温度及压强对CO2-盐水系统界面张力的影响

Temperature and pressure effect on interfacial tensions of CO_2-brine system

在超临界态CO_2封存于深部盐水层过程中,温度、压强等控制条件是影响封存效率和封存量的重要因素。应用分子动力学模拟的方法对343~373 K和6~35 MPa范围内的CO_2-Na Cl盐水系统进行了界面张力(IFT)及界面特性的研究,分析了IFT随温度及压强的变化关系,并观测到了压力平衡点pplateau;从分子尺度(物质密度、界面过余量、界面水合物密度)分析了IFT随压强、温度的变化,以及pplateau产生的原因。结果表明,pplateau前压强升高或温度降低将导致CO_2密度升高,IFT下降,而pplateau后IFT趋于稳定且受温度影响较小;CO_2的界面过余量及界面处水合物数量随压强及温度变化,与IFT的变化相反;高压下界面水合物密度的饱和现象可能是pplateau产生的重要原因。

Temperature and pressure are important effect factors of the efficiency and quantity of CO2 storage in the deep saline aquifers. Molecular dynamics（MD） simulation is applied to investigate the CO2-Na Cl systems in 343—373 K and 6—35 MPa, the interfacial tensions（IFT） which are obtained from the simulations are consistent with experimental results and the pressure balance point pplateau are observed as well in this paper. Meanwhile, the interfacial tension variations with the temperature and pressure are analyzed and the reasons of pplateau from the molecular viewpoint are explained. The results show that the pressure rise and temperature decline will increase CO2 density and decrease IFT before pplateau, but after pplateau the IFT will be stable and less affected by temperature. In addition, the changes of CO2 surface excess and the hydrate quantities with temperature and pressure showed the opposite trend compared with IFT variations, the saturation phenomena of hydrates at the interface under high pressure may be the fundamental reason of pplateau.