Appearance and preservation of natural gas hydrate from Hydrate Ridge sampled during ODP Leg 204 drilling
Appearance and preservation of natural gas hydrate from Hydrate Ridge sampled during ODP Leg 204 drilling
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DOI：
10.1016/j.margeo.2007.05.003
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发表时间：
2007-10
期刊：
影响因子：
2.9
通讯作者：
G. Bohrmann;W. Kuhs;S. A. Klapp;K. Techmer;H. Klein;M. M. Murshed-M.;F. Abegg
中科院分区：
文献类型：
--
作者：
G. Bohrmann;W. Kuhs;S. A. Klapp;K. Techmer;H. Klein;M. M. Murshed-M.;F. Abegg
利用X射线衍射（XRD）和低温扫描电镜（cryo-SEM）技术，对俄勒冈州海厄尼斯海岭南顶ODP第204航次6个钻探点的天然气水合物样品的保存状态进行了研究。气体水合物的分解状态的详细表征是必要的，因为没有加压高压釜工具用于采样和部分解离必须发生在恢复之前的淬火和储存在液氮中。在HASYLAB/ Hamburg通过同步加速器X射线衍射测量研究了来自16个不同层位的样品。同步加速器XRD数据的全轮廓拟合分析（“Rietveld方法”）提供了主要样品成分的定量相测定，例如气体水合物结构I（sI）、六方冰（Ih）和石英。每个样品中的冰含量（Ih）与由原始存在的孔隙水和来自分解的水合物的水组成的冻结水有关。通过衍射测量的水合氯离子含量在0和68重量%之间变化在我们测量的样本中。低水合物含量的样品通常在低温扫描电镜中显示出归因于广泛分解的微观结构特征。比较不同尺度的水合物的外观，保存的等级似乎主要与原始现有水合物的连续体积相关;解离锋似乎由致密冰基质中的微米级孔隙指示。
The state of preservation of natural gas hydrate samples, recovered from 6 sites drilled during ODP Leg 204 at southern summit of Hydrate Ridge, Oregon Margin, has been investigated by X-ray diffraction (XRD) and cryo-scanning-electron-microscopy (cryo-SEM) techniques. A detailed characterization of the state of decomposition of gas hydrates is necessary since no pressurized autoclave tools were used for sampling and partial dissociation must have occurred during recovery prior to the quench and storage in liquid nitrogen. Samples from 16 distinct horizons have been investigated by synchrotron X-ray diffraction measurements at HASYLAB/ Hamburg. A full profile fitting analysis (“Rietveld method”) of synchrotron XRD data provides quantitative phase determinations of the major sample constituents such as gas hydrate structure I (sI), hexagonal ice (Ih) and quartz. The ice content (Ih) in each sample is related to frozen water composed of both original existing pore water and the water from decomposed hydrates. Hydrate contents as measured by diffraction vary between 0 and 68 wt.% in the samples we measured. Samples with low hydrate content usually show micro-structural features in cryo-SEM ascribed to extensive decomposition. Comparing the appearance of hydrates at different scales, the grade of preservation seems to be primarily correlated with the contiguous volume of the original existing hydrate; the dissociation front appears to be indicated by micrometer-sized pores in a dense ice matrix.