Determination of Diffusion Coefficients and Interface Mass-Transfer Coefficients of the Crude Oil−CO2 System by Analysis of the Dynamic and Equilibrium Interfacial Tensions

In this paper, a newly developed dynamic interfacial tension method has been applied to simultaneously determine the diffusion coefficients and interface mass-transfer coefficients of the crude oil−CO 2 system at high pressures and a constant temperature. Experimentally, the dynamic and equilibrium interfacial tensions of the crude oil−CO 2 system are measured by using the axisymmetric drop shape analysis (ADSA) technique for the pendant drop case. Theoretically, a mathematical model is formulated to obtain the time-dependent CO 2 concentration distribution inside the pendant oil drop. Then, in terms of a predetermined calibration curve of the measured equilibrium interfacial tension versus the calculated equilibrium CO 2 concentration in the crude oil, the dynamic interfacial tension at any time is calculated. Subsequently, an objective function is constructed to express the overall discrepancy between the numerically calculated and the experimentally measured dynamic interfacial tensions at different times. The CO 2 diffusion coefficient and the mass-transfer Biot number are used as adjustable parameters and thus determined once the global minimum objective function is achieved. The diffusion coefficient, the mass-transfer Biot number, and the interface mass-transfer coefficient of CO 2 mass transfer in a medium crude oil sample at P = 0.1−5.0 MPa and T = 27 °C are found to be 0.47−2.49 × 10 −9 m 2 /s, 2.3−6.8, 0.88−8.41 × 10 −5 m/s, respectively.