My granddaughter Alexis, 6 made a functioning model of BP’s Deepwater Horizon disaster in our back yard pool. She had a hollow foam “noodle” float, about 3 inches in diameter and 3 feet long. The game was to fill it with water, point it up in the air, and blow the water out the top like a whale spout.
It was hard to get the water started, because she was using her little lung power to lift a column of water about 3 feet high. When she got it moving, a little would trickle out of the top. Now there wasn’t as much water to lift, so it got a little easier. As she kept blowing, there was less and less water and it moved faster and faster until the last cupful or so blew out in a shower of drops with a satisfying “Poof!”
Now imagine the noodle as a couple of miles of pipe with the Deepwater Horizon oil rig at the top. At the bottom, playing the role of Alexis’ lungs, is a big pocket of oil and gas exerting thousands of pounds per square inch of pressure. Just like the noodle, it’s the weight of water in the pipe that keeps the oil and gas down, defeating the huge pressure that wants to escape. That may not be enough, so drillers keep the hole filled with heavy, gooey mud that is much harder to blow out than water alone would be.
But suppose the mud is a little too thin or the pressure below increases a little. Oil and gas move up a little, pushing mud out the top. Now there is less weight of mud holding the oil and gas down, so it moves up a little more, pushing out more mud. Just like the noodle, things move faster once they get started. Which means there is not much time to operate the infamous “blowout preventer,” seal the top of the pipe, and keep everything– mud, oil, gas – down in the hole.
It takes months to drill an oil well, and when you’re finished you slip a plug into the hole and pump in a load of cement to harden below the plug and seal the hole permanently. You want to do this fast, because you have a rig at the top of the pipe costing you hundreds of thousands of dollars every day, and doing nothing but keeping a hole filled with mud. This plug is not like bath tub stopper – it’s a huge chunk of metal that you’re poking around at the bottom of a mile-deep hole. If the plug doesn’t fit well, then concrete can leak past it, mud can settle into the concrete, and you only think your hole is sealed. BP had a lot of trouble getting their plug in place, which took time and put them behind schedule in getting that expensive rig on its way.
To check for leaks they did a “positive pressure test.” They pumped up the pressure and waited to see if it held or dropped. Just like Alexis’ float ring in the pool – if it stays firm, there’s no leak. If it gets floppy, there is. Trouble is, oil and gas flowing up from below can keep the pressure high, so you get fooled. A “negative pressure test” reduces the casing pressure and if any oil and gas is leaking, the pressure will go back up. If the pressure stays low, you know for sure there’s nothing coming through. This test would have proven that oil and gas was leaking. But they didn’t run it..
Based on the deceptive results of the positive pressure test, they started pumping out the mud and replacing it with sea water. The water weighed far less the mud so it exerted less pressure to hold down the oil and gas. Before switching mud to water, they could have put in a second concrete plug as a backup if the first plug leaked. But they didn’t.
So far there wasn’t a clear indication of a problem, just a lack of assurance that everything was OK. But that morning they measured more mud coming out of the hole than there was water coming in. Only way that could happen was if oil and gas was moving up and pushing the mud out. Knowing the physics of foam noodles, it won’t surprise you that the amount coming out was increasing. Even at this late point, there might have been a chance if they had started pumping heavy mud back in to push the oil and gas back down. They didn’t.
A while later they stopped pumping in sea water, and the pressure continued to increase – only way that could happen was if oil and gas was moving up. But no action was taken. A while later the pressure really shot up. It was reported that mud was flowing out of the hole so fast it was going over sides of the rig. Then the oil and gas reached the rig itself, and something ignited it.
This is a long story of assuming things are OK without real evidence, and of ignoring evidence that things are not OK. Before you get too mad at BP for these flaws, consider that this is pretty much the way we run our Federal government.
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