Experimental Study of Dense CO₂ Foam-flow Behavior in Porous Media at Elevated Pressure

by
Ji Sung Kim, MSE

University of Texas at Austin, 2003
Supervisor: Dr. William R. Rossen

Foams can improve oil recovery by reducing gas mobility and the effects of reservoir heterogeneity. However, the lack of knowledge about the complex nature of foam flow behavior in porous media prevents wider applications of foam in the petroleum industry. Recently, Osterloh and Jante (1992) found that foam flow in porous media can be divided into two regimes: a high-quality regime and a low-quality regime. In the high-quality regime, pressure gradients are nearly independent of gas superficial velocity. In the low-quality regime, pressure gradients are 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 appears to show both regimes. The existence of two foam flow regimes can be very useful to the study and modeling of foam in the petroleum applications. The purpose of this study is to investigate whether the two steady-state foam-flow regimes exist for dense CO₂ foam.

An apparatus was designed to conduct high-pressure CO₂ foam flooding experiments. Experiments were performed with a sand-pack and a fired Boise sandstone core at a back-pressure of 2000 psig and room temperature, below the critical temperature of CO₂. One additional experiment with fired Boise sandstone was conducted to investigate CO₂ foam flow above the critical temperature of CO₂. Surfactant solution and dense CO₂ were co-injected through the porous media. Neodol 25-9 surfactant at 1% concentration and the same salt concentration were used in all experiments.

The data from the sand-pack and Boise=sandstone experiments at room temperature do not show the two conventional foam-flow regimes. Instead, these experiments find a third regime related to the low-quality regime. In this regime, pressure gradients decrease with increasing liquid superficial velocity at constant gas superficial velocity at constant gas superficial velocity. The Boise-sandstone experiment above the critical temperature of CO₂ did find the two distinct foam-flow regimes, however.

Earlier theoretical work of Hirasaki and Lawson (1985) and de Vries and Wit (1990) can explain the new behavior seen in our study. A more sophisticated model combining that of Rossen and Wang (1997) with the effective viscosity of Hirasaki and Lawson predicts the behavior in this new regime. These theories are discussed in the Appendices.

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