Well I figure I should weigh in on this one seeings how I have been in the oil industry for over 20 years.
The failure was caused by several factors:
Thermal cement job by Halliburton that went bad. Why? Who knows. But the density of the cement could have been bad or it could have just been bad cement. A thermal cement is set off by friction and heat and it will flash. They say it washed out causing a gas kick.
Substandard blowout preventer. Americans are not required to follow the same standards as Canada or the UK for offshore BOP's. A BOP is comprised of not one, but several failsafes. First you have a pipe ram which closes in around the pipe if there is pipe in the well. Failure 1.
Then you have the blind ram which will close no matter what. Failure 2.
Then you have a shear ram, which is like the holy fuck button, it will cut the pipe off and shut the well in. Failure 3.
When the rig sank it broke off the casing from the well and basically twisted the and pipe. For the record it's not impossible to stab an overshot pipe onto a stick up, the overshot has a set of slips, when it's lowered over the pipe and then pulled up, the slips lock on and seal the well. Because it's such a clusterfuck down there, it's a lost cause trying that.
The kill method is a great method for killing a well, basically you hammer the well with a heavyweight blended barite based mud, and pump the shit out of it until the well dies. Once again because it's such a clusterfuck down there they pumped it so hard that they further split the casing, although BP's not saying anything, I can guarantee you that's what happened.
Despitte all the lies and bullshit you hear, and all the feeble attempts they are making, please don't kid yourselves, none of what they are doing is going to help much, it's just being done to appease the people who know fuck all about what's really happening, basically anyone in the world who has never worked on an oil rig or know anything about oil wells.
The only actual sollution is to drill a relief well not only into the same formation but to intersect the spewing well, and I know some of you might be thinking "bullshit there's no way they can be that accurate", but they can hit that well within mm without a problem, and then they can cement off the bad well. The problem with that is it will take a minimum of 3 months to do that.
This is going to be the largest man made polluting disaster the world has ever seen.