Abstract:

Under the national strategy of carbon peak and carbon neutrality in China,utilizing CO₂ for enhanced oil recovery becomes an important means of CO₂ storage in oilfields. However, there are still challenges in the safe storage and transportation of liquid CO₂,in which gas impurities have a great influence on the thermodynamic properties of liquid CO₂.Seven common gas impurities were determined by the analysis of CO₂ samples obtained in the field,and the changes in physical properties of the CO₂ samples containing impurities were simulated by HYSYS and the molecular dynamics simulation method.The physical property diagrams were plotted and compared with those of pure CO₂.The results reveal that all seven impurities can enlarge the gas?liquid coexisting region in CO₂ phase diagrams,but the enlargement extent differs. The impurities mainly expand the gas?liquid coexisting region by changing the bubble point line,while the dew point line has little change.It is found by molecular dynamics simulation that the electrostatic potential energy plays a dominant role in the CO₂ mixture containing C₂H₆,C₃H₈,and C₂H₄.Therefore,compared with the results of the mixture containing H₂,CO,CH₄,and carbonyl sulfur (OCS),its macroscopic physical properties are less affected by temperature and pressure fluctuations.

Key words: Physical property of CO₂, Impurity, Molecular dynamics, CO₂ storage, Interaction energy

摘要：

在国家“双碳”战略背景下，利用CO₂提高油田采收率是封存CO₂的重要手段，但液态CO₂的安全储存、输送仍存在挑战，其中杂质气体对液态CO₂热力学物性的影响非常大。对现场取样的CO₂进行分析，确定了常见的7种杂质气体，并利用HYSYS、分子动力学模拟方法对含杂质CO₂的物性变化进行模拟计算，绘制物性版图并将其与纯CO₂的物性进行比较。研究表明，7种杂质均能使CO₂相图的气液共存两相区范围扩大，但不同杂质使气液共存两相区范围的扩大幅度不同；杂质主要通过泡点线的变化扩大气液共存两相区，而对露点线的变化影响不大；在含C₂H₆、C₃H₈、C₂H₄杂质的CO₂混合气体中静电势能占据主导作用，因此相比于含H₂、CO、CH₄、羰基硫（OCS）的混合气体，其宏观物性受温度、压力波动的影响较小。

关键词: CO₂物性, 杂质, 分子动力学, CO₂储存, 相互作用能