Integrated core-log facies analysis and depositional model of the gas hydrate-bearing sediments in the northeastern continental slope, South China Sea
Integrated core-log facies analysis and depositional model of the gas hydrate-bearing sediments in the northeastern continental slope, South China Sea
复制标题
南海东北部陆坡含天然气水合物沉积物岩心-测井相综合分析及沉积模式
DOI：
10.1016/j.marpetgeo.2017.07.012
复制
发表时间：
2017
影响因子：
4.2
通讯作者：
Lin Lin
中科院分区：
文献类型：
--
作者：
Zhong Guangfa;Liang Jinqiang;Guo Yiqun;Kuang Zenggui;Su Pibo;Lin Lin
赋矿沉积物对天然气水合物成藏有重要影响。然而，这个问题在文献中基本上被忽视了。结合岩心观察和随钻测井资料，研究了南海东北缘含细粒天然气水合物沉积物的类型、特征和沉积模式。含天然气水合物的沉积物主要为形成于上陆坡峡谷间脊的泥质沉积物，包括半长岩、碎屑岩（含角砾岩的泥质）和细粒浊积岩。冷泉碳酸盐岩和相关的滑塌堆积物、泥质角砾岩碎屑岩以及粗粒浊积岩可能局部出现。通过聚类分析，将测井相划分为4类6亚类。岩心-测井对比表明，天然气水合物主要分布在高电阻率、低声波时差（AC）测井响应的细粒沉积物中，与高自然伽马（GR）、高AC、低电阻率的细粒背景沉积物和低GR、高电阻率、高密度、低AC、低孔隙度的渗漏碳酸盐岩很容易区分。主要的寄主沉积物由细颗粒的半远洋沉积物组成，这些沉积物是由河流物质的云状层和海水柱中的微体化石沉积而成的。然而，大多数半远洋沉积物可能已被滑塌和相关的重力流过程广泛修改，并以碎屑和浊积岩的形式重新沉积。与天然气水合物分解和渗漏有关的当地开发的渗漏碳酸盐为重力流沉积物提供了额外的来源。
Host sediments may exert a significant influence on the formation of gas hydrate reservoirs. However, this issue has been largely neglected in the literature. In this study, we investigated the types, characteristics and the depositional model of the fine-grained gas hydrate-bearing sediments in the northeastern margin of the South China Sea by integrating core visual observations and logging-while-drilling downhole logs. The gas hydrate-bearing sediments consist dominantly of muddy sediments formed in the inter-canyon ridges of the upper continental slope, including hemipelagites, debrites (mud with breccia) and fine-grained turbidites. Cold-seep carbonates and associated slumping talus, muddy breccia debrites, as well as coarse-grained turbidites, may locally occur. Four classes and six sub-classes of log facies were defined by cluster analysis. Core-log correlation indicates that gas hydrates are majorly distributed in fine-grained sediments with high resistivity and low acoustic transit time (AC) log responses, which are easily differentiated from the fine-grained background sediments of high gamma-ray (GR), high AC, and low resistivity log values, and the seep carbonates characterized by low GR, high resistivity, high density, low AC and low porosity log values. The primary host sediments consist of fine-grained hemipelagic sediments formed by deposition from the nepheloid layers of river material and from the microfossils in seawater column. Most of the hemipelagic sediments, however, might have been extensively modified by slumping and associated gravity flow processes and were re-deposited in the forms of debrites and turbidites. Locally developed seep carbonates associated with gas hydrate dissociation and leakage provided additional sources for the gravity flow sediments.