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. (C) 2013 Elsevier Ltd. All rights reserved.