This was the second attempt to drill a well in about the same spot. The first well had to be abandoned because the well had been drilled too fast (under pressure from BP to bring the well in quickly). Result: the rock fractured, causing loss of control of pressure in the well. Twenty-five million bucks down the drain, said BP to the crew. So they had to try again, in a rock formation known to be problematic.

Early on while drilling the second well (the one that eventually blew up) an accident damaged part of the blowout preventer (BOP). According to Williams, they were conducting a routine test of the annular, a ring of rubber that closes around the well at the top of the BOP stack. While the annular was closed, thus closing off the well, a driller accidentally pushed a joystick, which pulled the pipe casing up through the rubber seal at very high pressure. A short time later, after drilling had resumed, pieces of rubber began coming up from the bottom of the well. A drilling supervisor told Williams that the rubber debris was "no big deal".

The BOP has two redundant electronics boxes, called pods, which communicate with the surface. These are critical devices which trigger the BOP to close the well in emergency. One of the two pods was problematic and occasionally inoperable. The batteries on the BOP were also weak.

The well was in the process of being closed with cement plugs when the blowout occurred. The day of the blowout, there was a disagreement between the Transocean supervisor and the BP supervisor over how that should be accomplished. The Transocean guy wanted to keep mud in the well (i.e., keep pressure in the well) during the cementing. The BP guy wanted the mud pulled from the well for cementing, because it was faster and they were already behind schedule. The BP guy won the argument. If pressure had been maintained in the well during the cementing operation, the blowout would not have occurred.

The bottom line: the blowout was caused by gross negligence on the part of BP. There is no other way to spin it.

Here are embedded vids from the CBS site; they contain some stuff not aired, but leave out critical details that were aired, specifically an interview with an engineering professor Robert Bea from UC Berkeley. It was Bea who said that the blowout would not have occurred if mud had been maintained during the cementing process.

UPDATE 2:

See bottom two embeds for entire aired 60 minutes segment!

h/t to Grannyhelen in the comments for noting this.

UPDATE:

As OLinda noted in the comments, Bea also said that one of the other problems was that once the rubber annular was damaged, the pressure readings they were getting from the bottom of the well would be inaccurate.

UPDATE 3:

Per dharmafarmer's fine suggestion in the comments, here's CBS's feedback page if you'd like to give them props.

Oil Rig part 1





Oil Rig part 2



Oil Rig part 3



Oil Rig part 4



Oil Rig part 5



Oil Rig part 6



Update 2: Entire segment on blowout

Entire segment, part 1



