Evaluation of Mechanical behaviour for Resources Development of Methane Hydrate-Supported Sand in Deep Seabed

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The possible existence of a vast amount of methane hydrate around islands has attracted attention in Japan. At the same time, several production methods have then considered to extract the gas from the hydrate zone. Although it is known that the hydrates pose significant obstacles to drilling and production operations, them is at present only limited knowledge on the mechanical behavior of hydrate-rich zones, which is necessary to understand the stability around the site. For this purpose, a low-temperature high-pressure triaxial test equipment was developed to reproduce the temperature and pressure condition of the seabed where methane hydrate exists.The, methane hydrate was produced in the sand specimen set in the triaxial cell to measure its shear strength. Moreover, methane hydrate formation was replicated and methane hydrate was dissociated under different conditions of temperature and pressure in order to understand the resulting deformation behavior of the ground.On the basis of experimental results, an elastoplastic constitutive model for methane hydrate-bearing sand was developed based on subloading surface model. The bonding effect due to the cementation by methane hydrate was introduced into the model The bonding force was correlated with the pressure and temperature according to the experimental results. The simulation performed on the triaxial behaviour of methane hydrate-supported sand under various pressure and temperature condition showed good agreement with the experimental results.