The effects of CO2 pressure, temperature and concentration on asphaltene precipitation induced by CO2 were studied using a high-pressure vessel, interfacial tensiometer, Fourier transform infrared(FTIR) and drill core displacement experimental apparatus. The results indicated that the content of asphaltene in crude oil decreased, and the interfacial tension between a model oil and distilled water increased, with an increase of CO2 pressure, decrease of temperature and increase of molar ratio of CO2 to crude oil when CO2 contacted crude oil in the high pressure vessel. The content of asphaltene in sweepout oil and the permeability of test cores both also decreased with an increase of CO2 flooding pressure. The main reason for changes in content of asphaltene in crude oil, in interfacial tension between model oil and distilled water and in the permeability of the test core is the precipitation of asphaltene which is an interfacially active substance in crude oil. Precipitation of asphaltene also blocks pores in the drill core which decreases the permeability.
In order to investigate the effect of organic liquid molecular structure and the intermolecular force operating with CO2 molecules and organic liquid molecules on interfacial tension(IFT) between CO2 and organic liquid at the first contact, the interfacial tension between CO2 and hexane, octane, ethanol and cyclohexane at different temperatures and pressures is measured by using the pendant drop method and the axisymmetric drop shape analysis(ADSA). The results show that the interfacial tension between CO2 and organic liquids is affected by the polarity and the structure of the organic liquid molecule obviously. The intermolecular force operating within CO2 molecules or organic liquid, and that between CO2 and organic liquids molecules play a dominate role on the interfacial tension between CO2 and the organic liquids.
