28 / 96
FROZEN HEAT
28
Gas hydrates occur broadly throughout Earth’s deep-water
continental margins and in areas overlain by thick perma-
frost (see Volume 1 Chapter 1). They represent a massive nat-
ural storehouse of methane gas and hold significant poten-
tial as a future energy resource. Though no commercial-scale
extraction of methane from gas hydrates has yet occurred,
developing the necessary tools and techniques appears plau-
sible given recent advances in hydrocarbon recovery capa-
bilities. For example a number of previously inaccessible
hydrocarbon resources are now being tapped – reservoirs
9 000 metres deep and in 2 500 metres of water (Cunha
et al.
2009) and gas trapped in deep shale formations once
thought to be unproduceable.
However, as with any component of the global energy re-
source base, gas hydrates do not occur in the same manner
everywhere. Some deposits, due to the nature of their geo-
logic settings, will be more promising targets than others.
A number of highly variable and location-specific factors in-
fluence the nature and development potential of gas hydrate
reservoirs. These include the local supply of methane gas, the
configuration of pathways for gas to migrate and concentrate,
the presence and extent of the zone in which pressure-tem-
perature conditions allow gas hydrates to form, the nature
and properties of the host sediments and their capacity to
hold rich accumulations, and the regional geology that pro-
vided the time and conditions for gas hydrates to form and
to persist as significant accumulations. Because these factors
vary significantly, even at a local scale, gas hydrate occurrenc-
es are highly variable (Fig. 2.1). Therefore, while it is likely
that Earth contains enormous volumes of methane within
gas hydrates, it is also likely that only a small percentage of
that gas exists in a manner that makes extraction technically
and/or economically feasible, at least in the relatively near
future (Text Box 2.1).
This chapter reviews some key issues in understanding the
energy supply potential of gas hydrates. We discuss the best-
studied sites where gas hydrates have been evaluated, rang-
ing from the most promising sites to the most problematic.
Then, in Chapter 3, we discuss the leading means by which
these reservoirs might be produced.
2.1
INTRODUCTION