冷泉形成的数值模拟研究  

Numerical simulation on the formation of cold seepage

作　　者：刘善琪[1] 尹凤玲[1] 朱伯靖[1] 李永兵[1] 石耀霖[1] 

机构地区：[1]中国科学院计算地球动力学重点实验室,中国科学院大学,北京100049

出　　处：《地球物理学报》2015年第5期1731-1741,共11页Chinese Journal of Geophysics

基　　金：国家自然科学基金(NSFC41174067);中国科学院国际合作创新团队项目(KZZD-EW-TZ-19)资助

摘　　要：海底冷泉形成的一种可能机制是海平面下降引起天然气水合物的分解.本文基于对冷泉渗漏特征的分析,建立了二维轴对称模型,利用有限元方法定量分析了南海区域海平面下降对冷泉形成的影响.结果表明,末次冰盛期（26.5～19.0ka BP）海平面下降引起的冷泉活动可以持续到现在,但是从水合物停止分解至今,超孔隙压力的极值在持续减小,而流体向海底的渗漏达西速度先快速减小、然后缓慢减小.同时发现,流体向海底的渗漏达西速度与管状通道的渗透率、通道周围介质的渗透率以及通道的半径等有关,估计目前的冷泉活动还可以持续10000年以上.海平面下降引起的天然气水合物分解,可能是影响全球气候变化的一个重要因素.Cold seepage,stemmed from the decomposition of natural gas hydrate below the seafloor and controlled by the seawater pressure gradient,is mainly composed of water,hydrocarbons,hydrogen sulfide or carbon dioxide,and its temperature is similar to sea water.As an important prospecting area for hydrate resource in South China Sea,aplurality of cold seepage areas have been found in recent years,but it seems still unclear such as the exact time,dimensions,trigger mechanism of gas hydrates decomposition,and its relevance to climate change and sea level change in most parts of the South China Sea.In order to quantitatively study the effect of sea-level falling on the formation of cold seepage,the dynamic finite element model of hydrate decomposition was established based on the analysis of the characteristic of cold seepage to simulate the seepage Darcy velocity on different permeability conditions and the changes of excess pore pressure caused by hydrate decomposition with time.Firstly,calculate uplifting height of the base of gas hydrate stability zone（BGHS）based on the falling height of sea level,the natural gas hydrate phase equilibrium equation,the hydrostatic pressure formula,the temperature-depth equation of seafloor and the temperature-depth equation of deposition layer. Then establish two-dimensional axisymmetric model according to the characteristic of cold seepage,and set its material properties according to the previous studies onthe composition of seafloor sediments and the properties of methane hydrate,methane,and sea water.The timeframe for this study is set as 26500 years,starting from the beginning of the Last Glacial Maximum（26.5ka BP）,and the hydrate decomposition time is set as 7500 years.The computational time step is set as 100 years.The excess pore pressure of upper boundary and lower boundary is set as zero,the right boundary set as impervious,and the left boundary is set as symmetric.Use structured quadrilateral mesh generation method to divide the model,and refine the mesh of hydrate zon

关 键 词：天然气水合物 冷泉 有限元 海平面下降 

分 类 号：P542[天文地球—构造地质学]