Optimized solvent-aided steam-flooding strategy for recovery of thin heavy oil reservoirs

Stochastic optimization based on a simulated annealing method was carried out to determine the optimum steam and steam-solvent flooding strategies in a thin (4 m) heavy oil reservoir both in the absence and presence of a bottom water zone. The steam injection pressure optimization case determined a technically feasible operating strategy. However, the cumulative energy to produced oil ratio (cEOR) realized from the optimized process is high. In comparison, the solvent-aided steam optimization case achieved an operating strategy with a much lower cEOR and cumulative water-to-oil ratio (cWOR) than those in the optimized injection pressure-only strategy. We observed that a solvent-rich channel forms at the top of the reservoir after solvent breakthrough occurs at the production well. The formation of the solvent-rich channel led to oil-solvent mixing at the periphery of the channel as well as heat transfer to oil beyond the channel, which in turn resulted in better recovery performance. In the presence of a bottom water zone, the optimized steam injection pressure optimization strategy was found to perform poorly. However, the optimized solvent-aided strategy achieved superior performance. With solvent injection, the presence of the bottom water zone enhanced mixing of solvent and oil yielding improved oil recovery performance.