FROZEN HEAT | Volume 2

3.4 GAS HYDRATE PRODUCTION

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).

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

While no commercial gas hydrate production has yet been attempted, several scientific field tests have been carried out

Gas hydrate production method

Pressure, Megapascals

0

Depressurization

Thermal injection Inhibitor injection

Liquid + Gas

Water or steam in

Methanol in

Depressurization

5

Gas out

Gas out

Thermal stimulation

10

Hydrate cap

Impermeable rock

Chemical stimulation

Hydrate

Dissociated hydrate

Dissociated hydrate

15

Free gas

Gas hydrate + Liquid

Impermeable rock

20

0

5

10

15

20

Temperature, ºC

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.

FROZEN HEAT 68