Interfacial strength between ice and sediment: A solution towards fracture-filling hydrate system

Fracture-filling natural gas hydrates (NGH) are widely distributed in marine shallow clayey-silt sediment, and usually develop in forms of nodular, veins, layers, and massive pure hydrate. Interactions between these hydrate individuals and their surrounding sediment are crucial to evaluate potential submarine geohazards related to fracture-filling NGH systems. In this paper, we develop a novel apparatus to detect interfacial strength between hydrate individual and its host sediment. Shear strengths of three typical substances (i.e., massive pure hydrate, hydrate-saturated sediment, and hydrate-to-sediment interfaces) in fracture-filling NGH systems are examined and compared comprehensively by taking ice as substitute. Possible failure patterns of the fracture-filling NGH systems are discussed, and a tree-like model is proposed to describe formation mode and failure patterns of the fracture-filling NGH reservoirs. The results indicate that the load-displacement curves and shear surface characteristics of the ice-sediment interface differs significantly from those of the pure ice and ice-bearing sediment. The load-displacement curves of the ice -sediment interfacial specimens show double-peak loading characteristics, with multiple interlaced cracks on the shear surface. Additionally, the strength of the ice -sediment interfacial specimens is sensitive to shear rate, and decreases with increasing shear rate. These double-peak failure behaviors and rambling cracks in the shear surface are attributed to the nonlinear contact interfaces and two transitional sub-systems (i.e., silt-bearing ice and ice-bearing silt) in the specimens.