FROZEN HEAT | Volume 2

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).

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

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