【作者】 王辉；

【导师】 孙永福； 刘绍文；

【作者基本信息】 南京大学 ， 海洋地质， 2021， 硕士

【摘要】 水合物分解可以诱发海底斜坡失稳并对海底工程设施产生造成破坏,含天然气水合物地层的不稳定性是触发深水工程灾害的潜在条件之一。考虑水合物分解的海底斜坡稳定性的评价是海洋地质灾害研究重要问题。目前关于海底斜坡稳定性分析的研究多是将水合物分解导致的储层强度弱化和土层强度分布不均两种影响因素分开考虑,且对水合物富集区潜在海底滑坡致灾范围的研究较少。本文根据南海北部神狐海域水合物富集区工程地质特征,考虑水合物上覆层不排水抗剪强度沿深度方向的变化,展开含水合物层的海底斜坡稳定性评价并对研究区潜在滑坡进行滑动后预测。主要的研究成果如下:研究区含水合物层的海底斜坡的最危险滑动面主要有两种表现方式,一种位于水合物层上覆层浅部,一种则为过水合物层顶界。未考虑水合物分解时,海底斜坡稳定性主要受控于斜坡坡度和土体强度,且主要表现为浅层滑坡。考虑水合物的分解时,水合物储层强度的弱化导致会对斜坡的整体稳定性产生影响,但同等上覆层条件下,最危险滑动面位置受水合物层埋深影响较大,且存在受地形几何特征与上覆土层强度控制的临界埋深。埋深大于临界埋深时,水合物分解对斜坡稳定性的影响较小,最危险滑动面位置位于上部浅层,表现为浅表层破坏。小于临界埋深时,最危险滑动面位置则经过水合物层,表现为深层滑坡。根据目前模型中的水合物层埋深条件,水合物分解后的深层滑动面安全系数仍高于浅部地层,意味该海域水合物开采仍需要关注浅层海底滑坡灾害的影响。以研究区内某一含水合物储层的实际海底斜坡的声学剖面为例,基于研究区工程地质条件,采用BING软件对计算得到的潜在海底滑坡的运动状态进行模拟。结果表明,重塑状态下的滑坡体相较与初始状态的滑坡体,具有高流速、远滑距和低厚度的特点。含水率一定时,灵敏度越高,滑坡体的初始强度越大,易在地形平坦、低洼处或爬升时会形成较厚的沉积层。含水率越大,滑坡体的流动性增强,端部的运移速度与滑动距离越大,对最大运移速度处的地形改造作用和海底工程设施破坏作用也随之增加。该结果可以为研究区的潜在滑坡的致灾范围预测和灾害防护提供一定的参考。更多还原

【Abstract】 Hydrate decomposition can induce submarine slope instability and damage submarine engineering facilities.The instability of gas-bearing hydrate formation is one of the potential conditions for triggering deep water engineering disaster.The evaluation of slope stability considering hydrate decomposition is an important problem in marine geology disaster research.At present,the research on the stability analysis of submarine slope mainly considers the weakening of reservoir strength caused by hydrate decomposition and the uneven distribution of soil layer strength separately.And there is less research on the potential disaster area of undersea landslide in hydrate rich area.According to the engineering geological characteristics of hydrate rich area in shenhu sea area of the south china sea,this paper takes into account the variation of non-drainage shear strength along the depth of superjacent layer,carries out the stability evaluation of submarine slopes with hydrates layer and makes the prediction of potential landslide after sliding.The main research results are as follows:The most dangerous sliding surfaces of the submarine slopes with hydrate layers in the study area are mainly presented in two ways,one is located at the upper lamination and the other is on the top boundary of hydration layers.When hydrate decomposition is not considered,the stability of the submarine slope is mainly controlled by the slope gradient and soil mass strength,and it mainly manifests as shallow landslide.When considering the decomposition of hydrates,the weakening of the hydrate reservoir leads to an impact on the overall slope stability,however,the position of the most dangerous sliding surface under the same condition is greatly affected by the depth of hydrate layer,and there is a critical depth controlled by topography geometry and overlay strength.Hydrate decomposition has little effect on slope stability when buried depth is greater than critical burial depth.The most dangerous sliding surface is located in the upper shallow stratum,which shows shallow surface failure.Less than the critical burial depth,the most dangerous sliding surface position passes through hydrate layer and manifests as deep landslide.According to the buried depth condition of hydrate layer in the current model,the safety coefficient of deep sliding surface is still higher than that of shallow strata,which means that the impact of the shallow seabed landslide disaster needs to be paid more attentionTaking the acoustic profile of a real submarine slope with hydrate reservoir as an example,BING software is used to simulate the motion state of the calculated potential seabed landslide.The results show that the slip body under remolding has the characteristics of high flow velocity,wide slip distance and low thickness compared with the original slide body.The higher the sensitivity,the greater the initial strength of the landslide,and the thicker the sediments tend to form in flat,low-lying areas or when they climb.The greater the water content,the more fluidity of the landslide,and the larger the velocity and distance between the end and sliding,then the effect of topographic modification and damage of submarine engineering facilities on the maximum velocity of migration will be increased.The results can provide some references for the prediction of potential landslide disaster area and disaster protection in the study area.更多还原