former forearc basin that was subsequently filled with sediments from submarine fan systems in the area, although most of the accreted sediments consist of coarse terrestrial clastics. In Arctic regions, natural gas hydrate deposits mostly occur in sand-rich units in association with permafrost. In contrast, gas hydrates in a marine environment tend to occur in continental margin sediments consisting primarily of fine-grained clay minerals and organic debris, which has settled onto the seafloor. They appear to be a very common constituent, filling spaces between the grains and within cracks and fissures in sediments on deepwater continental shelves where the temperature and pressure conditions are suitable for gas hydrate formation. It is generally believed that the majority of natural gas hydrate deposits around the world exist in fine-grained sediments in a dispersed and low-concentrated form, with hydrate saturations of between 1 and 12%. The low hydrate saturation can be explained due to the very small pore size and low permeability in clay-rich sediments, which hinder the mobility of both water and gas, necessary for hydrate formation (see UNEP Global Outlook on Methane Gas Hydrates (2012, in progress) for more details). In contrast, Japanese scientists were able to discover thick sequences of interbedded sands and muds while drilling on the southeastern coast on the margin of the Nankai Trough. Natural gas hydrates seem to mostly occur in high concentrations in the sand units, representing up to 70% of the pore space and are largely absent from the mud sequences. The Japanese Methane Gas Hydrate R&D Program at Nankai Trough The Japanese drilling project, part of the “Methane Hydrate Research and Development (R&D) Program”, is located in the Nankai Trough region along the southeastern margin of Japan. The production research well project was developed in this region after field surveys completed by the Japanese government in 1995 revealed the existence of a bottom simulating reflector (BSR), which is believed to indicate the existence of large subsurface gas hydrate deposits. The project aims were to understand the nature of methane hydrate-bearing sediments in the Nankai Trough, the gas hydrates’ role as a future potential energy resource, and to assess the production and properties of the gas hydrate and its stability. In order to produce methane from gas hydrates, the development of safe and dependable technology is very much needed, as dissociation of methane in shallow waters can produce very high pressures and cause submarine