In the recent activities of off-shore drillings conducted in Tokai-oki and Kumano-nada off the coast of Japan, MH21 research consortium of Japan confirmed methane hydrate in sandy and/or mud-sand alternation layers. Dissociation of methane hydrate existing in pore of marine sediments in deep water may result in strata deformation surrounding possible production wells in the future. A specially designed pressure vessel was used to clarify compaction behavior of methane hydrate bearing sediment during the dissociation of methane hydrate. In the study, methane hydrate was formed artificially in Toyoura sand which was densely compacted in the vessel, and compaction behavior on hydrate dissociation was monitored along with the measurements of vertical displacement, temperature and pore pressure. It was found that the displacement of Toyoura sand during hydrate dissociation approached finally to that of plain Toyoura sand. The experimental results imply that the final deformation is mainly caused by the depressurizing performance for methane hydrate dissociation.
Drilling survey for methane hydrate in the region of Kumano-nada to Tokai-oki has brought a prospective evidence of hydrate reservoir under the deep seafloor off the coast of Japan. MH21 research consortium of Japan has been developing a production simulator or a hydrate reservoir simulator from the beginning of the MH21 project. Our research group is providing a consolidation calculation module for the production simulator. Meanwhile, there is not much information on compaction behavior of sand reservoir during dissociation of methane hydrate. It is still difficult to have better understanding of real phenomena during dissociation of methane hydrate in production. Especially, mutual relationships among pore pressure, temperature and deformation in hydrate bearing sediment. Experimental achievement has not been made so far over strata deformation with regard to hydrate dissociation in sediment strata.
