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A release of methane gas in deepwater undergoes a series of physical chemical processes as it rises from the deep to shallow water in the form of a plume. A key process is the formation of methane hydrate in the deep and the eventual hydrate dissociation when the plume reaches shallower regions of lower pressure and higher temperatures. This paper presents a model to simulate the behavior of methane gas released in deepwater. The model considers all processes that gases undergo when released in deepwater under high pressure and low temperature conditions. In addition to including the complete plume hydrodynamics and thermodynamics in the model, it takes into account the processes like hydrate formation and dissociation, gas dissolution, hydrate dissolution, break-up and coalescence of gas bubbles, and the possible separation of gases from the main plume. Scenario simulations using the model are also presented in this paper. The model is suitable for environmental impact assessment and contingency planning.

From 2001, the Japanese government has had a national project, conducted by Research Consortium for Methane Hydrate Resources in Japan, which has been promoting methane hydrate exploitation under the seabed in the deep sea of more than 1000 m depth in Japanese EEZ. This paper briefly describes the development of the monitoring technology, by one of the R&D sub-group of Environmental Impact Assessment Group of the Consortium that is conducted by Engineering Advancement Association of Japan, including both sensor technology and integration technology of the monitoring system in the deep sea on some possible factors which can badly affect to the environment around the methane hydrate production area in the future. Regarding sensor technology, we have had great efforts to develop high-performance sensors for dissolved methane and seafloor displacement, which we thought had not been well developed during our pre-investigation several years ago. As to integration of the total monitoring system, at first, we studied well what items to monitor, how to monitor and how accurate to read. According to the results, we studied the existing related technologies including installation units i.e. mooring type and AUV, electric power supply, data transportation, installation/removal method and so on, so that we could successfully reach some conclusion on total concept of the integrated monitoring system. Based on the concept, we also successfully completed the study on a necessary integrated monitoring system that shall be deployed with the well-developed sensors at the ocean production trial that is planned to carry out in the future.

Japan relies on imports for the greater part of its energy needs, so that securing reliable future energy resources have become even more significant due to the recent violent fluctuation in the price of oil. In addition, as global environmental problems, such as global warming, become more serious, the need to shift to cleaner energy sources, such as natural gas, becomes more pressing. In this social context, methane hydrate, a new natural gas resource that has been confirmed to exist in the sea surrounding Japan, is expected to become a cleaner source of domestic energy in the future. Methane Hydrate Exploitation Program in Japan was published in July 2001 and the Research Consortium for Methane Hydrate Resources in Japan official abbreviated title MH21 Research Consortium was established to oversee the completion of phase-1 of this plan. In this consortium, Engineering Advancement Association of Japan official abbreviated title ENAA , which is the group responsible for conducting Environmental Impact Assessment, EIA, has conducted a number of research and developed activities to establish basic technologies associated with EIA and completed almost all of aims during phase-1. In this paper, we introduce overview of our R&D about EIA which should be necessary to implement on methane hydrate production.