A Review of Miscible Zone Research in CO₂ Miscible Flooding

The formation and evolution of the miscible zone are critical to displacement efficiency in CO₂ miscible flooding. A thorough understanding of its dynamic behavior provides essential guidance for optimizing injection and production strategies, improving oil recovery, and achieving sustainable and efficient reservoir development. This paper systematically reviews relevant research advances, summarizing the formation mechanisms and characterization methods of the miscible zone, along with its migration behavior from both experimental and numerical simulation perspectives. Analysis reveals that CO₂ and crude oil achieve dynamic miscibility through multiple contacts, with the miscible zone being predominantly governed by convective-diffusive processes after its formation. Under ideal conditions, the miscible front advances uniformly in an arc-like shape. As temperature increases, the initially miscible phases may gradually separate but can reachieve miscibility upon reaching a certain temperature threshold. To further enhance the application effectiveness of CO₂ miscible flooding technology, future research should focus on accurate prediction of the minimum miscibility pressure (MMP), standardized characterization of the miscible zone, and development of effective control strategies for the miscible zone.