Foam Flooding in a Heterogeneous Porous Medium

The impact of heterogeneity on the flow behavior of CO₂ foam in the presence of crude oil is investigated in a complex, heterogeneous porous medium. A microfluidic device is fabricated featuring low and high permeability regions using a sequential photolithography technique. Two types of CO₂ foams are used as the injectant: (i) foam stabilized with surfactants and (ii) foam stabilized with a blend of silica nanoparticles (Si NPs) and surfactants. High-resolution images of the medium during displacement experiments reveal a phase separation between the high versus low permeability regions; foam sweeps the high permeability regions, whereas the surfactant solution, along with few gas bubbles, appears to invade the low permeability region. The gains in recovery from the low-permeability region are attributed to the resistance to flow due to a relatively high apparent viscosity of foam in the high-permeability region and the resulting diversion of flow into the low-permeability region. The enhanced stability of foams stabilized with Si NPs appears to reduce the phase separation between the two regions, which contributes to an additional recovery gain from the low-permeability region.