In March 2013, the world's first field trial of gas production from marine methane hydrate deposits was conducted in the Daini Atsumi Knoll area of the Eastern Nankai Trough off the Pacific coast of Japan as a process to bring gas hydrates under seafloor to valuable energy resource. The technique used to dissociate the ice-like material was "depressurization method" that had been applied in the previous production test in Mallik site, the Northwest Territories, Canada in 2007-2008. Japan Oil, Gas and Metals National Corporation (JOGMEC) as a part of MH21, the Research Consortium for Methane Hydrate Resources in Japan planed and supervised the project with the funding of the Ministry of Economy, Trade and Industry (METI), and scientific supports from the National Institute of Advance Industrial Science and Technology (AIST). One production well with two monitoring boreholes were drilled in the test site for the test. Along with the flow test operation, intensive data acquisition program was planned and implemented to understand behavior of methane hydrate dissociation- bearing sediments against depressurization. To realize high degree of drawdown in relatively shallow formation below deepwater, several downhole devices were designed and installed. The flow test started in the morning of March 12 and lasted until severe sand production forced to terminate the operation six days later. During the stable production term, gas flow rate was approximately 20,000m3 under atmospheric condition, and gas liquid ratio was larger than 100. A lot of data including formation temperatures, fluid pressure and temperature, and physical property changes in the formation were obtained. The data taken are under studies to verify applicability of the depressurization technique as a methane hydrate production technologies.

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The JOGMEC/NRCan/Aurora Mallik gas hydrate production tests were conducted using the depressurization method in April of 2007 and March of 2008. These tests represent the first and so far only successful sustained production in the world of methane gas to surface from a gas hydrate reservoir by depressurization. A variety of data, such as wellhead/bottom-hole pressure and temperature, gas/water flow rates, and temperature along the casing measured by distributed temperature sensing, were acquired during the tests. The flow rates of gas and water from the reservoir sand face during the tests were estimated by comprehensive analysis of these data. Diverse history-matching simulation was then conducted to reproduce these estimated flow rates, using the numerical simulator MH21-HYDRES coded especially for gas hydrate reservoirs. This series of history-matching simulation studies quantitatively clarified the mechanisms of methane hydrate dissociation and production, as well as what had happened in the reservoir during the production tests. This paper describes the procedures and results of a series of these studies, including the analyses of production-test data, numerical modelling and history-matching simulation, which will provide beneficial insights into the mechanisms of methane hydrate dissociation and production for future exploration and development planning for gas hydrate resources.