气饱和含CO_2水合物砂的三轴压缩试验

Triaxial compression tests on gas saturated CO_2-hydrate-bearing sand

在改造的高压低温三轴仪中采用过量气法制备了气饱和状态的含CO_2水合物砂样,并进行了三轴压缩试验。以水合物饱和度为指标对过量气制样法的可重复性进行分析后发现,受孔隙阻隔效应的影响,虽然利用高的初始水饱和度的砂样可以制成高的水合物饱和度的含水合物砂,但是制样的可重复性低;试验表明,采用过量气法制取水合物饱和度低于40%的含水合物试样的可重复性较好。三轴试验结果表明,含水合物砂的剪切和变形特性与水合物饱和度和净围压密切相关:随净围压的增大,试样的强度、刚度、塑性和压缩性都增大,随水合物饱和度的增加,试样的强度和刚度增加,塑性和压缩性降低;黏聚力随水合物饱和度的增加而增加,但摩擦角并没有明显的变化。

To improve the understanding of the mechanical behavior of the gas-hydrate bearing sediments, a series of triaxial compression texts was performed on gas saturated CO_2-hydrate-bearing sand. Samples were prepared using the excess gas method, in a modified high-pressure low-temperature triaxial apparatus. The hydrate saturation could be determined readily according to the gas assumption. The repeatability of sample making was analyzed in terms of the hydrate saturation. It was found that samples with high hydrate saturation could be formed from samples with high initial water saturation, however, the repeatability of making samples, which was affected by pore blocking effect, was low. It was shown that the repeatability of making samples with hydrate saturation lower than 40% using the excess gas method was relatively good. The triaxial test results show that the mechanical behavior of hydrate-bearing sand samples depends largely upon the hydrate saturation and the applied net confining pressure. The strength, stiffness, ductility and compressibility of hydrate bearing specimens increase with the effective confining pressure; as hydrate saturation increases, the strength and stiffness of specimens increase, while the ductility and compressibility decrease. In addition, the larger the hydrate saturation, the larger the apparent cohesion, whereas the friction angle remains practically unchanged.