Formation, growth and ageing of clathrate hydrate crystals in a porous medium

Abstract

An experimental study was performed to visually observe the driving force dependence of hydrate growth in a porous medium filled with either liquid water and dissolved CO₂ or liquid water and gaseous CO₂. The given system subcooling, ΔT _sub, i.e. the deficiency of the system temperature from the triple CO₂−hydrate−water equilibrium temperature under a given pressure, ranged from 1.7 K to 7.3 K. The fine dendrites initially formed at ΔT _sub = 7.3 K changed quickly into particulate crystals. For ΔT _sub = 1.7 K, faceted hydrate crystals grew and the subsequent morphological change was hardly identified for an eight-day observation period. These results indicate that the physical bonding between hydrate crystals and skeletal materials becomes stronger with decreasing driving force, suggesting that the fluid dynamic and mechanical properties of hydrate-bearing sediments vary depending on the hydrate crystal growth process.

Acknowledgements

This work was financially supported by the Research Consortium for Methane Hydrate Resources in Japan (MH21) and the National Methane Hydrate exploitation program planned by Ministry of Economy Trade and Industry (METI) and by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (Grant 16-2627). We would like to thank Katsunori Matsushita (Hokkaido Branch, Suzuki Shoko Co., Sapporo Japan), Junji Ito (Ito Keiki Kogyosho, Co., Sapporo), and Shinya Ito (National Institute of Advanced Industrial Science and Technology, Sapporo) for their help in maintaining the apparatus and in the experimental work. One of the authors (D. Katsuki) would like to thank the Japan Society for the Promotion of Science for providing a postdoctoral fellowship.