Pore-scale evolutionary dynamics of intermittent flow-induced residual oil remobilization for CO2-EOR and storage synergy

Abstract

Achieving global carbon neutrality necessitates the synergistic optimization of CO2-enhanced oil recovery (CO2-EOR) and sequestration. However, the intricate multiphase flow dynamics emerging from the interplay between complex reservoir architectures and multicomponent fluid interactions remain a critical bottleneck. This study integrates in situ X-ray computed tomography (CT) with pore-scale topological correlation analysis to quantify the dynamic evolution of gas-water-oil distributions under varied injection regimes. Our results reveal that the alternating occupancy of CO2 and brine creates a dynamic pressure field, which disrupts classical capillary equilibrium. This intermittent flow thins and ruptures oil layers at narrow pore throats. Therefore, residual oil trapped in “dead-end” pores can be effectively remobilized. We quantify this mobilization through interfacial curvature evolution, demonstrating that a reduction in mean curvature serves as a robust quantitative indicator for oil connectivity enhancement. Topologically, network-like residual oil clusters exhibit high sensitivity to local pressure fluctuations, facilitating reconnection and displacement. Furthermore, we establish a definitive pore-scale trade-off: each 1% increase in CO2 storage efficiency results in a 3.80% reduction in oil recovery. Through Pareto-based multi-objective optimization, an optimal operational window—defined by a CO2 fractional flow of 0.4 and a capillary number of 3.94 × 10−7—is identified to maximize the synergy between energy production and carbon storage. These findings bridge the gap between microscopic interfacial phenomena and macroscopic engineering strategies, providing a mechanistic basis for sustainable geo-energy development.