Mechanisms and Controlling Factors of Displacement-Front Evolution during Chemical Flooding in High Water-Cut Reservoirs

To address the short peak-production period and limited incremental recovery commonly encountered during chemical flooding of high water-cut reservoirs, this study investigates the dynamic evolution of displacement fronts and their controlling factors through laboratory experiments and numerical simulation. Two-dimensional plate flooding experiments were first conducted to characterize the evolution of the oil bank in homogeneous and heterogeneous reservoirs, revealing a four-stage process of formation, enrichment, mobilization, and residual depletion. Based on water-cut behavior, the flooding process was further classified into early-response, peak-response, and late-response stages. A three-dimensional heterogeneous reservoir model was subsequently developed to quantify the spatiotemporal evolution of the pressure, oil-bank, and chemical-agent fronts. The results show a clear displacement-front sequence, with the pressure front leading, the oil bank occupying the intermediate zone, and the chemical-agent front trailing behind. Sensitivity analyses demonstrate that the flooding system, chemical concentration, and slug size significantly influence oil-bank development. Compared with polymer flooding and polymer-surfactant flooding, the heterogeneous flooding system increases the maximum oil-bank magnitude by 72% and 43%, respectively. Higher chemical concentrations promote oil-bank enrichment, although the incremental benefit gradually diminishes. In addition, a critical slug size of approximately 0.4 PV is identified, beyond which further increases yield limited improvement.