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高校地质学报 ›› 2022, Vol. 28 ›› Issue (5): 747-757.DOI: 10.16108/j.issn1006-7493.2022043

• 南海海洋地质、构造与油气资源专辑 • 上一篇    下一篇

考虑天然气水合物上覆层不排水抗剪强度深度变化的海底斜坡稳定性影响分析

王 辉1, 2,修宗祥2,孙永福2, 3*,刘绍文1,宋玉鹏2,董立峰2,宋丙辉2   

  1. 1. 南京大学 地理与海洋科学学院,南京 210023;
    2. 自然资源部 第一海洋研究所,青岛 266061;
    3. 青岛海洋科学与技术国家实验室 海洋地质过程与环境功能实验室,青岛 266061
  • 出版日期:2022-10-20 发布日期:2022-10-20

Analysis of the Stability of Submarine Slope Considering the Effects of Undrained Shear Strength of the Cover Layer of Gas Hydrates

WANG Hui1,2,XIU Zongxiang2,SUN Yongfu2,3*,LIU Shaowen1,SONG Yupeng2,DONG Lifeng2,SONG Binhui2#br#   

  1. 1. School of Geography and Ocean science, Nanjing University, Nanjing 210023, China;
    2. The First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China;
    3. Laboratory for Marine Geology and Environment, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China
  • Online:2022-10-20 Published:2022-10-20

摘要: 天然气水合物分解可以诱发海底斜坡失稳对海底工程设施产生造成破坏影响。因此,海底斜坡稳定性状态评价对海底工程设施选址、安全运行具有重要意义。文章根据南海北部神狐海域水合物富集区工程地质特征,采用有限元强度折减法分析了斜坡几何参数、土层强度变化,以及水合物储层特征等因素对水合物分解前后海底斜坡稳定性的影响规律。结果表明,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,水合物层强度降低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。

关键词: 天然气水合物, 稳定性, 海底滑坡, 强度折减, 神狐海域

Abstract: The decomposition of natural gas hydrates can induce the instability of submarine slopes and damages to submarine engineering infrastructures. Accordingly the stability assessment of the submarine slope is of great significance to the site selection and safe operation of the submarine engineering infrastructures. Based on the engineering geological characteristics of the hydrate-enriched area in the Shenhu offshore area in the northern South China Sea, we use the finite element strength reduction method to analyze the effects of the slope geometry, soil strength changes, and hydrate reservoir characteristics on the stability of the submarine slope before and after hydrate decomposition. The results show that, without the consideration of the hydrate decomposition, the stability of the submarine slope is mainly controlled by the slope of the slope gradient and the soil strength, and it is mainly manifested as a shallow landslide. However, when the decomposition of hydrate is considered, the reduction in the strength of the hydrate-bearing layer will affect the overall stability of the slope, but the position of the most dangerous sliding surface under the same overburden condition is greatly affected by the depth of the hydrate-bearing layer. A critical burial depth that is controlled by the terrain geometry and the strength of the overlying soil exists. In addition, when the burial depth is greater than the critical burial depth, the hydrate decomposition has little effect on the stability of the slope, and the most dangerous sliding surface is located in the upper shallow layer, which manifests as a shallow surface failure. When the burial depth is less than the critical burial depth, the most dangerous sliding surface passes through the hydrate-bearing layer, which shows a deep landslide. Finally, according to the buried depth conditions of the hydrate-bearing layer in our current model, the safety factor of the deep sliding surface after hydrate decomposition is still larger than that of the shallow layer, indicating the submarine landslide hazards in this area are mainly shallow landslides.

Key words: gas hydrate, stability, submarine landslide, strength reduction, Shenhu offshore area

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