Steady-state flow behavior of CO2 foam

Foams can improve oil recovery by reducing gas mobility and the effects of reservoir heterogeneity. Numerous studies report that foam flow in porous media comprises two regimes. In the "high-quality regime," pressure gradient is nearly independent of gas superficial velocity. In the "low-quality regime," pressure gradient is nearly independent of liquid superficial velocity. Previous published data from CO2 foam studies lie either in the high- or low-quality regime, but no single study shows both regimes. Delineating the two foam-flow regimes is essential to modeling and predicting the behavior of CO2 foam in petroleum applications. Experiments were performed with a sandpack and fired Berea and Boise sandstone cores at a backpressure of 1500 or 2000 psig, above and below the critical temperature of CO2 The data from the sandpack, Berea, and Boise sandstone experiments at room temperature do not show the two conventional foam-flow regimes. Instead, these experiments find a third regime evidently related to the low-quality regime. This same behavior was observed in the sandpack above the critical temperature of CO2 In this new regime, pressure gradient decreases with increasing liquid superficial velocity at constant gas superficial velocity. The Boise sandstone experiment above the critical temperature of CO2 did find the two conventional foam-flow regimes, however. No single experimental factor appears to explain the difference in results. Earlier theoretical work of Hirasaki and Lawson and de Vries and Wit can partially explain the flow regime seen in our study. A model combining a bundle-of-tubes approach with the effective-viscosity function of Hirasaki and Lawson predicts the behavior in this new regime.