This study aims at developing a robust geochemical simulation model of pH-sensitive polymer flooding in the context of improved oil recovery. The model can accommodate changes in aqueous solution chemistry and mineral surfaces. The model was calibrated using laboratory data for pH and water chemistry during brine flush and subsequent acid flood. This model was validated using experimental data for citric acid and HCl injections in Berea sandstone. The matching procedure consists of adjusting mineral volumes and specific surface area, in contrast with earlier models that required mineral dissolution rates to be changed by as much as 4 orders of magnitude. The model was used in a predictive mode to evaluate penetration depth of acid fronts in a hypothetical sandstone reservoir. Crucial geochemical data were transferred to a multiphase-multicomponent reservoir simulator to allow for the viscosity of pH-sensitive polymers to change in response to water chemistry alteration during acid-polymer injection. The results show that, for a sandstone reservoir that includes minor carbonate minerals, strong acid solutions are neutralized rapidly. Even after the injection of these solutions for 1 year, acid conditions do not penetrate beyond 15 m into the reservoir. The injection of a pH-sensitive polymer with acid improves conformance in the presence of high-permeability (thief) zones as shown in three-dimensional (3D) simulations.