Enhancing Radial Displacement Efficiency of Non‐Newtonian Fluids via Flow Rate Control

Many subsurface engineering applications involve radial injection of non‐Newtonian fluids into fractured media, where the displacement efficiency of injected fluids profoundly impacts the injection performance. Despite its importance, how to enhance radial displacement efficiency of non‐Newtonian fluids in rough fractures remains rarely reported. Here, by conducting visualization experiments of shear‐thinning fluids radially displacing silicone oil in a rough fracture, we report a novel transition in displacement patterns from capillary fingering to compact displacement (CD) to viscous fingering with increasing injection rate, which differs from conventional expectations for Newtonian fluids. This transition induces a non‐monotonic variation in displacement efficiency, thereby enabling potential control of displacement performance. We further propose theoretical models to predict the transition and identify the optimal range of flow rate for maximizing displacement efficiency, with model predictions showing good agreement with experimental observations. This work provides guidance for predicting and enhancing displacement efficiency in engineering operations involving shear‐thinning fluids.