EVALUATION OF POLYMER ALTERNATING WATERFLOODING IN MULTILAYERED HETEROGENEOUS WATERFLOODED RESERVOIR

Abstract

Polymer flooding is widely implemented to improve oil recovery since it can increase sweep efficiency and smoothen reservoir profile. However, polymer solution is somewhat difficult to be injected due to high viscosity thus, water slug is recommended to be injected before and during polymer injection in order to increase an ease of injecting this viscous fluid into the wellbore. Numerical simulation is performed to determine the most appropriate operating parameters to maximize oil recovery. Firstly, pre-flushed water should be injected until water breakthrough since not only it can increase polymer injectivity by flushing the oil around wellbore away, but also it ensures the connectivity between injector and producer. The smallest alternating water slug size which is 5 percent of polymer slug size is sufficient to increase injectivity of polymer slug and should be selected since large water slug setbacks time to inject the following polymer slug; however, slug size of alternating water is dependent on polymer desorption degree; with less degree of polymer desorption, slug size of alternating water should be increased. Concentration sorting does not show any significant benefit due to imbalance between polymer injectivity and displacement efficiency. Number of appropriate alternating water slug depends on polymer concentration; more alternative cycles should be implemented in case of high polymer concentration. In this study, three alternative cycles provide higher oil recovery than single-slug polymer in every polymer concentration. Residual resistance factor (RRF) dominates polymer injectivity when using low polymer concentration; oil production increases as RRF increases. Lastly, multi-slug polymer flooding yields better results compared to single-slug in all range of heterogeneity index when depositional sequence is coarsening upward. Oppositely, fining upward sequence has already obtained the benefit in terms of polymer injectivity from high permeability zone at the bottom of reservoir together with gravitational effects, consequently, multi-slug polymer flooding does not yield benefit over single-slug.