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The major advances in understanding the drilling behaviour of in
situ gas hydrates have come through field programs dedicated
specifically to the study of gas hydrates. Substantial resources
have been devoted to gas hydrate research and development
over the past several decades (Collett
et al.
2009), with more
than 100 dedicated gas hydrate wells successfully drilled to date.
Several Integrated Ocean Drilling Program (IODP) expeditions
have investigated gas hydrate occurrences along active and
passive continental margins. Multi-well exploration campaigns
have been undertaken by national gas hydrate research programs
in Canada, China, India, Japan, Korea, and the United States.
In addition, dedicated research and development programs
Box 3.1
Gas hydrate coring and drilling studies
conducted offshore Japan and in permafrost settings in Canada
and Alaska have tested the effectiveness of gas hydrate drilling,
coring, and cementing technologies. The Japanese program
included a short horizontal well in gas-hydrate-bearing strata 350
metres below the sea floor (Takahashi and Tsuji 2005). At the
Mallik site in the Canadian Arctic, a full-scale thermal production
test was completed in 2002 (Dallimore and Collett 2005). Gas
hydrate production by depressurization of the reservoir was
tested there during successive winter programs in 2007 and
2008 (Dallimore
et al.
2012). In Alaska in 2012, an advanced
production test program involving carbon dioxide injection and
pressure drawdown was completed (Schoderbek
et al.
2012).
largely overcome these problems by introducing modifications
to the drilling procedures and equipment, including:
• Chilling the drill mud to reduce thermal disturbance of
the formation;
• Managing the weight of the drill mud to achieve sufficient
downhole pressure to stabilize the in situ gas hydrates,
while remaining below the pressures that might fracture
downhole formations;
• Using chemical additives (or avoiding dissociation-induc-
ing inhibitors such as salts and alcohols) in the drill mud
to maintain gas hydrate stability in the formation and pre-
vent gas hydrate dissociation in the drill cuttings;
Figure TB-3.1:
Notable gas hydrate field programs. This is a general representation of notable hydrate field programs that have
been or are taking place around the world. The compilation is indicative and does not necessarily depict all hydrate field programs.
Prudhoe
Bay area
Mallik test site
Northern Gulf
of Mexico
Blake Ridge
Svalbard
Indian
Ocean
Ulleung Basin
Qilian
Mountains
Eastern
Nankai
Trough
Shenhu
Basin
Gumusut-
Kakap
Taiwan
Messoyahka
New Zealand
Cascadia Margin
Japan Sea
Mexico
Costa Rica
Peru
Selected gas-hydrates study areas