Supercritical carbon dioxide (scCO 2) microemulsion was formed by supercritical CO 2 , H 2 O, sodium bis(2-ethylhexyl) sulfosuccinate (AOT, surfactant) and C 2 H 5 OH (co-surfactant) under pressures higher than 8 MPa at 45 oC. The fundamental characteristics of the scCO 2 microemulsion and the minimum miscibility pressure (MMP) with Daqing oil were investigated with a high-pressure falling sphere viscometer, a high-pressure interfacial tension meter, a PVT cell and a slim tube test. The mechanism of the scCO 2 microemulsion for enhancing oil recovery is discussed. The results showed that the viscosity and density of the scCO 2 microemulsion were higher than those of the scCO 2 fluid at the same pressure and temperature. The results of interfacial tension and slim tube tests indicated that the MMP of the scCO 2 microemulsion and crude oil was lower than that of the scCO 2 and crude oil at 45 oC. It is the combined action of viscosity, density and MMP which made the oil recovery efficiency of the scCO 2 microemulsion higher than that of the scCO 2 fluid.
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