Development and performance evaluation of foaming agent for heavy oil development and study on oil displacement mechanism in heterogeneous micromodel

Due to their high viscoelasticity and excellent plugging ability, surfactant foam systems can mitigate the effects of heterogeneity and have emerged as a key technology in tertiary oil recovery in recent years. Moreover, achieving ultra-low oil/water interfacial tension (IFT) is critical for enhanced oil recovery (EOR), as it facilitates the deformation and mobilization of oil droplets from pores. However, conventional surfactant systems often struggle to simultaneously achieve ultra-low oil/water IFT and high foam performance. To overcome this limitation, this study developed a composite surfactant system by combining small-molecule anionic and cationic surfactants with a nonionic surfactant, enabling both ultra-low oil/water IFT and high foam performance. The compound surfactants were evaluated for IFT, emulsification performance, and foam performance within a concentration range of 1–10 mM. Based on the comprehensive evaluation results, a concentration of 4 mM was selected for further investigation in a heterogeneous micro-model oil displacement experiment to analyze its displacement behavior. The results demonstrated that at a concentration of 2 mM, the foaming agent achieved the lowest oil/water IFT of 9.834 × 10− 4 mN/m, while at 4 mM, the foam composite index reached its peak value of 12,960 mL·min. The ability to reduce IFT was found to be approximately proportional to foam performance and inversely proportional to emulsification performance. The heterogeneous micro-model oil displacement experiment demonstrated that chemical flooding increased the recovery ratio by 24% compared to water flooding, with the foam action zone exhibiting significantly enhanced displacement efficiency. The novelty of this study lies in the use of surfactants with different properties to construct a foam system with ultra-low oil/water IFT and excellent foam performance, as well as the execution of heterogeneous micro-model displacement experiments. This work provides valuable insights for the design of fracture carbonate foaming agents and future studies on EOR.