Mobilization characterization of remaining oil by CO2 water-gas alternating after water flooding in low-permeability reservoirs

CO2 water-gas alternating (WAG) injection is an effective technique for enhancing oil recovery in low-permeability reservoirs. Following water flooding, CO2 penetrates high water-saturation throats, forming trapped gas that reduces water production while increasing oil recovery. This study employs microfluidic visualization experiments to observe fluid flow behavior and remaining oil mobilization during CO2 WAG injection in low-permeability reservoirs after water flooding. This study focuses on two models with different pore structures: matrix and fracture. It examines the evolution of remaining oil types, micro-scale displacement mechanisms, and pore-scale flow channel utilization in these models. CO2 injection reduces crude oil adhesion force and interfacial tension, disrupting oil-water equilibrium and increasing local driving pressure to mobilize remaining oil effectively. Multiple WAG cycles activate various remaining oil types and improve sweep efficiency. As WAG cycles increase, throat utilization remains consistent (8–30 μm) while oil displacement efficiency improves. This study reveals the mechanisms of CO2 WAG technology in low-permeability reservoirs, providing novel microscale insights and demonstrating its potential to optimize recovery strategies.