INFLUENCE FACTORS AND RISK ASSESSMENT FOR SEABED LANDSLIDES INDUCED BY NATURAL GAS HYDRATE DECOMPOSITION
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摘要:
天然气水合物主要赋存于低温高压下的海底沉积物层中，当周围环境的温度或者压力发生变化时，其稳定性会受到破坏，诱发坍塌、海底滑坡等地质灾害，对钻井平台、海底电缆等造成巨大破坏。结合南海北部海底陆坡的实际地震资料，首先获得了符合实际情况的储层属性参数，然后基于改进的地质力学模型，获得了相应的力学模型参数，利用孔隙压力平衡方程计算得到地层的有效应力，对天然气水合物分解诱因的海底滑坡的数值模拟，基于强度折减法讨论分析了初始水合物分解量、水合物分解总量等因素引起的水合物储层变化的力学响应，获得了对应的安全系数，实现了水合物分解对海底边坡稳定性影响的分析，为今后水合物开采过程中可能诱发边坡失稳的程度及失稳位置分布预测提供了指导和帮助。
Abstract:Natural gas hydrate mainly occurs in the seabed sediments under low temperature and high pressure. When temperature or pressure changes, the stability of gas hydrate will be damaged, and geological disasters, such as submarine landslide and sediment collapse triggered, which will cause severe damage to offshore platforms and submarine cables. In this paper, based on the seismic data acquired from the submarine continental slope in northern South China Sea, actual reservoir property parameters and corresponding mechanical model parameters are acquired with the improved geomechanical model. Effective formation stress is calculated with the equilibrium equation of pore pressure. Upon the basis, the numerical simulation of submarine landslide induced by the decomposition of natural gas hydrate is made. Then, using the strength reduction method, the mechanical response of hydrate reservoir change caused by initial hydrate decomposition amount and total hydrate decomposition amount is calculated. Upon the correspondent safety factor distribution diagrams, we made a preliminary analysis of undersea landslide caused by hydrate decomposition. The results provide a guidance for prevention of primary or secondary environmental geohazards in the future exploitation of gas hydrate.
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表 1 模型抗剪参数
Table 1. Model shear resistance parameters
内聚力/Pa 内摩擦角/（°） 剪胀角/（°） 抗拉系数 黏土层 25 000 16 8 1.0×1010 水合物层 10 000 18 9 1.0×1010 粉砂质泥岩 25 000 25 12.5 1.0×1010 砂岩 25 000 25 12.5 1.0×1010 
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