Cheng, YP; Yu, Y; Xu, X; Soga, K; (2014) DEM study on the mechanical behaviours of methane hydrate sediments: hydrate growth patterns and hydrate bonding strength. In: Proceedings of the 8th International Conference on Gas Hydrates (ICGH8-2014). : Beijing, China.

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Abstract

Natural methane hydrate soil sediments attract worldwide interest, as there is huge commercial potential in the immense global deposits of natural gas hydrate that lies under deep seabeds and permafrost regions. However, the geomechanical behaviour of methane hydrate soil is poorly understood. In this study, Discrete Element Method (DEM) was employed to provide insights into the mechanical behaviour of hydrate-bearing sediments with different hydrate patterns in the pores: the pore-filling case and the cementation case. A series of drained triaxial compressional tests were performed, and the results were analyzed in terms of stress-strain response and volumetric response. In both pore-filling and cementation cases, the presence of hydrates caused an increase in the strength and dilative tendency of the simulated hydrate-bearing soil samples, and the strength and dilation both increased with hydrate saturation (or amount of hydrates in the pores). In addition, at the same hydrate saturation, the cementation case showed higher values of strength and dilation than the pore-filling case. In the cementation case, two typical hydrate growth patterns were considered: soil surface coating (hydrates form around the grain surface) and soil-soil contact gathering (hydrates preferentially form at the grain contacts). Results showed that hydrate growth patterns greatly influenced the mechanical behaviour of the simulated hydrate-bearing samples, especially when the bonding strength and hydrate saturation were increased. In both patterns, strength and dilation were enhanced as bonding strength increased, and the enhancement was greater in the soil-soil contact model than in the soil surface gathering model. At high hydrate saturation, as bonding strength increased, a larger axial strain was needed to reach the peak strength, and the development of dilation was delayed.

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