Effects of hydrate occurring mechanisms and saturation on the mechanical properties of hydrate-bearing sediments: Numerical study based on simplified DEM simulation

Abstract

Natural gas hydrate is a strategic alternative energy source which are widely founded in seabed sediments. The study of the mechanical properties of hydrate-bearing sediments is the key content to ensure the safe exploitation of gas hydrate. Hydrate occurring mechanisms and saturation are important factors affecting the mechanical properties of hydrate-bearing sediments. In this work, simplified discrete element models that consider the hydrate occurring mechanism, hydrate saturation and confining pressure, were generated based on PFC code. Three main hydrate occurring mechanisms including pore filling, load bearing and cementation were characterized. The triaxial compression simulation was then conducted to investigate the model mechanical properties. The results show that the hydrate of cementation mode has the most obvious strength-enhancing effect on sediments, followed by the load bearing model and pore filling model. Hydrate occurring mechanism also affect the increasing trend of sediment strength and deformation modulus with hydrate saturation and confining pressure. The influence of hydrate occurrence mechanism on the mechanical behavior of sediment is largely controlled by the interaction between hydrate and sand particles interface. The hydrate of cementation mode increases the cohesion of the sediment particles, the hydrate of pore filling mode increases the friction between particles, and the hydrate of load bearing mode has the combined effects of the above two.