Solvent Exsolution and Liberation from Different Heavy Oil–Solvent Systems in Bulk Phases and Porous Media: A Comparison Study

In this paper, experimental and numerical studies were conducted to differentiate solvent exsolution and liberation processes from different heavy oil–solvent systems in bulk phases and porous media. Experimentally, two series of constant-composition-expansion (CCE) tests in a PVT cell and differential fluid production (DFP) tests in a sandpacked model were performed and compared in the heavy oil–CO 2 , heavy oil–CH 4 , and heavy oil–C 3 H 8 systems. The experimental results showed that the solvent exsolution from each heavy oil–solvent system in the porous media occurred at a higher pressure. The measured bubble-nucleation pressures ( P n ) of the heavy oil–CO 2 system, heavy oil–CH 4 system, and heavy oil–C 3 H 8 system in the porous media were 0.24 MPa, 0.90 MPa, and 0.02 MPa higher than those in the bulk phases, respectively. In addition, the nucleation of CH 4 bubbles was found to be more instantaneous than that of CO 2 or C 3 H 8 bubbles. Numerically, a robust kinetic reaction model in the commercial CMG-STARS module was utilized to simulate the gas exsolution and liberation processes of the CCE and DFP tests. The respective reaction frequency factors for gas exsolution ( rff e ) and liberation ( rff l ) were obtained in the numerical simulations. Higher values of rff e were found for the tests in the porous media in comparison with those in the bulk phases, suggesting that the presence of the porous media facilitated the gas exsolution. The magnitudes of rff e for the three different heavy oil–solvent systems followed the order of CO 2 > CH 4 > C 3 H 8 in the bulk phases and CH 4 > CO 2 > C 3 H 8 in the porous media. Hence, CO 2 was exsolved from the heavy oil most readily in the bulk phases, whereas CH 4 was exsolved from the heavy oil most easily in the porous media. Among the three solvents, CH 4 was also found most difficult to be liberated from the heavy oil in the DFP test with the lowest rff l of 0.00019 min −1 . This study indicates that foamy-oil evolution processes in the heavy oil reservoirs are rather different from those observed from the bulk-phase tests, such as the PVT tests.