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FROZEN HEAT
68
Three primary gas hydrate production concepts have been
proposed to date, all based on the concept of in situ disso-
ciation of gas hydrates to release free gas that can then be
delivered to the surface (Figure 3.4). The depressurization
technique dissociates gas hydrates by reducing local forma-
tion pressures, the heating technique raises the formation
temperature, and the chemical stimulation technique chang-
es the chemical equilibrium conditions (Makogon 1997).
While no commercial gas hydrate production has yet been
attempted, several scientific field tests have been carried out
in the Arctic. A full-scale thermal stimulation test was un-
dertaken by a five-country consortium in 2002 at the Mal-
lik gas hydrate field in the Mackenzie Delta (Dallimore and
Collett 2005). At the same site, depressurization testing was
undertaken by a Canada-Japan research program in 2007
(Dallimore
et al.
2008a, b; 2011; Numasawa
et al.
2008) and
2008 (Yamamoto and Dallimore 2008). Additional data use-
ful for evaluating gas hydrate production potential are avail-
able from short-term drill-stem tests conducted by industry
in the 1970s (Bily and Dick 1974) and from small-scale for-
mation tests conducted as part of the 2002 Mallik program
3.4
GAS HYDRATE PRODUCTION
Figure 3.4:
Production methods and impacts on gas hydrate stability. For each of the three proposed gas hydrate production methods (left
frame), conditions within initially stable hydrate-bearing sediment are shifted such that hydrate at that location is no longer stable, and
will begin dissociating. Right frame: Depressurization: achieved by reducing the formation pressure below equilibrium limits. Thermal
stimulation: achieved by increasing the formation pressure beyond equilibrium conditions. Chemical stimulation: changes in gas hydrate
equilibrium conditions are induced by inhibitor injection.
Free
gas
Dissociated
hydrate
Dissociated
hydrate
Hydrate
cap
Hydrate
Impermeable rock
Impermeable rock
Gas out
Gas out
Liquid + Gas
Thermal
stimulation
Chemical
stimulation
Gas hydrate + Liquid
Temperature, ºC
Pressure, Megapascals
20
0
5
10
15
20
15
10
5
0
Gas hydrate production method
Depressurization
Water or
steam in
Methanol
in
Depressurization
Thermal injection Inhibitor injection