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

Abstract

We report an experimental study of the behavior of CO 2 and N 2 foams in granular porous media using X-ray computed tomography. In the experiments either CO 2 or N 2 gas is forced through natural porous media initially saturated with a surfactant solution, a process known as surfactant-alternating-gas or SAG. The CO 2 was either under sub- or supercritical conditions, whereas N 2 remained under subcritical conditions at all experimental conditions. We found that CO 2 injection following a slug of surfactant can considerably reduce its mobility and promote higher liquid recovery at the experimental conditions investigated. Foaming of CO 2 builds-up a lower pressure drop over the core at both low and high pressures than N 2 . Both gases require space to develop into foam. The space is longer for N 2 (larger entrance effect) and increases with increasing gas velocity. Moreover, the ultimate liquid recovery by CO 2 foam is always lower than by N 2 foam. The possible mechanisms explaining the observed differences in foaming behavior of the two gases are discussed in detail.