• Tunnel and Underground Space
• /
• v.25 no.2
• /
• pp.133-143
• /
• 2015

Gas hydrate is a solid substance composed of natural gas constrained in water molecules under low temperature and high pressure conditions. The existence of hydrates has been reported to be world-widely distributed, mainly at permafrost and deep ocean floor. Test productions of small amount of natural gas from the on-shore permafrost have been accomplished in U.S.A and Canada, but, world-first and the only production case from off-shore hydrate bearing sediments was in Nankai trough, Japan. In this study, we introduce key technologies in gas production from hydrates by analyzing the Japanese off-shore gas production project in Nankai trough in terms of depressurization- induced dissociation so as to utilize planned domestic gas production test in Ulleung basin.

• Economic and Environmental Geology
• /
• v.47 no.3
• /
• pp.275-289
• /
• 2014

Recent scaled-up onshore and offshore field production tests revealed that the expectancy to produce gas from the gas hydrate deposits is gradually increasing, recognizing its potentials as one of the future energy resources. The total produced gas was approximately $480m^3$ by the hot water circulation method for 6 days' operation in Mallik 2002 project in Canada. In Mallik 2006-2008 project, the gas was successfully produced stably by the depressurization method for 6 days, up to $13,000m^3$ cumulatively. The depressurization method applied in the Mallik test was revealed as an effective way to produce gas from gas hydrates. The Alaska North Slope field trial in 2012 to inject mixed gas of $CO_2$ and $N_2$ to exchange $CH_4$ was successfully completed for the first time to produce maximum $1,270m^3$ per day. The remarkable achievement is that Japan has completed first offshore production test in the Eastern Nankai Trough, and produced approximately $120,000m^3$ of methane by the depressurization method for 6 days in March 2013. The technical challenges and uncertainties obtained from Nankai Trough production test give Korea more considerations in the aspects of well completion, reservoir formation and seafloor stability, sand control, flow assurance, and etc., due to the different geological environments and geomechnical properties in Ulleung Basin in Korea.