60 / 96
FROZEN HEAT
60
If economic and environmentally responsible production of
gas hydrate resources proves achievable, the global conse-
quences are potentially far-reaching. Natural gas emits sub-
stantially less greenhouse gas thanmany other fossil fuels – up
to 40 per cent less than coal or oil (EIA 2013). It has, therefore,
been identified by many countries as a preferred energy source
over other hydrocarbons for the near future. Gas hydrates are
thought to occur in relative abundance (in terms of the size of
the resource) in select locations around the world. They occur
in both marine and permafrost settings where methane gas
and water co-exist at pressures and temperatures suitable for
hydrate formation and stability (Figure 3.1).
3.1
INTRODUCTION
Depth (metres)
0
Depth (metres)
0
200
400
600
800
1000
1200
1400
1600
200
400
600
800
1000
1200
1400
1600
20
0
01
3
0
Temperature ºC
gnittes tsorfamreP
gnittes eniraM
-30
-20
-10
0
10
20
30
Temperature ºC
Base of permafrost
Stability zone
Stability zone
Stability conditions for gas hydrates
Ground surface
Ice freezing temperature
Sea surface
Sea oor
Figure 3.1:
Phase diagrams illustrating where methane hydrate is stable in marine (left frame) and permafrost settings (right frame).
Hydrate can exist at depths where the temperature (blue curve) is less than the maximum stability temperature for gas hydrate (given by
the hydrate stability curve in orange). Pressure and temperature both increase with depth in the Earth, and though hydrates can exist at
warmer temperatures when the pressure is high (orange curve), the temperature in the Earth (blue curve) gets too hot for hydrate to be
stable, limiting hydrate stability to the upper ~1km or less of sediment.