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242 Managing Global Warming

reserved energy which can alleviate the energy crisis to certain extent [8,9]. Therefore,
how to exploit MH safely and efficiently has become a worldwide focus.

7.2 Production methods

The exploitation methods mainly include the chemical and physical methods. For
chemical methods such as chemical injection method, the diffusion of chemicals is
inhibited due to the low permeability of methane hydrate-bearing sand (MHBS)
[10], leading to low gas production rate. Moreover, the costs of chemical method
are high and not suitable for large-scale exploitation. These two defects make
researchers seek other more efficient methods. Physical exploitation methods, which
include thermal recovery and depressurization methods, have the advantage of low
cost and high gas productivity [11]. The aim of these two methods is to change the
environment of MH by either increasing the temperature or reducing the confining
pressure until the temperature-confining pressure condition is such that MH dissoci-
ates into methane gas and water, as illustrated in Fig. 7.5 [12,13].

7.2.1 Thermal recovery method
In this method, a well is drilled into the methane hydrate-bearing layer, and the meth-
ane hydrate is dissociated by heating, using a fluid (hot water or steam) heated at the
surface in a boiler or similar device and circulated down through the well, as illus-
trated in Fig. 7.6. This causes methane hydrate to dissociate and generate methane gas.

Fig. 7.5 The base condition to 0
form MH. Seawater
200

400 Phase
boundary
600 Temperature
Depth D (m) 800

1000

Seabed
1200
Formation area of
methane hydrate
1400
BSR
(Bottom simulating reflector)
1600
−30 −20 −10 0 10 20 30
Temperature T (°C)