南海北部陆坡水合物分解引起海底不稳定性的定量分析

A quantitative analysis for submarine slope instability of the northern South China Sea due to gas hydrate dissociation

分析了天然气水合物分解引起海底斜坡不稳定性的原因,探讨了水合物分解引起沉积物层孔隙压力变化规律.以南海北部神狐海域水合物样品钻获区为研究对象,应用极限平衡法探讨了海底无限斜坡的稳定性问题,计算了设定的不同滑动面的安全系数,建立了目标不稳定区相关参数条件下的水合物分解与海底斜坡不稳定的模式图,模拟计算了不同程度的水合物分解对海底斜坡失稳的影响作用.结果表明:在假设条件下,南海神狐海域当水深为1200m,沉积物层厚度为200 m,对于20°的较大坡角,沉积物层中5%水合物分解将引起海底斜坡失稳;斜坡坡角为5°时,沉积物层中15%水合物分解后,将会引起海底斜坡失稳;当斜坡坡角为3°或更小时,沉积物层中25%水合物分解后,将会引起海底斜坡失稳.

This paper analyzed the factors of instability of submarine slope, and discussed the pore pressure change of submarine sediments in the northern South China Sea due to gas hydrate dissociation. We select the Shenhu area of the northern South China Sea as the study case，made a quantitative assessment of the stability of submarine infinite slope by utilizing limiting equilibrium theory, and acquired the safety factors of different landslide planes assumed beforehand, numerically simulated the effect of gas hydrate dissociation on stability of submarine slope. The results of the study showed that 15% gas hydrate dissociation will lead to submarine slope failure under the condition of water depth 1200 m, sediments depth 200 m, and slope angle 5°. Under the same condition of water depth and sediments depth, more percentage of gas hydrate dissociation is needed for submarine slope failure for smaller slope angle. For bigger slope angle such as 20°, only 5% gas hydrate dissociation will lead to submarine slope failure.