Coupling heat and mass transfer for determining individual diffusion coefficient of a hot C3H8–CO2 mixture in heavy oil under reservoir conditions

Abstract By characterizing heavy oil as multiple pseudocomponents, a generalized methodology has been developed to determine both apparent and individual diffusion coefficients by coupling heat and mass transfer for hot C 3 H 8 –CO 2 –heavy oil systems under reservoir conditions with consideration of swelling effect. Experimentally, a visualized PVT setup has been used to conduct diffusion tests for hot C 3 H 8 –CO 2 –heavy oil systems with different C 3 H 8 concentrations under a constant pressure. The dynamic volume change of liquid-phase is monitored and recorded during the measurements. Theoretically, the volume-translated Peng–Robinson equation of state (PR EOS) with a modified alpha function has been incorporated to develop a two-dimensional heat and mass transfer model for the hot C 3 H 8 -enriched CO 2 –heavy oil systems, while the heavy oil sample has been characterized as three pseudocomponents for accurately predicting phase behavior of the aforementioned systems. The binary interaction parameter (BIP) correlations are tuned with the experimentally measured saturation pressures, while the tuned BIPs are validated with the measured equilibrium swelling factors. Both the individual diffusion coefficient of each component and the apparent diffusion coefficients of C 3 H 8 –CO 2 mixtures are determined once the discrepancy between the measured and calculated dynamic swelling factors of heavy oil has been minimized. Compared to CO 2 alone, C 3 H 8 –CO 2 mixtures lead to enhanced swelling effect of heavy oil, while a higher C 3 H 8 concentration achieves a faster dissolution and a larger dynamic swelling factor. Thus, C 3 H 8 preferentially diffuses into heavy oil than CO 2 at the same conditions for C 3 H 8 –CO 2 –heavy oil systems.