they drilled into.
http://www.cbsnews.com/stories/2010/05/16/60minutes/main6490197_page4.shtml?tag=contentMain;contentBody
In finishing the well, the plan was to have a subcontractor, Halliburton, place three concrete plugs, like corks, in the column. The Transocean manager wanted to do this with the column full of heavy drilling fluid - what drillers call "mud" - to keep the pressure down below contained. But the BP manager wanted to begin to remove the "mud" before the last plug was set. That would reduce the pressure controlling the well before the plugs were finished. (emphasis my own_JW)
Asked why BP would do that, Bea told Pelley, "It expedites the subsequent steps."
"It's a matter of going faster," Pelley remarked.
"Faster, sure," Bea replied.
(more)
Also, the blow-out preventer was damaged a couple weeks before the accident. Pieces of a part called an "annualar" (a big damn gasket) came up the pipe. This was a clear sign of trouble. There were also other parts of the BOP which weren't working.
Here's the link to the start of the show. TApe and transcript:
http://www.cbsnews.com/stories/2010/05/16/60minutes/main6490197.shtml