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以水合物的形式封存CO_2和置换海底的天然气（CH_4）水合物需要对CO_2-CH_4混合水合物的四相平衡状态及数据有清楚的了解。本文通过实验和模型计算对不同组分的CO_2-CH_4混合水合物的较高四相区（Q2）相平衡进行了测定和表述。实验温度范围为273.16～297 15 K,压力范围分为0～10 MPa。四相区的温度压力范围分别是283.51到287.04 K和4.74到8.37 MPa,甲烷的摩尔组份为0～0.225。结果揭示了相平衡温度和压力随着甲烷组分而变化情况以及四相区的范围和临界点,同时还给出了CO_2-CH_4混合气体水合物在四相状态下的融化开始和融化结束点。实验结果与热力学模型计算得出的CO_2-CH_4混合气体水合物相平衡结果进行比较,两者很好吻合,四相平衡区域的存在范围得以明确。

The phase equilibrium data for the upper-quadruple（H-W-L-V） phase states of CO_2-CH_4 mixed hydrates are needed for application of the replacement of CH_4 hydrate with CO_2.In this paper,the upper-quadruple（Q2） phase equilibrium properties of CO_2-CH_4 mixed hydrates were investigated by using a visual experimental apparatus in the temperature range of 273.16～297.15 K and pressure up to 10MPa and verified by calculation with thermodynamic models.The coexisting of upper-quadruple phase region was identified in 4.46～8.4 MPa,283.09～287.9 K and 0～0.225 methane mole fraction.It is found that the range of temperature and pressure for Q2 phase coexistence increases with the methane concentration until the retrograde of the quadruple phase is reached.The start and end melting of the CO_2-CH_4 mixed hydrates in the upper quadruple states were tested in constant volume condition.The tested results were also compared with the predictions with combination of the thermodynamic models for the mixed gas hydrate and the CO_2-CH_4 vapor-liquid equilibrium.The existence of the Q2 phase equilibrium region and its extension are clarified.