We present the first 1D simulations of dynamic foam displacements with a population-balance model incorporating bubble creation controlled by pressure gradient. For the first time, a population-balance model is fit to steady-state experimental data for both the three foam states (coarse foam, intermediate, and strong foam) and the two strong-foam 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, at fixed injection rates.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 limited cases examined here, foam generation occurs at roughly the same injection rate as predicted by local-steady-state theory. Because of this narrow region of finer-textured foam, fronts can be sharper than estimated from fractional-flow theory assuming a constant effective 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 affects 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.

Foam generation plays a crucial role in the use of foam for improved oil recovery, acid diversion and environmental remediation.This sandpack study extends previous work to layered media, the effect of surfactant concentration, and injection strategy, including alternating-slug (SAG) injection and pulsed injection rate and pressure.As in earlier studies, three foam states were observed: high-mobility coarse foam at low pressure gradient, low-mobility strong foam at high pressure gradient, and, in between, an intermediate state with nearly complete gas plugging. With co-injection of gas and liquid in homogeneous sandpacks, foam generation occurred at lower pressure gradient and lower gas velocity at higher liquid injection rates, higher permeability, and higher surfactant concentration. Within the plugged state, the pressure gradients required for foam propagation were remarkably high (of order 10 psi/ft) given the high permeability of the packs. In flow from lower- to higher-permeability layers, foam generation occurred at lower pressure gradient than expected in either medium by itself. However, a minimum threshold pressure gradient for foam generation was still observed when the permeability contrast was of order 5:1, contradicting theory for foam generation at a sharp permeability transition. Foam generation was observed at all pressure gradients when the permeability contrast was 20:1. With co-injection of gas and liquid into layered packs, the low-mobility zone near the transition in permeability spread downstream if pressure gradient was sufficient. During gas injection in SAG processes, a low-mobility front traveled the length of homogeneous packs and then exited. In heterogeneous packs, SAG injection gave persistent low mobility near the transition in permeability. Gas mobility in SAG processes was from 10 to 100 times higher than with co-injection of gas and liquid. Briefly raising injection pressure in steady co-injection helped trigger foam generation in layered media, but had no lasting effect in homogeneous packs. Foam was not uniform within packs, especially in the plugged state. Therefore, properties averaged over the pack do not represent a homogeneous state. Care is needed in using such data to fit mechanistic models for foam behavior. Introduction Foam can improve conformance in gas-injection improved oil recovery (Schramm, 1994; Rossen, 1996), acidizing (Smith et al., 1969; Gdanski, 1993) and environmental remediation (Hirasaki et al., 2000; Mamun et al, 2002). For all applications, foam generation is crucial to applying foam. Foam generation, however, is a complicated function of gas and water superficial velocities, pore geometry, the presence of oil, surfactant concentration, surfactant formulation, and other factors.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFoam generation plays a crucial role in the use of foam for improved oil recovery, acid diversion and environmental remediation. This sandpack study extends previous work to layered media, the effect of surfactant concentration, and injection strategy, including alternating-slug (SAG) injection and pulsed injection rate and pressure. As in earlier studies, three foam states were observed: high-mobility coarse foam at low pressure gradient, low-mobility strong foam at high pressure gradient, and, in between, an intermediate state with nearly complete gas plugging.With co-injection of gas and liquid in homogeneous sandpacks, foam generation occurred at lower pressure gradient and lower gas velocity at higher liquid injection rates, higher permeability, and higher surfactant concentration. Within the plugged state, the pressure gradients required for foam propagation were remarkably high (of order 10 psi/ft) given the high permeability of the packs.In flow from lower-to higher-permeability layers, foam generation occurred at lower pressure gradient than expected in either medium by itself. However, a minimum threshold pressure gradient for foam generation was still observed when the permeability contrast was of order 5:1, contradicting theory for foam generation at a sharp permeability transition. Foam generation was observed at all pressure gradients when the permeability contrast was 20:1. With co-injection of gas and liquid into layered packs, the low-mobility zone near the transition in permeability spread downstream if pressure gradient was sufficient.During gas injection in SAG processes, a low-mobility front traveled the length of homogeneous packs and then exited. In heterogeneous packs, SAG injection gave persistent low mobility near the transition in permeability. Gas mobility in SAG processes was from 10 to 100 times higher than with co-injection of gas and liquid.Briefly raising injection pressure in steady co-injection helped trigger foam generation in layered media, but had no lasting effect in homogeneous packs.Foam was not uniform within packs, especially in the plugged state. Therefore, properties averaged over the pack do not represent a homogeneous state. Care is needed in using such data to fit mechanistic models for foam behavior.