Microfluidic investigation of CO₂ foam flow in a heterogeneous porous medium

CO₂ foam has emerged as a promising alternative to CO₂ gas for mobility control in enhanced oil recovery (EOR) applications, yet the pore-scale dynamics and mechanisms governing foam flow and oil displacement in heterogeneous porous media remain relatively underexplored. This study investigates the pore-scale behavior of CO₂ foam flow and its efficacy for EOR in a microfluidic heterogeneous porous medium under ambient conditions. The microfluidic device, composed of parallel high- and low-permeable regions with a permeability ratio of 5.8, enabled direct visualization of foam generation, propagation, and oil displacement dynamics. A flow-focusing geometry was used to produce stable foam bubbles ranging from 30-270 μm, with size and texture governed by gas pressure and liquid flow rates. The foam morphology and transport characteristics were further analyzed as functions of the gas injection ratio (R_g), revealing that increasing R_g led to a higher gas areal fraction (F_g), increased gas trapping, and reduced foam velocity (V̄_f) and texture (n_f). Oil displacement experiments using SDS solution, CO₂ gas, and CO₂ foam showed distinct differences in performance. SDS solution and CO₂ foam formed relatively stable displacement fronts in the high-permeable zone, while CO₂ gas exhibited severe viscous fingering and early breakthrough. Foam flooding achieved significantly higher oil recovery (up to 100%) at faster rates compared to gas injection, owing to foam-induced pore blocking and vertical flow diversion into the low-permeable zone. These findings provide insights for optimizing foam-based EOR processes and highlight the value of microfluidics for resolving multiphase transport phenomena at the pore scale.