The question is in the title, but why did the rig blow up and sink? The leak is a mile away. Or did the sinking of the rig cause this? A bit of both?
The rig blew up because of a blowout. A blowout occurred, at least partly, because the blowout preventer failed to work correctly. The sinking of the rig caused the riser (the one mile long vertical pipe from the well to the rig on the surface) to bend and break, causing the bulk of the leak. The riser pipe is now sitting broken on the ocean floor.
I don’t think anyone knows exactly why the rig blew up - the investigation is ongoing, and it’s not going to be easy to determine the exact cause, with the destroyed rig sitting under a mile of water.
The explanation that I heard was that a bubble of high-pressure methane escaped from the pipe, and this then caught fire and caused the rig to sink.
It’s pretty much a given that the plugging operation failed and methane gas entered the riser and blew the rig up. The 60 minutes interview with one of the survivors was pretty thorough.
This WSJ article has some eyewitness accounts of what was going on at the time. From what I gather, there was a blowout (as already mentioned) and the gas which was coming up from below ignited. I have read speculation about what might have ignited it but I don’t think it’s possible to tell right now.
The initial leak occurred at surface, that is, at deck level on the rig, not at the seabed. After the rig sank, the riser pipe connecting the rig to the subsea wellhead sank with it; that’s why the main leakage point is now at seabed and some distance from the wellhead.
To be a little bit pedantic, the rig exploded because the blowout released a large amount of methane gas into the atmosphere around the rig, and when the methane concentration reached the lower explosive limit (approx. 5% in air), something ignited it. The ignition source could have been any number of things, including sparks emitted from metal objects striking each other or from damage to energized electrical equipment. Although all electrical circuits within a certain distance from the wellbore have to be specially engineered to prevent accidental ignition of a hazardous atmosphere, in this case witness reports seem to indicate that the methane vented from the well made its way into areas normally considered safe and were therefore lacking in such protection.
Other possible ignition sources were the diesel engines used to provide rig power. It is known that the methane had reached the engine room just prior to the explosion.
60 Minutes had a report. Virtually all the safety measures failed one by one and BP continued to drill despite insufficient safety measures being available. The 60 Minutes report will piss you off.
The employee on the 60 minutes interview said the gas was sucked in by the generators and they raced out of control causing overloads. that may have been one source of ignition. There was so much pressure that bulkhead doors were blown off their hinges.
Just want to say thanks. I thought the blow out occured at the sea floor.
The blow out occured deep in the well. The current best guess is that a cement seal that had just been set to close the bottom of the well was breached. Much finger pointing and speculation as to whether the seal was adequately designed, allowed long enough to set, or adequatley tested. They tested it twice. First time it appeared to fail, but with some ambiguity, so they tested again with a different setup that avoided a particular way the test could give a false negative. This time it passed. However it seems that the seal was indeed faulty, and it did fail.
The oil has methane under enormous pressure dissolved in it. As this rises the methane expands many hundred fold. The effect is like shaking a soda bottle. As the oil/gas rises the expanding methane accelerates the flow, and shoots everything out of the well, up the casing and up to the rig. That is where the explosion occured. But the well failure was deep underground.
The blow out could have been avoided at a number of points. Annedotal data suggests that many other wells have gone this far in the gulf. What failed in the Deepwater Horizon well was the last bit. They didn’t realise the well was kicking back in enough time. The device of last resort - the blow out preventer didn’t close properly. They are not strong enough to be able to cut through the joins in the drill pipe, and by bad luck the guess is that it closed on one of these joins - thus leaving an opening. That is why we have a leak and why gas continued to flow to destroy the platform.
It will be quite some time before a full understanding of the accident is had. Sensationalist TV programs are not the best source of information.
not a oily anything and moderate mass media news follower.
aren’t there sequential points to the preventer to pinch the pipe in order to give a seal and account for a coupling in the path? i think that an additional point was disabled and repurposed because it wouldn’t be needed in the optimistic view of those involved.
Another thanks.
I’ve had experience pumping concrete (just a little, home owner stuff). One time, a bubble of air got mixed in and pushed the concrete for a 100 feet or so under great pressure.
When the air bubble overcame the resistance of the concrete in the 4” hose it pretty much shot it out all at once. Sort of an immediate stucco on my brothers house.
There are. However there is only one set of shear rams. These are the real safety device of last resort. These were not modified.
It appears that BP had requested a modification of one set of blind rams (out of four) to be replaced with test (short) rams. This allows them to be tested without actually shutting down the well. It isn’t clear what the implications of this is. It seems to be used as some sort of evidence of bad behaviour of BP’s part, that they would modify a safety system like this. But it isn’t clear that it mattered. Nor that it is an unreasonable thing to do.
The BOP was required to be tested once every two weeks. It seems likely (to me anyway) that the modification allowed the test to proceed without the need for expensive downtime on the rig. You can still show that the BOP activates, the hydraulics work, the rams move, the end to end control systems are good, and that the emergency activation works. Which sounds pretty reasonable. It is a cost/benefit/risk issue. But there is no suggestion that they were actually working outside of accepted safety practices in doing this. The BOP has four sets of blind rams, one set of shearing rams, and above that the riser package has annular seals. It is the job of the shearing rams to cut through everything and seal the well. Needless to say you can’t usefully test this ability on a regular basis. Activating the shearing rams causes millions of dollars of damage. The blind rams also seal the well but can’t be used if there is a drill string in the way. Since there was a drill string in the well the blind rams would not have helped.
There is discussion about the Brazillian’s “show me” rule, where you have to demonstrate that the shear rams you will install are capable of cutting anything in the well before they will let you drill. The deeply disturbing issue is that a report three years ago from the MMS showed that 50% of the BOPs in use in the GM were not capable of cutting through and would fail to seal. And yet nothing was done. If you want a smoking gun on negligence, you could start there.