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Heterogeneity is a significant feature of many mature oilfields after polymer flooding, which presents great challenges for further enhanced oil recovery (EOR). The displacing fluid after polymer flooding should have the dual effects of improving the swept volume and increasing oil displacement efficiency. At present, alkali−surfactant−polymer (ASP) flooding is an important approach for further EOR after polymer flooding in the Daqing Oilfield. Preformed particle gel (PPG) is a new type of chemical agent with a powerful ability to deform and pass through the pore throat. Here, a series of experiments were carried out to investigate the profile control of PPG/ASP mixed solutions in heterogeneous reservoirs. The results show that, with respect to profile adjustment and EOR after polymer flooding, PPG/ASP mixed solutions are better than ASP-only solutions. Regarding PPG/ASP mixed solutions, PPG and hydrolyzed polyacrylamide (HPAM) could block the reservoir preferential fluid flow pathways via their properties of easy deformation and high viscosity in order to achieve the purpose of improving the swept volume; at the same time, Na 2 CO 3 and petroleum sulfonate could reduce oil−water interfacial tension so as to increase oil displacement efficiency. Besides, compared with ASP-only solutions, PPG/ASP mixed solutions have greater resistance and residual resistance coefficients, higher viscosity, and better flow control stability. Oil recovery enhanced by using PPG/ASP mixed solutions after polymer flooding boasts 3.4% more original oil in place (OOIP) when compared to ASP-only solutions, and the consumption of chemical agents is reduced by 15.8%. Furthermore, the proportion and characteristics of microscopic residual oil distribution after different flooding systems were investigated. The results are consistent with the core flooding experiment and confirm that when combined, PPG and ASP have a synergistic effect on profile control after polymer flooding in heterogeneous reservoirs.

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After tertiary recovery from the oilfields, improving the production of the remaining hydrocarbon is always challenging. To significantly improve oil recovery, a heterogeneous composite flooding system has been developed with preformed particle gels (PPG) and polymers according to the technical approach of plugging and flooding combination. In addition, an oil saturation monitoring device and a large-scale 3D physical model were designed to better evaluate the performance of the technique. The evaluation results show that the viscosity, stability, and elasticity of the heterogeneous composite flooding system are better than the single polymer system. In addition, both systems exhibit pseudoplastic fluid characteristics and follow the principle of shear thinning. The results of seepage experiments showed that PPG migrates alternately in porous media in the manner of “piling plugging-pressure increasing-deformation migration”. The heterogeneous composite system can migrate to the depths of the oil layer, which improves the injection profile. In the visualization experiment, the heterogeneous composite system preferentially flowed into the high-permeability layer, which increased the seepage resistance and forced the subsequent fluid to flow into the medium and low permeability layers. The average saturation of the high, medium, and low permeability layers decreased by 4.74%, 9.51%, and 17.12%, respectively, and the recovery factor was further improved by 13.56% after the polymer flooding.