Abstract
This article presents a numerical assessment of chemical flooding strategies for enhanced oil recovery (EOR) in a pore-fractured carbonate reservoir using the CMG STARS reservoir simulator. Carbonate reservoirs are characterized by complex pore-fracture systems and high heterogeneity, which often result in poor sweep efficiency and significant residual oil saturation after conventional water flooding. To improve recovery performance, several conformance control methods, including polymer flooding, surfactant flooding, pre-gel treatment, and combined surfactant-polymer injection, were evaluated under different injection scenarios. Reservoir performance was assessed using key indicators such as cumulative oil production, incremental oil recovery, water cut, sweep efficiency, and production sustainability. The simulation results demonstrated that all chemical flooding methods outperformed conventional water injection, although their effectiveness varied depending on chemical concentration, injection volume, and operational conditions. Polymer flooding improved sweep efficiency by increasing the viscosity of the injected fluid, while surfactant flooding reduced interfacial tension and enhanced oil mobilization. Pregel treatment exhibited the highest improvement in several production scenarios by effectively controlling fluid movement and reducing excessive water production. The combined surfactant-polymer strategy also showed strong synergistic effects, providing stable production and significant incremental oil recovery. Sensitivity analyses identified optimal chemical concentrations that balanced recovery performance with operational feasibility. Application of the optimized strategies to the Zhanazhol oilfield model confirmed their technical effectiveness and long-term benefits. The findings demonstrate that carefully designed chemical flooding programs can substantially increase oil recovery, improve conformance control, and reduce water cut in complex carbonate reservoirs. The results provide practical guidance for selecting and optimizing chemical EOR techniques and support future field implementation in heterogeneous pore-fractured carbonate formations.