A particle-scale study of the triaxial compression behavior of methane hydrate-bearing sands

Macroscopic geomechanical properties of methane hydrate-bearing sands (MHBSs) have attracted much scholarly attention. But the associated particle-level mechanisms often rely on assumptions. In this paper, triaxial compression tests and numerical simulations using discrete element method (DEM) are combined to study the unique mechanical properties of MHBS at the particle scale. The triaxial compression tests understand the basic mechanical properties of MHBS, and the experiments results are used for DEM modeling and parameter calibration. Small cementing particles are used to simulate methane hydrate, showing dispersion and coalescence distributions in sediments to simulate different hydrate spatial distributions. The simulation results show that in MHBS samples, the increasing hydrate saturation enhances the cementation network as well as the hydrate-related micro-force chains, and the particles in the cementation network jointly share the loading. The hydrate cementation is restricted by the high effective confining pressure as the cementation network was subjected to an ultimate strength. For hydrate cementation failure, the high effective confining pressure increases the proportion of shear breakage, but tensile breakage is the dominant failure form. The sample with hydrate coalescence distribution behaves strain hardening, while the sample with hydrate dispersion distribution yields later and shows strain softening with a higher peak strength. Finally, the stress-induced anisotropy in microstructure fabrics is observed, and the development of radial fabrics is hindered by hydrates, especially the coalesced hydrates.