SIZE OF THE GLOBAL METHANE HYDRATE ENDOWMENT

Evidence suggests that the amount of methane sequestered in gas hydrate is large, but just how large is a continuing debatable issue. Estimates range from early (1980) values of 7,600 x 10¹⁵ m³ to recent (2000) values of 0.2 x 10¹⁵ m³. A ‘consensus’ estimate of 21 x 10¹⁵ m³ is about 50 times larger than the global endowment of conventional methane gas of 0.44 x 10¹⁵ m³. However, this comparison is questionable because the underlying assumption is that the conventional methane is ultimately recoverable for energy purposes, whereas only an unknown, but likely small portion, of the hydrate methane will become available for exploitation. Thus, the size of the exploitable methane hydrate endowment may not differ greatly from the conventional methane endowment. Recent considerations by others suggest that the total amount of hydrate methane is less than the consensus estimate by factors ranging from 3 to 100. If these lower estimates are more realistic than the consensus estimate, then the amount of hydrate methane available for postulated roles in global climate change, submarine geohazards, and energy resources is greatly reduced. Therefore, knowledge of the amount of exploitable versus non-exploitable hydrate methane is critical for developing valid concepts about possible geological roles for methane hydrate.