Given the search for recovery processes that are more efficient with lower water consumption and greenhouse gas emissions than Steam-Assisted Gravity Drainage (SAGD), solvent based recovery processes are a potential alternative. Vapor Extraction (VAPEX) and N-SolvTM are two potentially competing solvent recovery processes that offer water-free operation.
Although VAPEX has demonstrated success in laboratory experiments, it has not been demonstrated to be technically or commercially successful in the field due to the slow oil production rate. To improve oil recovery rate over that of VAPEX, the N-SolvTM process injects heated solvent into the reservoir to provide additional energy to the reservoir which enhances the reduction of the oil phase viscosity beyond that of solvent alone. The heated solvent is injected at pressures under its vapor pressure (at injection temperature) to ensure it is vapor. At the chamber interface, the solvent condenses releasing latent heat to the oil sand. Condensed solvent diffuses into bitumen and dilutes it reducing its viscosity to achieve mobility and drainage of the oil to the production well under the action of gravity.
In the research documented here, the mechanisms and effectiveness of the N-SolvTM process in a McMurray oil sand reservoir is investigated by fine grid (8 cm by 8 cm grid blocks in the cross well pair plane) thermal reservoir simulation. A sensitivity analysis of the N-SolvTM process was also done to explore possible ways to enhance oil production and reducing solvent retention in the depleted reservoir.
The results reveal that dynamics at the edge of the chamber – including phase change, oil viscosity reduction by elevated temperature and solvent diffusion, and the interaction between heat and mass transfer are complex. Also, in a dead oil reservoir, the injection of hot propane into oil sands reservoirs can yield comparable oil production rates to that of SAGD. Furthermore, solvent loss, which is a major concern, can be reduced by injecting at superheated conditions and relatively low pressures. Lastly, in the presence of solution gas and high connate water saturation in the reservoir, the performance of N-SolvTM suffers significantly.