Hydrate Heat Effects The latent heat for gas hydrate formation and dissociation is large. The
formation of gas hydrates is an exothermic process, and its dissociation is an
endothermic process.
This means that during their formation the latent heat is removed to the
surroundings, increasing the temperature of the remaining fluid, thus limiting
hydrate formation.
This is why pipeline insulation could be an effective way of reducing the extent
of gas hydrate formation. However, during their dissociation heat should be
supplied to the system and simple depressurisation or inhibitor injection may
not be adequate for gas hydrate dissociation, as is discussed later.
Figure 4: Pressure-Temperature Diagram for Methane Hydrate.
Hydrate Stoichiometry Gas hydrates are non-stoichiometric compounds and this means that they do
not have a fixed formula. Gas hydrates, though a combination of gas and
water, are different from mineral hydrates that have a fixed hydration number:
the number of moles of water in the system is constant; but the ratio of gas to
water in gas hydrates is not constant.
Although each gas hydrate structure has a fixed number of water molecules
and cavities which can be filled with gas molecules, not all the cavities need to
be filled to stabilise the gas hydrate structures.
0
500
1000
1500
2000
2500
3000
3500
4000
4500
-10
-5
0
5
10
15
20
25
Tem p (oC) Pr es su re Ps i Roberts 1940
Deaton&Frost 1946
Kobayashi 1949
McLeod&Campbell 1961
Marshall&Kobayashi 1964
Jhaveri&Robinson 1965
Gallow ay 1970
Falabella 1975
Verma 1974
de Roo 1983
Thakoe&Holder 1987
