03
May
10

Is this an oil spill–not exactly

I’m a bit on the annoyed side with news agencies overplaying the current oil leak in the Gulf of Mexico and never really explaining what happened in clear language, so I will attempt to do so. I would like to clarify a few things which may be confusing to those not utterly saturated in the oil industry from a young age as I have been.

The Deepwater Horizon is known as a semi-submersible drilling platform. It does the drilling then gets out of the way for a production platform to come in and produce the oil from the well. It is a very, very expensive rig which Transocean lost quite a bit of money on. They drilled six holes (read: spent lots of money) and never made any hits with it (read: lost a lot of money). It was then leased to BP (probably to make up for lost money) and used to drill in the Mississippi Canyon area.

They are currently blaming the problem on the failure of something called a “blowout preventer” (BOP)–those of you not familiar with the oil industry would probably want to know what a blowout is first. A blowout is when oil or natural gas enters the drill string (the pipe that drills the hole) and flows back up through the drill string to the surface. This happens when the pressure at the bottom of the hole is greater than the weight of the drilling fluid (aka mud or slurry) to the top of the hole. This can happen one of several ways: an unexpected pocket of high-pressure gas may be reached, a fissure in the formation may cause drilling fluid to leak, or human error. All three of these are usually not a problem because of the BOPs currently used.

A BOP is not just one valve, but a series of valves to prevent the flow of material to the surface. The first to be used is the annular preventer, which stops the flow of returning drilling fluid and has a hole for the drill string. This is used when returning mud increases its returning velocity. Usually, increasing the pressure of the mud going into the pipe will be sufficient to stop the backflow of material.

If this fails, the second to be used is the shear ram which cuts the drill pipe and closes it off to the surface, if there is no pipe, the blind ram can be used instead of either of the two. These three are last ditch efforts to prevent a blowout (well, a blind ram can be used to just close off the hole if there is no pipe), and if they are being used, there has probably already been a series of mistakes. At the time of the explosion, they were cementing casing in the hole, which means there was no drill string in the hole at the time, so the blind rams or shear rams could have been used.

What likely happened is that they had just finished cementing the casing in place (via a process called “squeezing” and began to pump out the excess wet cement and did so too rapidly. This decrease in pressure caused the cement plug which had just been put in place to collapse resulting in a blowout. The sudden decrease in pressure and failure of the BOP to operate properly likely caused the blowout.

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