Methane hydrate
As with geological formation, methane hydrate bearing layers are subject to be pressurized by the combined overburden weight of seawater and the formation pressure. In drilling for formations subjected to such pressures, it is customary to use a drilling mud with a specific gravity higher than this pressure. Conversely, the depressurization method lowering the pressure inside the well and encouraging the methane hydrate to dissociate. (Methane hydrate dissociates into methane gas and water when depressurized.)