Natural gas hydrates (NGHs) are rising as an unconventional energy resource. The fundamental thermal characteristics of NGHs are of importance for natural gas exploitation from permafrost and oceanic sediments that are geomechanically deformed. Here, utilizing classic molecular dynamics simulations with all-atom (AA) and coarse-grained (CG) models of the methane guest molecule, the effects of mechanical strain on the thermal conductivity of sI-type methane hydrate are for the first time examined. Upon triaxial tension and compression, methane hydrate exhibits strong asymmetry in the stress responses. As the triaxial loads go from compression to tension, a reduction trend in the thermal conductivity is revealed for methane hydrate with both AA and CG models of methane, within a maximum reduction of over 44%. This reduction is because triaxial strain from compression to tension softens the phonon modes. Interestingly, there is a sudden rise in thermal conductivity at critical triaxial strain of 0.06, originating from that, at which, the phonon modes are hardened and the peaks of radial distribution functions are shifted back. This study provides important information on the thermal conductivity of methane hydrate, which is helpful for the practical production of natural gas from geo-deformed NGH-bearing sediments via a heating technique as well as evaluating their stability.

中文翻译：

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机械变形在 sI 型甲烷水合物热输运中的作用

天然气水合物 (NGH) 作为一种非常规能源正在崛起。NGH的基本热特性对于从地质力学变形的永久冻土和海洋沉积物中开采天然气具有重要意义。在这里，利用甲烷客体分子的全原子 (AA) 和粗粒 (CG) 模型进行经典分子动力学模拟，首次研究了机械应变对 sI 型甲烷水合物热导率的影响。在三轴拉伸和压缩时，甲烷水合物在应力响应中表现出强烈的不对称性。随着三轴载荷从压缩到拉伸，在甲烷的 AA 和 CG 模型中，甲烷水合物的热导率呈现下降趋势，最大下降幅度超过 44%。这种减少是因为从压缩到拉伸的三轴应变软化了声子模式。有趣的是，在临界三轴应变为 0.06 时，热导率突然上升，这源于此时声子模式变硬并且径向分布函数的峰值向后移动。该研究提供了有关甲烷水合物热导率的重要信息，有助于从地质变形的含水合物沉积物中实际生产天然气通过加热技术以及评估它们的稳定性。