Dynamic characterization of residual oil during long-term waterflooding experiments in heterogeneous porous structures

Abstract

To improve the understanding of trapping and mobilization mechanism during multiphase flow in porous media, long-term waterflooding experiments have been performed to capture the water–oil displacement behaviors in sandstone cores with different permeability and porosity. The residual oil is therefore categorized based on force analysis and morphological characteristics. The critical values for categorization are determined by measuring differences using statistical evaluation. Simplified models of five types of residual oil are established and the dynamic variations of types and volumes of residual oil are characterized during the long-term waterflooding in the sandstone cores. The results indicate that the pore structure heterogeneity impacts the force balance and morphology of residual oil, leading to various dominant types in the sandstone cores with different permeability. Moreover, for effective mobilization of the residual oil, different strategies of enhanced oil recovery are designed controlling the force balance of residual oil. The strategies for oil mobilization are validated by the dynamic pore network modeling, and the enhanced oil recovery is up to 28 %. This study provides a new classification method of residual oil and corresponding mobilization strategies from the perspective of force balance and morphology, which is vital to enhance oil recovery in the high/ultra-high water-cut stage of the oil reservoirs.