EVALUATION OF ALTERNATE WATER-POLYMER INJECTION PARAMETERS USING NUMERICAL SIMULATION

Abstract

Finding an efficient injection strategy using polymers to reduce water-oil mobility ratio and improve sweep efficiency relies on many parameters. To overcome the disadvantages (injectivity loss and high costs) of injecting a continuous polymer bank, an alternative is to alternate water-polymer injection cycles, combining the benefits of water flooding (better injectivity) and polymer flooding (better sweep). A common approach is the injection of a continuous polymer bank after a period of water injection. In this case, parameters of the polymer bank (i.e. duration and starting date of the bank) are control variables and must optimized for the strategy. This work (1) evaluates the impact of alternate water-polymer injection parameters and (2) analyzes the viability of using alternate water-polymer cycles to improve the performance of the polymer flooding strategy, previously optimized for continuous injection bank. We analyze the cycle period, starting date of the cycle, and initial injected fluid using net present value (NPV) and other indicators (cumulative oil and water productions and cost of polymer injection). We apply the study to two reservoir models based on offshore heavy oil fields. The results show that cycle parameters can impact strategy performance significantly and that proper evaluation can benefit production. We observed that reducing the cycle period helped maintain injection flow at higher levels, avoiding the reduction of oil production by pressure depletion. We also noted that the cycle must start in the first years after the beginning of injection. It is important to identify the most influential parameters to set injection levels to support beneficial effects of both methods, and adjust the optimum amount of polymer to be injected.