Abstract
A solvent process for heavy oil recovery is described in which an infill injection well is used to inject a cold solvent into neighboring steam chambers once they merge. Simulation results are presented summarizing acceleration in oil recovery and the beneficial impact on energy consumption.
Approximately 60% of injected energy in SAGD process is retained in the reservoir. If a cold solvent is injected into a SAGD formation, it will use the stored energy to vaporize and spread within the steam chamber, while at the same time effectively cooling it. An infill injection well is drilled near the top of the rich pay zone and half way between two neighboring SAGD well pairs. Once the steam chambers merge, cold solvent is injected targeting the outer peripheries of the steam chamber. A small amount of non-condensable gas can also be added to help with pressure maintenance. Cooling of steam chamber enhances solubility of solvent in the bitumen phase and accelerates recovery. Once a secondary peak oil rate is observed due to the cold solvent, proportion of non-condensable gas to solvent in the injected fluid is steadily increased and eventually steam injection is completely ceased and the process switches to blow down phase with 100% non-condensable gas injection.
Simulation results show that injection of liquid propane and traces of non-condensable gas through the infill injection well provides pressure support and immediately reduces the amount of steam injection required through the primary SAGD injection well by 40-60%. This is followed by a steady increase in oil production rate aided by the viscosity reduction due to propane solubility. A secondary oil production rate peak, comparable to the original peak observed with steam, is achieved. A variation of this process was also simulated for mature SAGD formations, where cold propane injection is accompanied by total steam injection cessation, showing advantageous results.
Cold Solvent Process separates out injection of solvent from steam resulting in a much simpler facility design. No additional energy is used to vaporize the solvent at the wellhead. Unlike steam/solvent co-injection processes, solvent is delivered to the cold bitumen interface directly and extracts useful energy from the residual heat in the rock matrix.
