[a real Sheila]

won’t they still have the “methane crystals” issue to deal with if they have to use this method?

If NOT, then why didn’t they do this in the beginning?

[Sudetenland]

No, the methane crystals form in the flow coming out of the well. Methane is a gas which is part of the fluid in the reservoir. At the high pressures in a reservoir and in the pipe, it is a liquid. As the pressure is relieved from the fluid, the gas and oil components separate and the gases expand. Problem is that it is very cold at that depth in the ocean, and as gases like methane expand they cool. This causes the ice crystals to form plugging the lines they use for collecting the fluid.

What they are doing with the topkill, is forcing a heavy mud to backflow down the pipe to plug the well. This will keep the reservoir fluid (oil and gas) in the reservoir (formation) and there will be not gas or oil flowing out to form those crystals.

Hope this helps.