Experimental Study on Entry Profile Reversal Characteristics in Composite Heterogeneous Multi-layers Reservoirs

The entry profile reversal (EPR) phenomenon is widely observed during polymer flooding in real multi-layer heterogeneous reservoirs, directly impacting ultimate recovery efficiency. First, polymer flooding experiments were conducted using three-layer heterogeneous parallel core models, summarizing the characteristics of profile reversal in multi-layer models compared to conventional dual-tube parallel models. Subsequently, the influence of varying degrees of heterogeneity in multi-layer reservoirs on profile reversal and development effectiveness was investigated. Finally, artificial cementation models were used to compare differences in profile reversal and polymer flooding performance between intra-layer and inter-layer heterogeneous reservoirs, with development recommendations proposed for multi-layer reservoirs based on the research results. The results indicate that, profile reversal in multi-layer reservoirs follows a “sequential activation” pattern, where low-permeability layers delay reversal timing in medium-permeability layers, enhancing polymer flooding recovery by 1.78%; Stronger heterogeneity leads to earlier reversal timing and reduced reversal magnitude in medium-permeability layers, with the permeability variation coefficient threshold (0.77–1.01) marking the failure of low-permeability layers’ delaying effect; Compared to inter-layer heterogeneous reservoirs, intra-layer heterogeneous reservoirs exhibit earlier profile reversal, faster reversal velocity, and poorer polymer flooding performance. This study provides references for predicting profile reversal and formulating development strategies in multi-layer heterogeneous reservoirs.