Microfluidic investigation of CO₂ foam flow in a heterogeneous porous medium.

Abstract

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 (<i>R</i>_g), revealing that increasing <i>R</i>_g led to a higher gas areal fraction (<i>F</i>_g), increased gas trapping, and reduced foam velocity (<i>V̄</i>_f) and texture (<i>n</i>_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.