Now we come to what the BP team believes were the causes of the accident, and the first company in the line of fire is Halliburton, which was the contractor responsible for the cement job to seal the well.
There is a heavy emphasis placed on the cement “foam”: cement injected with nitrogen to make it lighter, to avoid damaging the rock formation of the reservoir and making it harder to subsequently produce oil.
Because Halliburton, which provided the cement, has refused to provide samples for testing, the BP team has had to go to a third party company to produce a “representative” sample of a similar product, which was “the best we could do under the circumstances”, the investigator says.
In testing, the cement allowed oil and gas to escape much more than it should have done, and the team identifies cement failure as one of the key contributory causes of the accident.The next company to come under scrutiny is Transocean, which owned and operated the Deepwater Horizon rig.
One of the team members details the final hour or so before the explosion. It is believed that the oil and gas leak started around 8.52 pm, and after 9 pm pressure readings started to show some potentially worrying indications, but the seriousness of the problem was not appreciated until about 9.40 pm, when mud was blown onto the floor of the rig by the gas shooting up the riser (the pipe connecting the well-head on the sea bed to the rig on the surface.)
At that point, the workers on the rig began to respond, but they did the wrong thing: they diverted the flow of oil and gas towards a piece of equipment that did not have nearly enough capacity to cope with the volumes that were escaping. Overwhelmed, that equipment – the mud-gas separator – allowed gas to spread out over the rig. If the rig workers had instead simply diverted the flow over the side of the rig, the explosion might still have been averted.
Then comes the most harrowing part of the presentation, showing how the gas spread throughout the rig before igniting. A computer animation shows how in just four minutes, from 9.46 to 9.50, the rig became “enveloped in gas”, as the BP investigator put it. The gas escaped into the engine room, where the power generators went into overspeed. At 9.49 the first explosion hit, probably ignited by the generators, with a second coming ten seconds later.
Eleven men were killed and 17 more rig workers were injured. Having seen the scale of the gas cloud, depicted blue in the computer animation, it looks as though the death toll could have been much higher. 115 people escaped alive.