Quantification of Mutual Mass Transfer Coupled with Heat Transfer for CO2/C3H8-Heavy Oil Systems Under Reservoir Conditions

Summary Experimental and theoretical methods have been developed to quantitatively assess the heat and bidirectional mass transfer between a hot solvent (i.e., CO2 and C3H8) and heavy oil. Experimentally, we performed diffusion experiments for hot solvent-heavy oil systems at elevated pressures and temperatures using a pressure/volume/temperature (PVT) setup. The dynamic volume change of the oleic phase has been continuously measured and recorded throughout each experiment. At the conclusion of each test, gas chromatography (GC) analysis has been conducted on the collected gas samples. Theoretically, a diffusion model has been integrated with heat transfer to determine the mutual diffusivities for the hot CO2/C3H8-heavy oil systems by incorporating the volume-translated (VT) Peng-Robinson equation of state (PR EOS) together with the modified alpha functions and acentric factor redefined at Tr = 0.6. The mutual diffusivities can be determined once the computed parameters, including oil swelling factors and gas composition, match the measured ones. Due to solvent dissolution, heavy oil is found to swell faster initially as both heat and mass transfer contribute to the oil swelling. After the system temperature is stabilized, the volume of the diluted oil expands slowly as a result of the ongoing mass transfer. The extraction process was evident during the experiments with the presence of oil components in the collected gas samples, and it was found to be stronger at a higher temperature. The diffusivities determined using different alpha functions in the PR EOS are similar, but the newly defined acentric factor with the optimum alpha function minimizes the deviation between the measured and computed parameters. In addition to new experimental data, the bidirectional mass transfer between solvent and heavy oil has been quantified for the first time by coupling heat transfer.