Comparative Study of CO₂and N₂Foams in Porous Media at Low and High Pressure−Temperatures

Abstract

We report an experimental study of the behavior of CO2 and N2 foams in granular porous media using X-ray computed tomography. In the experiments either CO2 or N2 gas is forced through natural porous media initially saturated with a surfactant solution, a process known as surfactant-alternating-gas or SAG. The CO2 was either under sub- or supercritical conditions, whereas N2 remained under subcritical conditions at all experimental conditions. We found that CO2 injection following a slug of surfactant can considerably reduce its mobility and promote higher liquid recovery at the experimental conditions investigated. Foaming of CO2 builds-up a lower pressure drop over the core at both low and high pressures than N2. Both gases require space to develop into foam. The space is longer for N2 (larger entrance effect) and increases with increasing gas velocity. Moreover, the ultimate liquid recovery by CO2 foam is always lower than by N2 foam. The possible mechanisms explaining the observed differences in foaming behavior of the two gases are discussed in detail.

Small Core Flood Experiments for Foam EOR - Screening Surfactant Applications

“…Core flood studies have been carried out using many different types of cores (Kristiansen and Holt, 1992;Mannhardt et al 2000;Kovscek and Bertin, 2003;Zitha et al 2006;Nguyen et al, 2009;Farajzadeh et al, 2009Farajzadeh et al, , 2010, sand packs (Khatib et al 1988;Osterloh and Jante, 1992;Apaydin and Kovscek, 2001;Ma et al 2013) and bead packs (Khatib et al 1988;Falls et al 1989;Aronson et al 1994). These tests have been very useful in providing information on a wide range of aspects of foam behavior, from the effect of surfactant type and concentration, to the interaction of the foam with oil, to foam flow properties such as apparent viscosity and mobility control.…”

“…The information from these core flood tests can also be fed back into the foam models (Ma et al, 2013;Boeije and Rossen, 2013;Ma et al 2014). The cores used in these tests typically, but not always (Moradi-Araghi et al, 1997;Nguyen et al, 2009;Farajzadeh et al, 2009), have diameters of at least 3.5 cm, with lengths of 30 cm and above, and these larger pore volume systems have the advantage that any small heterogeneities in the rock have no significant effect on the foam behavior.…”

A 2D Model for the Effect of Gas Diffusion on Mobility of Foam for EOR

“…A number of laboratory studies find that CO 2 foams have greater mobility that N 2 foams -in the jargon of foam EOR, the CO 2 foams are "weaker" (Kuhlman, 1990;Chou, 1991;Kibodeaux, 1997;Farajzadeh et al, 2009) A direct, conclusive comparison is difficult, because a surfactant optimized for one gas may not be optimal for another. If CO 2 foams are inherently weaker, then this could mean that the bubbles are larger, though part of the difference could reflect smaller surface tension of CO 2 against surfactant solution (Rossen, 1996;Chaubert et al, 2012), and the consequent reduced capillary resistance to flow.…”

“…There are numerous differences between CO 2 and N 2 foams: greater solubility of CO 2 in surfactant solution; faster diffusion of CO 2 through lamellae (Farajzadeh et al, 2009); lower pH with CO 2 foam; lower surface tension of supercritical CO 2 against the lamella (Rossen, 1996;Chaubert et al, 2012); different ionic strength because of dissolved HCO 3 in the aqueous phase of CO 2 foam; greater density and viscosity of the nonaqueous phase with supercritical CO 2 ; different stability because of different Hamaker constant across the lamella (Kibodeaux, 1997), etc. In particular, the faster diffusion of CO 2 through lamellae is cited as a possible cause of this difference between CO 2 and N 2 foam (Farajzadeh et al, 2009).…”

“…In particular, the faster diffusion of CO 2 through lamellae is cited as a possible cause of this difference between CO 2 and N 2 foam (Farajzadeh et al, 2009). …”