Oceanic gas hydrates have received much attention because the global estimate of methane gas in these hydrates is 2–10 times larger than the ultimate recoverable resources of conventional natural gas. Especially, the gas hydrates in offshore Japan is expected to be a valuable domestic resource. Toward its development the Ministry of Economy Trade and Industry (METI) launched a "Japan's Methane Hydrate R&D Program" in 2001 and currently the research stage has been in progress to the implementation of the first offshore production test.
In our research so far, we established the methodology to delineate gas-hydrate concentrated zones and found more than ten hydrate-concentrated areas in the eastern Nankai Trough, which were estimated to bear gas hydrates equivalent to approximately 0.57 trillion m3 (20 tcf) of methane gas in place. To evaluate gas-hydrate well productivity and production technology, the first offshore production test was conducted in the waters off the coasts of Atusmi and Shima peninsulas in March 2013. One production well and two monitoring wells were completed in gas-hydrate-bearing turbidite sands at a depth of approximately 300 m below the sea-floor in about 1000 m of water. Gas production was obtained easily upon depressurization using an electric submersible pump (ESP) with gravel pack completion. We succeeded in about six-day continuous gas production of up to about 120,000 m3 (4.2 mmcf) for an average rate of 20,000 m3 /d (706 mcf/d).
The reservoir response and environmental impact during the gas production test is now under analysis, but it is safe to say that this world's first offshore production test opened the door of commercial production from offshore hydrates. This paper gives an overview of Japan's R&D activities and technical problems to be overcome toward future commercial production from gas hydrates.