摘要
在CO2以超临界状态封存于油气藏时,储层中流体间的界面性质是影响封存效率和封存量的重要因素。利用分子动力学模拟的方法,对330 K、20 MPa混溶条件下(CO2+正己烷)/Na Cl溶液系统的界面微观性质进行了研究,分析了混溶相中CO2摩尔分数变化时,界面处CO2和正己烷的亲水、疏水特性及其影响,为CO2地质封存提供理论依据。研究发现,随着混溶相中CO2摩尔分数的增加,界面厚度及粗糙度增大,分子渗透加深,热波动加剧。界面上CO2与水之间更强的相互作用造成了CO2注入过程中界面张力的降低。CO2表现出类似于表面活性剂的性质,并在CO2摩尔分数为65%(质量分数为50%)时,其界面累积量以及正己烷的驱离量最大。界面处存在特殊的分子微观结构,CO2、水及正己烷分子呈现特殊的排布方式。
In the geological carbon dioxide （CO2） sequestration in abandoned oil reservoirs, there usually exists a fluid system including CO2, oil and brine, where the interplay between them is very important for the successful CO2 storage. In this paper, molecular dynamics simulations were carried out to investigate the interfacial characteristics of the CO2, n-hexane and NaCl solution system with different CO2 fractions at the miscible state. CO2 and n-hexane formed a miscible phase, and a clear interface was observed to separate the CO2 and n-hexane mixture with brine. Both the interfacial width and roughness increased with increasing CO2 composition, indicating the stronger interfacial interactions when water molecules contacted with CO2, leading to the reduction of interfacial tension. The surface adsorption of CO2 reached the maximum when CO2 molar fraction equaled to 65%, as well as the deficiency of n-hexane. This implied the surfactant feature of CO2 and the hydrophobicity of n-hexane towards the interface investigated. A special micro structure was observed at the interface, where CO2, water and n-hexane molecules had own preferred arrangement tendency. The special interfacial characteristics found could explain the experimental IFT phenomena and the microstructure variation in the CO2 injecting process, and could provide some theoretical guidance for CO2 sequestration.
出处
《化工学报》
EI
CAS
CSCD
北大核心
2015年第7期2601-2606,共6页
CIESC Journal
基金
国家自然科学基金项目(51106027)~~
关键词
超临界CO2
CO2地质封存
界面
分子模拟
supercritical carbon dioxide
CO2 geological storage
interface
molecular simulation
