TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn steady gas-liquid flow in homogeneous porous media with surfactant present, there is often observed a critical injection velocity or pressure gradient ∇p min 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: i.e., "foam generation." Earlier research on foam generation is extended here with extensive data for a variety of porous media, permeabilities, gases (N 2 and CO 2 ), surfactants, and temperatures. For bead-and sandpacks, ∇p min scales like (1/k), where k is permeability, over 2½ orders of magnitude in k; for consolidated media, the relation is more complex. For dense-CO 2 foam, ∇p min 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 ∇p is nonuniform in space or variable in time. Results are interpreted in terms of the theory of foam mobilization at a critical pressure gradient.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWe present the first 1D simulations of dynamic foam displacements with a new population-balance model incorporating bubble creation controlled by pressure gradient. For the first time, a population-balance model is fit to steadystate experimental data for both the three foam states (coarse foam, intermediate state, and strong foam) and the two strongfoam regimes (low-quality and high-quality) observed in laboratory studies. Simulations confirm the stability of the coarse-foam and strong-foam states to small perturbations, and the instability of the intermediate state.In dynamic displacements, the model shows foam generation as injection rates increase, or as liquid fraction of injected fluids increases, in agreement with laboratory observations.When coarse foam is created instead of strong foam, there is a narrow region of finer foam predicted near the gas displacement front. This region appears to play a role in foam generation. However, in the cases examined, foam generation occurs at roughly the same injection rate as predicted by localsteady-state theory. Because of this narrow region of finertextured foam, fronts can be sharper than estimated from fractional-flow theory assuming a constant gas viscosity at its steady-state value behind the displacement front.If a strong foam forms in the low-quality-regime, the kinetics of foam generation and destruction affect the length of the entrance region in which foam forms. Therefore, the length of the entrance region can be used to calibrate the kinetic parameters in the model. The displacement front and the bank behind it, however, are essentially what one would have predicted from local-steady-state modeling. The complexities of population-balance modeling are not necessary, if it is known that strong foam will be created.

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