Dear Straight Dope:
Now that there are oil wells on fire in Iraq, how do those fires get put out? I'm under the impression it's a real pain in the ass, but I don't understand what they have to do differently from other fires. Do they have to order up unbelievable amounts of baking soda? --
It may come as a big surprise, but in most cases they don’t put out the fire. At least not like in the movies. Unlike the movie Hellfighters, John Wayne doesn’t turn up with a stick of dynamite. There is no explosion which results in oil-slicked rig workers cheering at an erupting spout of gas. They may have done that in the old days, but these days everything is a lot more boring.
In the vast majority of cases, putting out the fire is a low priority. There have even been cases where a well has been set on fire deliberately as a safety measure. Oil wells often produce large amounts of poisonous gasses, notably hydrogen sulfide, in addition to hydrocarbons. Ironically, if Saddam hadn’t set the Kuwaiti oil wells on fire during the first Gulf War, in some ways that would have been a bigger problem for the coalition. A lot of wells in the Middle East produce copious amounts of H2S.
Back to our story. The fire isn’t put out because the fire isn’t the real problem. The problem is the large quantities of oil and gas spewing out into the environment. There are two main ways of stopping the flow.
The quickest, cheapest and easiest method is to deal with the problem at surface. If the top bit of well (the wellhead) is accessible, then the normal procedure is to make a clean cut on the pipe and stick on a new valve. Close this valve and the oil stops gushing and the fire goes out. The most difficult part of this sort of operation is clearing away the debris from the burnt-out rig. This requires fire fighters, plenty of water and/or foam and all sorts of heavy equipment. Often a large pipe will be lowered over the wellhead. This is designed not to put out the fire but to direct the flame away from the guys working close by. After the first Gulf War the main difficulty in the Kuwaiti oilfields was digging through several meters of solidified oil that had pooled around the wellheads.
If that’s not a viable option, the alternative is a relief well. In this case a new well is drilled some distance away from the inferno. The idea is to tap into the problem well hundreds or thousands of feet underground. If you manage that, you can control the problem well from a safe distance. You just pump in drilling mud of sufficient density to stop the flow of oil and gas. Once again, stop the flow of oil and gas and the fire goes out.
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