Abstract:

CO₂ enhanced oil recovery technique uses CO₂ to extract the remaining oil trapped in the stratum to enhance oil recovery and achieve CO₂ landfill. Since CO₂ can reduce the interfacial tension of crude oil, the interfacial tension data of CO₂-crude oil system is an important basic data of CO₂ Enhanced Oil recovery process. In this work, the interfacial tension data of CO₂-cyclopentane/cyclohexane/cyclooctane/toluene/ethylbenzene/ethylcyclohexane were measured by pendent drop method at 40—120℃ in the pressure range of 0.27—14.70 MPa. The effects of pressure, temperature, carbon number and molecular structures on interfacial tension are analyzed. The results show that the interfacial tension values decrease with the pressure increasing when the temperature is constant. And at lower pressure, interfacial tension values decrease with the temperature increasing. But at higher pressure, it shows an opposite trend. The interfacial tension values of CO₂-similar morphology structure increase with the carbon number. And the intermolecular forces have a certain effect on the interfacial tension. One empirical model for the interfacial tension is presented by analyzing the influences of these factors and summarizing the experimental data of CO₂-crude oil (n-alkanes, cycloalkanes, aromatic hydrocarbons) binary system. In the model, the temperature, the pressure, the carbon number and the acentric factor were considered. The square of the correlation coefficient (R ²), root mean square error (RMSE) and average relative deviation (AARD) were 0.958, 1.12, 11.01% respectively.

Key words: interfacial tension, carbon dioxide, cycloalkanes, aromatics, CO₂ enhanced oil recovery

摘要：

CO₂驱油技术是利用CO₂采出被束缚在地层中的剩余油，提高采收率，同时实现CO₂掩埋。由于CO₂可降低原油的界面张力，CO₂-原油系统的界面张力数据是CO₂采油技术的重要基础数据。本研究采用悬滴法，选取原油系统中环烷烃和芳香烃典型代表，测定了40~120℃，0.27~14.70 MPa下，CO₂-环戊烷/环己烷/环辛烷/ 甲苯/乙苯/乙基环己烷六个二元体系的界面张力。分析了压力、温度、碳原子数及烷烃分子结构对界面张力的影响。结果表明，界面张力与压力呈线性关系；较低压力下，界面张力随温度的升高而降低，在较高压力下则呈现相反趋势；CO₂-形态结构相同组分的界面张力随着碳数的增加而增大；分子间作用力对界面张力存在一定的影响。通过分析多种因素的影响，总结现有的CO₂-原油(正构烷烃、环烷烃、芳香烃)实验数据，提出关联方程，将表面张力关联为温度、压力、碳原子数和偏心因子的函数，相关系数(R² )为0.958，均方根误差(RMSE)及平均相对偏差(AARD)分别为1.12和11.01%。

关键词: 界面张力, 二氧化碳, 环烷烃, 芳香烃, CO₂驱油