Incorporating some heat injection along with the solvent injection appears to be the most viable option for improving the oil drainage rate of Vapex (Vapor Extraction) in extra-heavy oil formations. This study was aimed at quantifying the upper limit of oil rates achievable with heated solvent injection. Results of the performed research can also be used to assess the applicability of Vapex to naturally warm reservoirs and reservoirs with mobile oil in place.
The experimental phase of current research involved conducting Vapex experiments in a high-pressure physical model, packed with 250 Darcy sand, saturated with Athabasca bitumen (Mackay River) using propane as the solvent. The physical model was pre-heated to 40, 50 and 60 °C and propane was injected within 0.817 to 1.55 MPa pressure to investigate the effect of temperature elevation and injection pressure on Vapex performance.
Due to the mobility of the original oil in place at elevated temperatures, the total rate of oil production is controlled by two mechanisms: 1. solvent dissolution and oil mobilization at the boundaries of the vapor chamber 2. free fall gravity drainage of undiluted oil within the sand matrix beyond the solvent penetration zone. To evaluate warm Vapex performance under different operating conditions, the contribution of free fall gravity drainage to total recovery was experimentally and numerically determined.
Experimental results were compared against Vapex analytical models and a reported empirical correlation. The empirical correlation was modified based on the findings of the current experimental study by incorporating the effect of live oil viscosity into the original correlation.
The experimental results of warm Vapex tests were numerically simulated with a commercial compositional simulator, Computer Modelling Group’s (CMG) GEM. Bitumen characterization and thermo physical modeling of bitumen/propane system were performed as part of the numerical study. The developed simulation model verified by the experimental production data was used to extend the study to wider ranges of temperature.
Results of the current study indicates that elevating the reservoir temperature to 50oC without increasing the injection pressure, can improve production rate only by 70% and reservoir temperature elevation to above 60 oC is required to achieve more impressive rate increase of nearly 200% when Vapex is performed in heavy oil reservoirs.