Formation of natural gas hydrates during processing and transport of natural gas has historically been a significant motivator for hydrate research. The last three decades have also seen the focus increasingly shifting towards CH₄ hydrates as a potential energy source. And in the context of climate changes, the impact of hydrate-related processes is coming more to the forefront as well. This interest is not only limited to leakage fluxes of CH₄ from natural gas hydrates but also flux from conventional hydrocarbon systems entering the seafloor at temperature and pressure allowing for hydrate formation. Alternative ways to treat formally overdetermined hydrate systems is an important focus in this work. The most common method used for assessment of hydrate phase transitions involves several fitted parameters to calculate the free energy difference between liquid water and empty hydrate. This technique calls for an empirical fitting of fundamental thermodynamic properties. Numerical codes based on this method limit the models to hydrate formation only from free gas and liquid water. This is at least true for all commercial and academic codes that were examined prior to this work. This work addresses the advantages in using residual thermodynamics for all phases, including hydrates. In addition to making it possible to handle many alternative hydrate routes leading to hydrate formation or dissociation, the presented method also opens a way to calculate a variety of needed thermodynamic properties (e.g., enthalpies of pure components and mixtures) in a simple and consistent way. This approach will be illustrated through calculations of various hydrate phase transitions, examples of free energy calculations for comparison of phase stability, and calculation of enthalpies of hydrate formation. Calculated enthalpies are compared with experimental data as well as results derived from applying the Clapeyron equation. Mechanisms for conversions of in situ CH₄ hydrate to facilitate safe CO₂ storage are also discussed. A very simple Clapeyron-based scheme for calculation of enthalpies for hydrate phase transitions is also proposed.

中文翻译：

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使用统一参考状态的水合物系统的热力学

在天然气加工和运输过程中形成天然气水合物一直是水合物研究的重要推动因素。在过去的三个十年中，重点也越来越多地转向作为潜在能源的CH ₄水合物。在气候变化的背景下，水合物相关过程的影响也越来越突出。这种兴趣不仅限于 CH _{4 的}漏磁通来自天然气水合物，但也有来自常规碳氢化合物系统的通量，这些系统在允许形成水合物的温度和压力下进入海底。处理正式超定水合物系统的替代方法是这项工作的重点。用于评估水合物相变的最常用方法涉及几个拟合参数来计算液态水和空水合物之间的自由能差。这种技术需要对基本热力学特性进行经验拟合。基于此方法的数字代码将模型限制为仅由游离气体和液态水形成水合物。至少对于在这项工作之前检查过的所有商业和学术代码都是如此。这项工作解决了对所有相（包括水合物）使用残余热力学的优势。除了可以处理导致水合物形成或解离的许多替代水合物路线之外，所提出的方法还开辟了一种以简单且一致的方式计算各种所需热力学性质（例如，纯组分和混合物的焓）的方法. 这种方法将通过各种水合物相变的计算、用于比较相稳定性的自由能计算示例以及水合物形成焓的计算来说明。计算的焓与实验数据以及应用克拉珀龙方程得出的结果进行比较。原位 CH 的转化机制 所提出的方法还开辟了一种以简单且一致的方式计算各种所需热力学特性（例如，纯组分和混合物的焓）的方法。这种方法将通过各种水合物相变的计算、用于比较相稳定性的自由能计算示例以及水合物形成焓的计算来说明。计算的焓与实验数据以及应用克拉珀龙方程得出的结果进行比较。原位 CH 的转化机制 所提出的方法还开辟了一种以简单且一致的方式计算各种所需热力学特性（例如，纯组分和混合物的焓）的方法。这种方法将通过各种水合物相变的计算、用于比较相稳定性的自由能计算示例以及水合物形成焓的计算来说明。计算的焓与实验数据以及应用克拉珀龙方程得出的结果进行比较。原位 CH 的转化机制 以及水合物生成焓的计算。计算的焓与实验数据以及应用克拉珀龙方程得出的结果进行比较。原位 CH 的转化机制 以及水合物生成焓的计算。计算的焓与实验数据以及应用克拉珀龙方程得出的结果进行比较。原位 CH 的转化机制₄水合物促进安全的 CO ₂储存也被讨论。还提出了一种非常简单的基于克拉珀龙的方案，用于计算水合物相变的焓。