Effect of Hydrate Distribution on the Mechanical Response of Hydrate-Bearing Sand: Discrete Element Method Simulation

Natural gas hydrates are cage-like crystalline solids that are globally recognized as a potential energy suitable for sustainable development. Hydrate distribution often affects the mechanical properties of hydrate-bearing sediments. The objective of this work is to investigate the underlying strengthening mechanisms of hydrate-bearing sediments under different hydrate distributions. The discrete element method is used to prepare numerical hydrate-bearing sediments and simulate biaxial compression tests. Hydrates are simulated as small cemented particles that are either randomly distributed or gathered filling the hydrate-free sediments. The simulation results show that at hydrate saturation of 45%, the sediment with randomly distributed hydrates exhibits higher peak strength, strain-softening and a run-through shear band, while the sediment with gathered hydrates shows higher residual strength and a cross-type shear band. Micromechanical exploration finds that many hydrate-related micro force chains are created to share the load component. In the sediment with a randomly distributed hydrate, a more stable force chain complex is formed, which is subjected to a smaller force concentration, improving the strength and stability of the sediment. As the hydrate particles gather in the sediment, the bonding forces become more concentrated and the hydrate can participate in the skeleton that contributes to the residual strength of the sediment.