含水合物细粒土的强度和变形特性

天然气水合物是一种巨大能源,深刻刻画水合物储层的力学性质是安全开采气体的重要前提。目前对含水合物沉积物力学特性的研究主要针对粗粒土,而对于细颗粒沉积物研究较少。然而,中国南海神狐海域水合物储层区的沉积物是泥质粉细砂型。基于此,参照神狐海域水合物赋存区沉积物的物理性质配制了试验土样,形成了含四氢呋喃(THF)水合物细粒土,对其进行了三轴剪切试验。结果显示:在低围压和高水合物饱和度下,含水合物细粒土试样的应力应变曲线呈现应变软化,而在高围压和低水合物饱和度下表现为应变硬化;含水合物细粒土随剪切作用表现出剪缩效应;强度和刚度随着水合物含量和围压增加而提高;水合物含量的增加明显提高了黏聚力,但是对内摩擦角的影响很小。基于摩尔库伦强度准则,建立了破坏强度与围压和水合物饱和度间的关系,该关系式可以较好地预测强度的变化。

Strength and Deformation Properties of Hydrate-bearing Fine-grained Soil

Natural gas hydrate is a huge energy source, and profoundly describing the mechanical properties of hydrate reservoirs is an important prerequisite for safe gas exploitation. At present, the research on the mechanical properties of hydrate-bearing sediments mainly focuses on coarse-grained soils, while there are few studies on fine-grained sediments. However, the sediments in the hydrate reservoir area in the Shenhu area of the South China Sea are argillaceous silt fine sand. Based on this, the test soil samples were prepared according to the physical properties of the sediments in the hydrate occurrence area of the Shenhu sea area, and the fine-grained soil containing tetrahydrofuran (THF) hydrate was formed, which was subjected to a triaxial shear test. The results show that under low confining pressure and high hydrate saturation, the stress-strain curve of the hydrate fine-grained soil sample shows strain softening, while under high confining pressure and low hydrate saturation, it shows strain hardening. The fine-grained soil exhibits a shear shrinkage effect with shear; the strength and stiffness increase with the increase of hydrate content and confining pressure; the increase of hydrate content significantly increases the cohesion, but has little effect on the angle of internal friction. Based on the Mohr-Coulomb strength criterion, a model for the relationship between failure strength and confining pressure and saturation was established, which can predict the change of strength better.