关键词: 天然气水合物, 粉质沉积物, 水饱和状态, 三轴剪切试验, 强度, 变形特性, 黏聚力

Abstract: This paper aims to investigate the mechanical behaviors of natural gas hydrate-bearing silty sediments, which provides an important basis for the production of abundant natural gas hydrate resources deposited in silty reservoirs of the South China Sea. Thus, silty sediments were artificially prepared according to the particle size distribution curve of hydrate cores from the South China Sea; the natural gas hydrate-bearing saturated silty sediments were simulated based on the "hydrate formation water saturation isotropic consolidation" method, followed by a series of triaxial drained shear tests under low effective confining pressure. The study reveals that:(1) at a low effective confining pressure, the failure strength of silty sediments increases almost linearly with the increasing hydrate saturation, while for the sediments containing hydrates of the same saturation, the failure strength under water saturation is significantly lower than that under gas saturation; (2) the natural gas hydrate with a saturation of 40 % contributes to an increase by about 4 times in the cohesion of silty sediments and by about 5.2° in the internal friction angle; (3) as the effective confining pressure increases, the volumetric strain of silty sediments containing hydrates increases at first and then decreases, whereas that of pure silty sediments decreases continuously; the volumetric strain of all silty sediments decreases with increasing hydrate saturation, and the difference in volumetric strain gradually decreases; (4) the hydrate cementation can reduce the initial consolidation degree of silty sediments, while the shearing deformation behaviors of sediments are mainly influenced by the combination of initial consolidation degree, hydrate cementation and effective stress. The conclusion indicates that the cohesion reduction, re-consolidation and shear deformation as result of the decreased hydrate saturation may be the key reason for the deformation of silty reservoirs induced by natural gas hydrates production in the South China Sea.

Key words: natural gas hydrate, silty sediments, water-saturated state, triaxial shear test, strength, deformation behaviors, cohesion