Research Progress of the Interfacial Tension in Supercritical CO2-water/oil System

Abstract

Carbon dioxide (CO2) is considered as one of major greenhouse gases, which has a significant contribution to global warming and has attracted more and more attention in recent years. So it s necessary to develop more efficient technologies to reduce CO2 emission. Carbon dioxide capture and sequestration (CCS) is one promising option to reduce CO2. CO2 flooding technique can enhance the oil recovery and achieve the storage of CO2 simultaneously. Therefore it is an important technology to support common development in terms of energy and environment. Under the high pressure, the interfacial tension (IFT) can affect fluid flow during the process of CO2 flooding greatly. Accordingly, there is an important significance to research miscible slug process and improve displacement efficiency. Hence the study of the IFT on supercritical CO2-water/oil system is indispensable.In order to understand the characteristic of IFT in-depth, this paper summarizes the IFT of CO2-water/oil system from the aspect of measuring methods, influencing factors and theoretical models. Currently there are less experimental data of IFT under the high pressures because of measuring difficulties in supercritical CO2-water/oil system. As one of the most effective measurement methods, the pendant drop method is developed gradually. This paper introduces the fundamental principles of several methods including selected plane method (SP), drop shape analysis (DSA) and axisymmetric drop shape analysis (ADSA). The relationships between pressure, temperature, concentration of CO2, salinity and IFT are summarized. Generally speaking, the IFT increases with the increasing pressure and salinity, while decreases with the increasing molar fraction of CO2. The effect of temperature on IFT is controversial in different researches. At the same time, this paper also presents the theoretical models of IFT in supercritical CO2-water/oil system. The work shows clearly the basic principles and applicable scopes of the statistical thermodynamics theories including density gradient theory (DGT) and density function theory (DFT). Finally, the directions should be strengthened concerning the study of IFT as follows: In terms of experiment, it is necessary to find out a method to measure the practical density difference by tracing system; Besides, a more accurate equation of state (EOS) should be constructed to calculate IFT. Therefore the proper measurement method, accurate injection pressure and concentration of CO2, rigorous theory and reliable mathematical model can be considered as research directions in future works.