It may have been reported as the primary cause, but the blowout preventer is supposed to the be mechanism of last report to smother a blowout. The primary cause was a gas pocket blowout which exploded. Before cementing a well like that, a series of light and heavy fluids (lighter and heavier than both sea water and oil, depending) are pumped into the well to clear out pockets of gas and oil, and then to plug the well in preparation for cementing. After each time fluids are pumped, pressure tests are performed to find out whether more of the same should be pumped in, or if a different weight of fluids are needed. As things progress, heavier fluid (which amounts to a thick mud) goes in to bolster the well. Once all is OK and the heavy fluid has capped he well, lighter fluid and sea water is pumped into the pipes to clear the way for the final cementing. If there is any leak when the heavy fluid is pumped out, and lighter fluid is pumped in, the well cap is severely weakened. If there is a high pressure gas pocket down there, the cap blows and you have a blowout.
Here's the thing... records show that three tests were performed, but real-time recorded data preserved back on-shore ends at 3PM (the well blew at 10PM). Tests are recorded at the rig and are then transmitted to shore. But the data isn't transmitted in real-time, as several hours can pass before the data gets mirrored on shore. So, basically, the final seven hours of data, and all written logs, went down in the explosion.
The final test of the three, performed just before 3PM, showed there was still some gas leaking at the well. Haliburton, who's job is was to do the actual cementing, stopped and reported the tests to BP and Transocean. Haliburton and the other crew were placed on standby and told to wait. 40 minutes later, after the BP and Transocean company people broke huddle, they reported to Haliburton that an additional test had been performed and that it was OK to proceed with the final cementing. Haliburton was not shown any new test results, and it's a situation where many are questioning whether the test was performed at all.
So, to cement the well, heavy fluid gets pumped out of the pipes, weakening the well, and light fluid and sea water gets pumped in, further weakening it, and with a gas leak already going on, thar she blows.
Alarms went off and workers frantically scrambled to engage the blowout preventer, which is a really big set of emergency cutoff valves. However, the blowout preventer was leaking hydraulic fluid, was missing at least one battery, and one of the valves had been replaced with a useless testing part four weeks earlier when the blowout preventer was damaged in a smaller accident. Excellent.
Still, if someone had not continued to offload the heavy drilling mud, the blowout preventer would have never been needed. Seven hours of missing test data makes 8.5 missing minutes of Nixon Tapes seem tame. This will almost certainly result in legislation requiring real-time on-shore monitoring of rigs and testing.
