Discrete Element Analysis of One-Dimensional Dissociation of Hydrates in Methane Hydrate-Bearing Silt

The macro and microscopic properties of methane hydrate-bearing soils（MHBS）subjected to hydrate dissociation control the reservoir stability in methane hydrate exploration engineering. By randomly filling hydrate particles into the silty skeleton and installing bond contact model at silt-hydrate and hydrate-hydrate contacts, a discrete element model for MHBS was established. In the DEM model, van der Waals forces between fine particles and the effect of temperature-back pressure condition on the bond strength are considered. Considering the influence of temperature-back pressure parameter on the rate of hydrate dissociation. Simulation of hydrate dissociation using depressurization under one-dimensional stress condition is carried out. The results show that: The skeleton void ratio gradually decreases while the deviator strain gradually increases under hydrate dissociation, with some deformation recovered in the stress recovery stage. In terms of fabric, the degree of anisotropy of the contact normal of silt-silt contacts gradually decreases while those of silt-hydrate and hydrate-hydrate contacts increase throughout hydrate dissociation. In terms of stress-bearing, the hydrate is efficient to bear the mean stress rather than the deviator stress. When the hydrate saturation degree decreases to 4%~6%, the hydrate bearing ratio on the mean stress is about 16%, while the hydrate bearing ratio on the deviator stress is about 1%, indicating different effects of hydrate dissociation on the soil shear strength and the soil volumetric yielding.