Experimental Investigation on the Effect of Asphaltene Types on the Interfacial Tension of CO2–Hydrocarbon Systems

Interfacial tension (IFT) is known as the critical parameter affecting the efficiency of CO2 flooding during the enhanced oil recovery (EOR) process. Besides, the asphaltene precipitation phenomenon is reported as the most significant problem during CO, injection into asphaltenic oil reservoirs. Accordingly, it is important to examine the effect of asphaltene precipitation on the IFT behavior of the oil CO2 system at reservoir conditions. The main objective of this research work is to study of the effect of asphaltene and its type on the IFT behavior of the oil-CO2 system. The IFT between pure CO2 and a model oil both with and without asphaltene was measured using an axisymmetric drop shape analysis (ADSA) technique over a wide range of pressures and a constant temperature of 323 K. The asphaltene particles used for the work were precipitated and separated from three different crude oil samples, each having different physical properties. The model oil, consisted of SO vol % n-heptane and 50 vol % toluene ("hepto150") and was doped with asphaltene particles at a concentration of 4 wt % to ensure that the particles remained suspended in the model oil over the range of pressures studied. The results showed that the IFT between CO2 and the model oil is inversely proportional to the pressure and that the constant proportionality is affected by the presence of asphaltene particles. In fact, the asphaltene aggregates formed in the model oil lead to a reduction in the magnitude of this constant. This, in turn, could result in lower CO2 solubility. Also, the effect of the asphaltene molecular structure on IFT of CO2 model oil was investigated in this work. It was shown that the hydrogen deficiency and aromaticity of asphaltene molecules were important parameters that could significantly affect the IFT for CO2-model oil.