Experimental and modeling study of foam coarsening kinetics in porous media

The geometric confinement significantly affects the foam coarsening dynamics in porous media. We present the experimental and modeling studies of coarsening-induced foam structural evolution in a porous microfluidic chip. The findings are expected to shed light on predicting the foam structure in many applications, such as foam-assisted enhanced oil recovery process and CO₂ geological sequestration. It is shown that, in porous media, small bubbles are constantly consumed by large bubbles due to inter-bubble gas diffusion until most bubbles grow to the pore or throat size. The coarsening of edge bubbles (bubbles contacting the boundary) dominates the foam coarsening process, showing a linear increase in the average area of edge bubbles with time in a steady-state growth state. A mass transfer model is proposed to fit the foam coarsening rate of edge bubbles, including critical parameters such as liquid film permeability, gas-liquid interfacial tension, the molar volume of the dispersed phase, and the polydispersity of bubble size distribution. We emphasize that, under the same experimental conditions, foams with a broader size distribution exhibits a faster coarsening rate due to higher capillary pressure differences among the bubbles as the mass transfer driving force.