Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X-ray computed tomographic microscopy
Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X-ray computed tomographic microscopy
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DOI：
10.1002/2015gc005811
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发表时间：
2015-06-01
影响因子：
3.5
通讯作者：
Kuhs, Werner F.
中科院分区：
文献类型：
--
作者：
Chaouachi, Marwen;Falenty, Andrzej;Kuhs, Werner F.
天然气水合物在沉积基质中的形成过程对所形成的聚集体的物理和输运性质至关重要。这一过程从未在亚微米分辨率下原位观察到。在这里，我们报告的同步加速器为基础的微层析成像研究，在276 K的天然气水合物的成核和生长过程中观察到的各种沉积基质，如天然石英（有和没有混合物的蒙脱石型粘土）或玻璃珠具有不同的表面性质，在不同的水饱和度。使用从天然气水合物分解获得的初生水和亚稳富气水。氙气被用来增强气体水合物和流体相之间的密度对比度。可以很容易地确定成核位置，并清楚地建立各种生长模式。在未饱和的沉积物与幼年水，成核开始在水-气界面，导致在最初的几微米厚的气体水合物膜，进一步生长进行，形成10-20 μ m大小的等距单晶。从富气水中生成的气体水合物的生长遵循不同的模式，通过在大量液体中成核产生多面体单晶。在这两种情况下的一个显著特征是在气体水合物和石英颗粒表面之间系统地出现了厚度达几微米的流体相膜。这些微观结构的研究结果是相关的定量岩石物理建模的天然气水合物在沉积基质中的未来努力，并解释了地震/声波的异常衰减。
The formation process of gas hydrates in sedimentary matrices is of crucial importance for the physical and transport properties of the resulting aggregates. This process has never been observed in situ at submicron resolution. Here we report on synchrotron-based microtomographic studies by which the nucleation and growth processes of gas hydrate were observed at 276 K in various sedimentary matrices such as natural quartz (with and without admixtures of montmorillonite type clay) or glass beads with different surface properties, at varying water saturation. Both juvenile water and metastably gas-enriched water obtained from gas hydrate decomposition was used. Xenon gas was employed to enhance the density contrast between gas hydrate and the fluid phases involved. The nucleation sites can be easily identified and the various growth patterns are clearly established. In sediments under-saturated with juvenile water, nucleation starts at the water-gas interface resulting in an initially several micrometer thick gas hydrate film; further growth proceeds to form isometric single crystals of 10-20 mu m size. The growth of gas hydrate from gas-enriched water follows a different pattern, via the nucleation in the bulk of liquid producing polyhedral single crystals. A striking feature in both cases is the systematic appearance of a fluid phase film of up to several micron thickness between gas hydrates and the surface of the quartz grains. These microstructural findings are relevant for future efforts of quantitative rock physics modeling of gas hydrates in sedimentary matrices and explain the anomalous attenuation of seismic/sonic waves.