We present the results of dynamic in-situ 3D X-ray imaging of methane hydrates microstructure during methane hydrate formation and decomposition in sand samples. Short scanning times and high resolution provided by synchrotron X-rays allowed for better understanding of water movement and different types of gas-hydrate formation. Complementing previous observations, we conclude that the process of gas-hydrate formation is accompanied by the water movements caused by cryogenic water suction that happens in short sequences with longer equilibrium states in between (when the water is immobile). Based on the 3D microstructure we identified two types of gas-hydrate formation: (i) into the gas pockets and (ii) inside water volumes. During the decomposition in the self-preservation mode (pressure drop at negative temperatures) the latter remains more stable compared to the hydrate formed as growing into the gas pocket. This means that the history of the gas-hydrate formation influences its behaviour at the decomposition stage (e.g. gas-hydrate production).

中文翻译：

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多孔介质中甲烷水合物形成和自我保存的动态原位成像

我们展示了在砂岩样品中甲烷水合物形成和分解过程中甲烷水合物微观结构的动态原位 3D X 射线成像结果。同步加速器 X 射线提供的短扫描时间和高分辨率允许更好地了解水运动和不同类型的天然气水合物形成。补充先前的观察，我们得出结论，天然气水合物的形成过程伴随着由低温吸水引起的水运动，这种运动发生在短序列中，中间有较长的平衡状态（当水静止时）。基于 3D 微观结构，我们确定了两种类型的天然气水合物形成：（i）进入气袋和（ii）内部水体积。在自我保存模式下的分解过程中（负温度下的压降），与生长到气穴中形成的水​​合物相比，后者保持更稳定。这意味着天然气水合物形成的历史影响其在分解阶段的行为（例如天然气水合物生产）。