Micofluidic Visualization of Oil Displacement Mechanisms by CO 2 Microbubbles

CO2-enhanced oil recovery (CO2-EOR) is a key carbon capture, utilization, and storage (CCUS) technology, delivering the dual benefits of enhanced oil recovery and CO2 geological storage. However, conventional CO2 gas flooding suffers from high gas mobility, early breakthrough, and a poor sweep efficiency. This study innovatively employed the green biodegradable surfactant alkyl polyglucoside (APG) and polymer xanthan gum (XG) to stabilize microbubbles, establishing a microbubble CO2 (MB-CO2) flooding system. The microscopic mechanisms of MB-CO2 flooding in heterogeneous porous media were systematically investigated by using a custom-built in situ visual microfluidic platform. The results reveal that MB-CO2 enhances oil recovery through three synergistic mechanisms: plugging mechanism (enabling dynamic synergistic plugging via the Jamin effect to expand sweep volume), interfacial interactions (weakening oil adhesion through wettability alteration and oleophilic interaction to promote oil stripping), and emulsification promotion (improving oil mobility via local shear and disturbance). Experimental results demonstrate a remarkable oil recovery factor of 93.64% and an extended breakthrough time of 0.734 PV for MB-CO2 flooding, substantially outperforming the results of CO2 gas flooding (45.25%) and APG-XG solution flooding (87.26%). Sector-based analysis further confirms superior recovery efficiency and uniformity across all radial directions, with effective adaptation to both high- and low-porosity zones and suppression of premature gas breakthrough. This work elucidates the multimechanistic synergy of MB-CO2 flooding and provides a theoretical and experimental foundation for its industrial application, offering significant insights for advancing CCUS deployment and fostering a sustainable energy transition.