Abstract: The hydrate formation in porous media below freezing point is a complicated multiphase transition process, including water, ice, hydrate and bound water. In order to study the formation behaviors of methane hydrate in porous media below freezing point, such as water conversion, gas consumption and stable conditions, the formation experiments of methane hydrate in porous media were carried out. The silica gels with the mean pore diameters of 1295 nm, 1796 nm and 3320 nm were used as the porous media for the experiments. The experimental results indicate that the water conversion in the porous media after the hydrate formation increases with the increase of the initial formation pressure, the decrease of the bath temperature and the increase of the mean pore diameter. The particle size of the porous media reduces the formation rate of the hydrate but has a slight effect on the final gas consumption. At the same experimental temperature, the system pressure after the hydrate formation, the final gas consumption and the final water conversion increase with the increase of the initial formation pressure. The differences of final system pressure and water conversion in the different initial pressure experiments increase with the formation temperature. Due to the effect of the capillary force and the bound water in porous media, the water conversion of the hydrate formation significantly becomes lower. At the experimental conditions in this study, the highest water conversion is up to 32.39%.

Key words: methane hydrate, formation behavior, below freezing point, porous medium, pore diameter, conversion