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USGS Fact Sheet FS–021–01 dated March 2001, Natural Gas Hydrates—Vast Resource, Uncertain Future, in part, states that “[g]as hydrates represent a hazard to conventional oil and gas production. In the Gulf of Mexico, oil and gas exploration is extending into water depths where gas hydrates occur at the sea floor. Pumping hot oil from great depths through drill pipes can cause warming of sediments and dissociation of hydrate, liberating large amounts of methane, weakening sediments, and perhaps generating pockets of highly pressured gas. The result might be gas blowouts, loss of support for pipelines, and sea-floor failure that could lead to underwater landslides and the release of methane from hydrates.”
Perhaps the exothermic reaction of the concrete (i.e., the curing process) intended to cap the exploratory well helped trigger the formation of an enormous methane bubble that was ignited at the surface and triggered the cascading events that led to the Deepwater Horizon oil spill. The naturally-occuring (at depths below about 600 meters) methane clathrate hydrate would have been stable at the high pressure and cold temperature of the Gulf bottom. However, if this pressure was reduced or the temperature was increased (via, for example, the concrete curing), the methane hydrate would potentially "melt," and its trapped methane gas would rise and expand immensely.
It's interesting that a comprehensive risk analysis that explored this and other potential scenaria and their expected consequences wasn't required as part of the deepwater oil exploration permitting process.