Percolation model for permeability reduction in porous media by continuous-gas foams

Percolation modeling concepts are invoked to construct estimates of gas permeability modification as a result of the introduction of low concentration or poorly stabilizing surface-active agents in a gas injection process in porous media. The creation of a low number of quasi-stable lamellae in porous media results in an increased stationary gas saturation and is modeled as a reduction in effective connectivity of the medium. Medium connectivity impacts the minimum free gas saturation for continuity and the associated characteristic length scale strongly correlated with permeability. The complex process of in situ foam generation and propagation is modeled through a foam efficiency parameter and, ultimately, through the assertion of a roughly constant mobile gas saturation for good foaming agents. The model is shown to adequately portray literature foam relative permeability measurements with mobile gas saturation values consistent with the reported values for similar porous media systems. In the limit where gas percolation is lost, a second mode of transport involving bubble propagation is observed. The two regimes of foam transport have been observed in visualization experiments for gas injection into a brine-saturated, matched refractive index sandpack. For many processes, the dramatic decrease in gas mobility associated with propagation of lamellae is detrimental, making process design and modeling for the continuous-gas regime important.