Experimental Investigation of Preformed Particle Gel and Alkali-Surfactant-Polymer Composite System for Enhanced Oil Recovery in Heterogeneous Reservoirs

Heterogeneity is a significant feature of the reservoirs after polymer flooding, resulting in challenges for further enhanced oil recovery (EOR) in heterogeneous reservoirs. In order to further improve oil recovery in the reservoirs after polymer flooding, a novel EOR system (ASP-PPG composite system) was developed using preformed particle gel (PPG) and alkali-surfactant-polymer system (ASP system). We designed an oil saturation monitoring device and a large-scale 3D heterogeneous physical model to evaluate the performance of the system. The performance of the system and the ASP system were tested. Based on the testing results, the fluid migration patterns and enhanced oil recovery mechanisms of the ASP-PPG system in an actual heterogeneous reservoir were investigated using the oil saturation monitoring device and the 3D physical model. Experimental results indicate that the ASP-PPG system has a higher viscosity and better profile control ability than the ASP system. Additionally, the interfacial tension can be maintained at a low level, around 10⁻³ mN/m. Flooding experiments using the three-dimensional heterogeneous physical model demonstrated the excellent elastic deformation ability of PPG, which can dynamically block the large pores that formed after the polymer flooding and effectively improve the heterogeneity of reservoirs. After injecting the ASP-PPG system, the recovery factor of the model increased by 15.8%. Specifically, the sweep coefficient of high, medium, and low permeability layers increased by 4.36%, 19.6%, and 37.55%, respectively. Moreover, the oil displacement efficiency increased by 7.4%, 14.4%, and 17.9%, respectively. These results highlight the synergistic effect of combining PPG and ASP systems, significantly enhancing heterogeneous reservoir recovery after polymer flooding.