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FROZEN HEAT
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Unlike the Nankai Trough, the northern Gulf of Mexico hosts
a prolific petroleum system that continues to yield large con-
ventional oil and gas discoveries. Nonetheless, althoughmore
than 1 200 wells had been drilled through the gas hydrate
stability zone in the deep-water Gulf of Mexico by the end
of 2005, observations of gas hydrates in the basin had been
largely limited to sea-floor features associated with cold seeps
(Boswell
et al.
2012). An early assessment (Collett 1995) of
gas hydrate resources assigned more than 991 trillion cubic
metres gas-in-place to the basin. As indications of sub-sea-
floor gas hydrates were observed and as industry began to
investigate gas-hydrate-prone deep-water areas, concern over
potential drilling hazards increased. That led to the formation
of an international industry research consortium to address
gas hydrate issues in the Gulf of Mexico (McConnell
et al.
2012). Information gained during a 2005 drilling expedition
(Ruppel
et al.
2008) addressed many of these questions, and
attention has increasingly focused on gas hydrate resource
appraisal. In 2008, vast volumes of industry well and seismic
data were accessed to provide a comprehensive evaluation of
the potential for gas generation, migration, and trapping in
hydrate form (Frye 2008). This study determined that of 607
Figure 2.7:
Exploratory drilling and extensive geophysical surveys in the Nankai Trough. Drilling and surveys conducted in the Nankai
Trough, off the southeastern coast of Japan (left), have discovered thick sequences of gas hydrate in reservoir-quality, sand-rich sediments.
The gas hydrate adds significant strength to the sediment, resulting in the strong seismic reflections where the sand-rich units extend
upwards into the gas hydrate stability zone (right). Reservoirs such as these are the subject of the world’s first deep-water gas hydrate
production tests, which Japan began conducting in early 2013 (Images courtesy JOGMEC).