Not "why didn't the blowout preventer work?" Why did the rig explode? For a possible answer, check out the great graphic below. I find it fascinating, if nothing else, from a how-things-work perspective.
The drawing shows the construction of the Deepwater Horizon drill shaft (the hole into the ocean floor) and riser (the pipe from the hole to the rig). It also shows how the various concentric layers of the hole itself were drilled and were sealed (or not sealed). The source of the artwork, by the way, is Halliburton and the Times-Picayune (h/t bmaz at FireDogLake).
To read it:
- Start with the vertical sketch at the far left of the graphic. Note the oil rig at the top, then the riser (the pipe down through the water), then at 5321 feet, the start of the sea floor, the sediment and rock. All the way at the bottom of the drawing, three miles below sea level, is the money (sorry, the goo).
- Next look at the middle part of the drawing. It shows, top to bottom, the concentric — and increasingly smaller — holes that were drilled in the earth to get to the goo. At the bottom of the hole is the plug they put in prior to leaving the site, which they were about to do. Note also that the inner pipe is tapered. That turns out to be another indication of BP's haste to move on.
Keep in mind that this was a drilling operation, not an extraction job. The Deepwater Horizon was there to make a hole and seal it for later. The extraction crew could then come by anytime in a production rig, remove the plug at the bottom, and pump the money (sorry, goo) out of the hole. - Now that you're oriented to the picture's contents, read down the text at the right side of the drawing, starting at the top. It will explain how the concentric holes were drilled, cased, and sealed from each other with line hangers, so there were no gaps.
When you get to the bottom, linger. Note that in their haste to move the rig, they failed to put a line hanger (a seal) between the last two casing layers, the innermost ones. Oops. - Finally, imagine what would happen if natural gas, under pressure, got into that gap at the bottom. Just picture it — as the graphic says, it's a straight shot to the top.
Now glance at the top-left corner of the graphic again — at the Deepwater Horizon rig itself sitting on top of that pipe. Imagine the explosion if the rising and expanding gas burst into the rig from below — and found anything making a spark.
If the failure to seal the casing at the bottom occurred to save money, as recent reports indicate, that's criminal negligence and manslaughter. And if BP were human (sorry, were a human), that human would be looking at San Quentin or Sing Sing.
So, how do you put a Corp in Sing Sing? Can you even convict one in Mr. Robert's Neighborhood? Just wondering.
Yours in good engineering,
GP
(By the way, for you nostalgia fans, BP used to be AMOCO of Indiana back in the good old days. You know, when our oil companies used to rip off other people.)
