Typical oil contains 5% methane which is simply burned off. However, the oil that is gushing from this super deep well contains 60% methane mixed with the oil. This is what was causing the methane hydrate cystals to form and which was part of the reasons which made capping the well impossible. Oceanographers from the University of Georgia are measuring methane in the water at 10,000 times the usual concentration whole oxygen is running at 40% it's normal concentation. As bacteria in the water feed on the methane and dispirsed hydrocarbon it consumes oxygen. Low oxygen levels create dead zones that will kill fish and marine mammals.
However, there is a much greater problem with huge amounts of methane being released. While carbon dioxide is not a green house gas, methane is a significant green house gas. While carbon dioxide is plant fertillizer, methane could cause global warming if there were enough released.
Some have suggested setting off a nuclear explosion to seal the gulf leak. A nuclear explosion is the worsth idea because that could fracture a huge reservoir of methane causing a toxic cloud that asphixiates all living things wherever it goes as well as possibly causing a tsunami. But even more worrisome is that if enough methane were released, that it could trigger global warming and a "Soylent Green"- like future.
What is needed is thermate or themite which is an incendiary and not an explosive. This stuff burns under water and can be used to melt the steal pipe and earth together and seal the fissures.