Studies of Foam Generation in Porous Media
In steady gas-liquid flow in homogeneous porous media with surfactant present, there is often observed a critical injection velocity or pressure gradient (Ñpmin) at which “weak” or “coarse” foam is abruptly converted into “strong foam,” with a reduction of one to two orders of magnitude in total mobility. This transition is commonly called “foam generation.” For bead- and sandpacks, Ñpmin scales like (1/k), where k is permeability, over 2 1/2 orders of magnitude in k; for consolidated media, the relation is more complex. For dense-CO2 foam, Ñpmin exists but can be less than 1 psi/ft. If pressure drop, rather than flow rates, is fixed, one observes an unstable regime between stable “strong” and “coarse” foam regimes; in the unstable regime Ñp is nonuniform in space or variable in time.