Minerals Report - International Seabed Authority

further pointed out that even if only a small percentage of this were
recoverable, it would constitute a major stock of energy.
Dr. Desa then turned his attention to how methane hydrates
deposits and the free gases found beneath them are formed. He pointed
out that with the correct pressure and temperature, and with enough gas
there is a good basis for the formation of hydrates. Dr. Desa said that subseabed
methane is produced primarily by microbial and thermogenic
processes. He said that in the microbial process, the organic debris of the
depositing sediments is decomposed by a complex sequence
(methanogenesis) into methane by bacteria in an anoxic environment. He
added that decomposition is thought to take place either by acetate
fermentation or by carbon dioxide reduction.
He stated that in the thermogenic process, thermal cracking of
organically derived materials takes place to form petroleum hydrocarbons
(including methane). He said that thermal cracking generally occurs at
considerable depth (>2km) in sedimentary basins where temperatures
exceed 100°C. He also said that thermogenic methane might also be
produced by thermal degradation of oil at even greater depths and by
maturation of coal.
Through the use of an illustration, Dr. Desa pointed out the gas
hydrate stability zone, which he said was of the phase boundary type. He
pointed out the locations of both free gas and hydrates in the diagram. Dr.
Desa briefly described how a geothermal gradient is formed, its
relationship with the phase boundary, and the possible thickness of the
gas hydrate zone. He said that the top of the zone is not accurately defined
because it is not known whether methane is to be found there, and
whether or not there is enough of it to produce hydrates. Dr. Desa
informed participants that the National Institute of Oceanography of India
has produced a stability zone thickness map for India for an oil company.
He showed participants a map of the maritime areas of India containing
this information, and said that scientists produced this map by
synthesizing data such as the bathymetry of the seabed, seabed
temperature, the geothermal gradient, organic carbon and sediment
thickness. He said that a big oil and natural gas cruise in India’s maritime
areas is planned to investigate some of the findings.
Turning his attention to a phase diagram of a hydrate deposit, Dr.
Desa stated the need to examine this diagram in relation to the stability
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