We have been developing a monitoring system for seafloor deformations during Methane Hydrate production test. Seafloor deformations are evaluated by measuring subsidence and inclination of the seafloor. Subsidence is measured with change of water pressure on the seafloor. As a sensor for the selected pressure gauge, quartz crystal resonator is applied. The range of the pressure gauge is 0 to 1,400 m, the resolution is 0.014 mm, and actual accuracy is around 10 mm in conversion to water level. As a sensor for the selected inclinometer, liquid electrolyte is applied. The range of the inclinometer is ±30 degree, resolution is 0.001 degree, and actual accuracy is around 0.02 degree depending on measuring condition. According to simulation of seafloor deformation around the production well, the range of subsidence will be from 10 cm to 30 cm. This system has been examined in the offshore of Suruga Bay which has water depth more than 1000 m. All the features of this system were confirmed by examination of deep sea area in Suruga Bay We will do a final check prior to the production test of Methane Hydrate at East Nankai trough on the end of FY2012.

This work was carried out by OYO Corporation with the support of JOGMEC which is a member of MH21 consortium sponsored by Ministry of Economy, Trade and Industry in Japan

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