BASIC RESEARCH ON THE MECHANICAL BEHAVIOR OF METHANE HYDRATE-SEDIMENTS MIXTURE

The possible existence of a vast amount of methane hydrate around islands has attracted attention as the largest potential hydrocarbon resource in Japan. At the same time, several production methods have been considered to extract the gas from the hydrate zone. Although it is known that the hydrates pose significant obstacles to drilling and production operations, there is at present only limited knowledge on the mechanical behavior of hydrate-rich zones, which is necessary to understand the stability around the site. In order to know the properties of methane hydrate and/or its sand mixtures, a series of tests was carried out on artificial methane hydrate-sand mixtures, using low temperature and a newly developed high confining pressure triaxial compression technique. The sediments used in the mixture were obtained from a 207.75m sea bottom core from the Nankai Trough, located 1152.75m below sea level. The specimens used were prepared by compressing a mixture of artificial methane hydrate and the sediments with a volume ratio of sediments to the whole of specimen. On the basis of these experimental results, the factors affecting mechanical properties of the hydrate and sediment mixtures are discussed. It is very essential to collect more data on the properties of methane hydrate and/or sedimentation (soil) mixture to understand the stability of any attempt at methane hydrate production.