We conducted an experimental study on the dissociation of methane hydrate (MH) and gas production behavior by depressurization in sediments. To reproduce the actual flow condition of gas and water, disc-shaped samples of MH in sediments were used. Horizontal radial flow in porous media during MH dissociation was studied under a variety of vertical loads in order to reproduce field conditions in real MH sediments. From experimental observations, it was found that the MH dissociation consisted of 2 stages due to the latent heat of sediments and thermal conduction. Based on experimental results, we carried out numerical simulations of laboratory-scale experiments for depressurization. Thermal conductivity that dominated dissociation behavior was optimized. Further, we formulated realistic relative permeability curves that allowed us to reproduce the gas-water production behavior under the existence of MH.
Methane hydrate (MH) existing in marine sediments close to Japan is expected to be developed as an alternative energy resource to oil and coal (Okuda, 1993; Sato et al., 2001a, b). To develop this domestic resource in the future, the Agency for Natural Resources and Energy(ANRE) under the Ministry of Economy, Trade and Industry (METI) formulated Japan's Methane Hydrate Exploitation Program in 2001 and established the Research Consortium for Methane Hydrate Resources in Japan (MH21) consisting of the following 3 divisions: Resources Assessment, Production Method and Modeling, and Environment Impact (METI, 2001). This project is based on the mid- and long term program aimed at the commercial production of methane gas from an MH reservoir in 2016. In 2003, the preliminary drilling Tokaioki-Kumanonada was carried out, and the existence of a zone containing a large amount of MH was confirmed in the east Nankai trough area.