The production of methane (CH₄) from natural gas hydrate deposits via molecular replacement by injected, thermodynamically more favorable, carbon dioxide (CO₂) is a promising method of energy production and carbon sequestration. However, the viability of this technique is constrained by mass-transfer limitations, which are in turn associated with diffusion of the injected CO₂ into the hydrate-bearing sediment layers. Generally, the coupled heat- and mass-transfer phenomena associated with this replacement process in complex heterogeneous porous media are poorly understood. To facilitate the noninvasive pore-scale study of this replacement process (ultimately in sediment cores) using a range of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques, a novel NMR-compatible sediment holder has been designed and constructed. Via the provision of centralized sample cooling, sample temperature control is achieved at high pressures while keeping the NMR magnet system at the required temperature. Hydrate formation and dissociation processes in model porous media were successfully investigated using a CH₄/C₂H₆ mixture and CO₂. Novel one-dimensional (1D) MRI images of the residual liquid water and hydrocarbon gas were acquired during the hydrate formation and dissociation processes using a single-point ramped imaging with T₁ enhancement (SPRITE) MRI pulse sequence. Interleaved NMR T₂ relaxation measurements were also obtained to interrogate the pores sizes occupied by the residual water. From these results, the water distribution and subsequent hydrate-formation behavior have been spatially and temporally resolved throughout the porous media.

中文翻译：

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用于多孔介质中气体水合物研究的NMR兼容样品池

通过注入热力学上更有利的二氧化碳（CO ₂）通过分子置换从天然气水合物沉积物中生产甲烷（CH ₄）是一种有前途的能源生产和碳固存方法。但是，该技术的可行性受到传质限制的限制，传质限制又与注入的CO _2的扩散有关进入含水合物的沉积层。通常，在复杂的非均质多孔介质中与这种置换过程相关的耦合的传热和传质现象知之甚少。为了使用一系列核磁共振（NMR）和磁共振成像（MRI）技术促进这种置换过程（最终在沉积物核中）的非侵入性孔隙尺度研究，已设计和构建了一种新型的NMR兼容的沉积物支架。通过提供集中的样品冷却，可以在高压下实现样品温度控制，同时将NMR磁体系统保持在所需的温度下。使用CH ₄ / C ₂ H ₆成功研究了模型多孔介质中水合物的形成和解离过程混合物和CO ₂。使用T ₁增强（SPRITE）MRI脉冲序列的单点倾斜成像，在水合物形成和分解过程中获取了残留的液态水和碳氢化合物气体的新型一维（1D）MRI图像。还获得了交错的NMR T ₂弛豫测量值，以查询残留水所占据的孔径。从这些结果来看，水分布和随后的水合物形成行为已在整个多孔介质中在空间和时间上得到解决。