Abstract The equilibrium phase boundary of gas hydrates divides the phase diagram of the gas–water system into two zones, i.e., one with hydrates and the other without hydrates. Motivations to investigate the phase boundary of gas hydrates formed by CH4, CO2, and their mixture in saline water stem from its foundation roles in e.g., flow assurance, energy recovery, and CO2 sequestration. In this work, a thermodynamic model has been developed to improve the prediction accuracy of the equilibrium phase boundary of CH4, CO2, and binary CH4-CO2 hydrates in both pure and saline water. A different set of reference properties are employed in this newly developed model. A database collecting the most up to date measured phase boundary of gas hydrates have been newly generated, containing 728 data points with the temperature ranging from 261.8 K to 300 K, and the concentration of NaCl solutions up to 24.12 wt%, which is used for parameter regression and model validation. The impacts of temperature, NaCl, and gas composition on the phase boundary of gas hydrates are well captured by the developed model. A convergence trend of the phase boundary curves of the binary CH4-CO2 hydrates in the high-temperature range is observed and explained with the Clausius-Clapeyron equation. The overall average absolute relative deviation (AARD) of the calculated phase boundary pressure of the 728 points is 4.42%. The performance of the newly developed model is satisfactory considering the discrepancies among measured data from various sources.

中文翻译：

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在 NaCl 溶液中形成的 CH4、CO2 和二元 CH4-CO2 水合物的相界

摘要 天然气水合物的平衡相界将气-水系统相图划分为两个区域，一个有水合物，另一个没有水合物。研究由 CH4、CO2 及其混合物在咸水中形成的天然气水合物的相界的动机源于其在流动保证、能量回收和 CO2 封存等方面的基础作用。在这项工作中，开发了一种热力学模型，以提高纯水中 CH4、CO2 和二元 CH4-CO2 水合物平衡相界的预测精度。在这个新开发的模型中采用了一组不同的参考属性。新增天然气水合物最新实测相界数据库，包含728个温度261.8K~300K数据点，NaCl 溶液的浓度高达 24.12 wt%，用于参数回归和模型验证。开发的模型很好地捕捉了温度、NaCl 和气体成分对天然气水合物相界的影响。观察并用Clausius-Clapeyron方程解释了高温范围内二元CH4-CO2水合物相边界曲线的收敛趋势。728个点的计算相界压力的总体平均绝对相对偏差（AARD）为4.42%。考虑到来自不同来源的测量数据之间的差异，新开发的模型的性能令人满意。和天然气水合物相边界上的气体成分被开发的模型很好地捕获。观察并用Clausius-Clapeyron方程解释了高温范围内二元CH4-CO2水合物相边界曲线的收敛趋势。728个点的计算相界压力的总体平均绝对相对偏差（AARD）为4.42%。考虑到来自不同来源的测量数据之间的差异，新开发的模型的性能令人满意。和天然气水合物相边界上的气体成分被开发的模型很好地捕获。观察并用Clausius-Clapeyron方程解释了高温范围内二元CH4-CO2水合物相边界曲线的收敛趋势。728个点的计算相界压力的总体平均绝对相对偏差（AARD）为4.42%。考虑到来自不同来源的测量数据之间的差异，新开发的模型的性能令人满意。728个点的计算相界压力的总体平均绝对相对偏差（AARD）为4.42%。考虑到来自不同来源的测量数据之间的差异，新开发的模型的性能令人满意。728个点的计算相界压力的总体平均绝对相对偏差（AARD）为4.42%。考虑到来自不同来源的测量数据之间的差异，新开发的模型的性能令人满意。