ABSTRACT:

With an integrated apparatus for hydrate-bearing sediment (HBS) syntheses and tri-axial test, a series of shear tests on the static and dynamic properties of the methane and THF hydrate-bearing sediment consisted with fine silty sand were carried out. The stress-strain and shear strength characteristics were analyzed. The development of the pore pressure and the remaining strength of the HBS and the saturated fine silty sand under cyclic loads after the dissociation of hydrate were investigated. It was shown that the HBS behaved as plastic failure. The larger the confined pressure was, the higher the strength was.

INTRODUCTION

Natural gas hydrate, a crystalline solid composed mainly of methane gas molecules and water molecules, is stable in high pressure and low temperature conditions. In nature, gas hydrate is distributed extensively in ocean sediments, continental margins and deep lakes and is regarded as a kind of potential energy resource (Winters et al., 2007). In recent years, methane hydrate (MH) have attracted great interest from the scientific communities (Clayton et al., 2005; Sloan, 1998). A common interest concerned with submarine MH is the need to identify their global and local occurrence, concentration and form, and methods for exploitation. Since MH exists only under very restricted conditions, it is difficult to determine their presence and properties by drilling, or to bring undisturbed specimens to laboratory for testing. A more promising method of locating and characterizing hydrates comes from the development of marine seismic geophysical testing. However, the development, validation, and optimization of seismic surveying techniques require an understanding of the relation between the sediment type, hydrate form, content, physical and mechanical properties of the sediment. Properties of the porous host sediment affect the morphology and the extent of hydrate growth, which in turn alters the host sediment properties (Lee, Collett, 2001).

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