Tidal Current Energy

Methane Hydrates
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1.1 . Occurrence
Methane hydrate forms at high pressure and low temperature, where sufficient
gas is present, and in generally two types of geological settings: in the Arctic,
where hydrate forms in and below permafrost, and beneath the ocean floor at
water depths greater than about 500 meters. The hydrate deposits themselves
may be several hundred meters thick. The resource contained in marine methane
hydrate deposits is significantly larger and occurs in many more countries
than do Arctic hydrates (see Figure 16.2 ).
1.2 . Resource estimates
Global estimates of the methane hydrate resource vary considerably, from
1 � 10 15 to 5 � 10 15 m 3 at STP [1] , to 21 � 10 15 m 3 [2] . This is significantly larger
than the estimate of global conventional natural gas resources of 44 � 10 13 m 3
[3] . The methane hydrate estimates are for gas in-place. Actual production
would be only a percentage of this volume. However, the potentially producible
volume could still be larger than with conventional natural gas resources.
What is perhaps more important is that methane hydrate resources occur in
areas of the world that do not have significant conventional hydrocarbons, notably
around the Pacific Rim. Production of methane from hydrate may be able to
provide indigenous energy supplies for countries that currently import most of
Depth/m
0
200
400
600
800
1000
1200
1400
1600
Geothermal
gradient
Phase
boundary
Depth of
permafrost
Base of
gas hydrate
Sediment
Methane
hydrate
�20 �10 0 10 20 30
Temperature/�C
Depth/m
0
200
400
600
800
1000
1200
1400
1600
Phase
boundary
Geothermal
gradient
Methane
hydrate
Water
sediment
�20 �10 0 10 20 30
Temperature/�C
Base of
gas hydrate
Figure 16.2 . Phase diagram showing the occurrence of methane hydrate in Arctic and marine
settings in relation to pressure and temperature conditions.
(Courtesy of S. Dallimore, Natural Resources Canada)