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Methane Hydrate
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Factors Required to Form Deposits |
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Factors Required to Form Deposits
First, a gas must be present.
Under geological conditions there are two major sources for
gas production. Either the gas is produced
thermocatalytically as a result of breakdown of organic
carbon to oil and gas, or gas is produced bacteriologically
by relatively shallow decomposition of organic matter.
 The
type of organic carbon deposited also plays a role here;
terrestrial plants tend to have high wax and sulfur contents
in order to retain water during their lifetimes and also to
provide a rigid stem. Marine plants need neither of these
conditions. Thus if bacterial action is on terrestrial plant
debris then H2S, CO2, CH4 are dominantly produced, while if
on marine vegetation then methane and carbon dioxide are the
main gas products.
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Second, once gas
is produced, it must find a migration pathway from the
source region to the geological regions favourable for
hydrate formation.
 Third,
all gases are soluble in water to greater or lesser degrees
with the solubilities being pressure and temperature
sensitive plus also being dependent on what other gases,
minerals, molecules, ions and compounds are dissolved in the
water and on the concentrations of each such component. Thus
there is an excruciatingly complex transport problem for
gases in their journey to the sedimentary surface with
geological time, and there is also a problem of whether the
gaseous concentration of, say, methane will exceed the
solubility limit and so appear as free-phase gas, which has
its own transport and buoyancy characteristics that are
different to those of gas in water solution. |
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