A cohesionless micromechanical model for gas hydrate-bearing sediments

Proper representation and understanding of the mechanical response of the sediment is a prerequisite for successful future gas production from gas hydrate-bearing sediments, in view of the geotechnical issues encountered in recent field trials. Recent investigations have indicated that the increase of sediment strength, due to hydrate existence, is of frictional nature and associated with changes in the kinematic response, and not necessarily due to cementation. Following this idea, this paper presents a non-cohesive micro model for methane-hydrate-bearing sediments, where the hydrate is represented as solid particles precisely positioned between sand particles, contributing to the skeleton response even for small strains. Analytical expressions relating between the geometry, inter-particle properties, and the mechanical response of the hydrate-bearing sediment are developed in the paper. Global stress-strain response is evaluated under simulated triaxial loading, exhibiting stiffer, stronger and more dilative response compared to pure sand samples. It is shown that a trade-off exists between the particle size and the inter-particle friction, which can be unified using a participation factor related to the pore size distribution. As observed in recent experimental investigations, the suggested model results in a cohesionless response when analyzed using Rowe's stress dilatancy theory.