A numerical investigation on the mechanical properties of hydrate-bearing sand using Distinct Element Method

Abstract

Natural gas hydrates (NGH) are cage-like crystalline solids that are widely found in marine and permafrost sediments. The microstructure of NGH affects the mechanical properties of hydrate-bearing sediments (HBS). However, the underlying mechanisms are often difficult to detect. In this paper, Distinct Element Method (DEM) is used to simulate the microstructure of hydrate observed in CT slices. Biaxial compression tests are conducted to investigate the mechanical properties of HBS and the relevant strengthening and volumetric dilation mechanisms. The simulation results show that the hydrate and sand particles jointly share the loading and many hydrate-related micro force-chains are created. Hydrate enhances the cohesive strength and frictional strength components of HBS. Compared with hydrate free sediment, the internal friction angle of the sediment at 45% hydrate saturation increases by 2.38°, but hardly increases for the sediments at 5% and 20% hydrate saturations. Large local porosity changes and intensive hydrate cementation failure occur in the regions where the shear bands develop. Particle-scale observation shows the deformation characteristics of hydrate and the effects of hydrate on the structure and strength evolution of HBS.