Effect of water solubility on carbon dioxide foam flow in porous media: An X-ray computed tomography study

Carbon dioxide (CO2) has found wide application in the water-alternating-foam (WAF) processes for enhanced oil recovery (EOR), but few research works have been reported concerning the effect of water solubility on the CO2 foam rheology in a porous medium. In this paper, an X-ray computed tomography (CT) study is carried out to investigate CO2 foam flow in a consolidated Bentheimer sandstone core saturated with surfactant solution under different system pressures. As a contrast gas with much lower solubility, nitrogen foam flow is also investigated to show the essence of gas solubility effects. Careful considerations were made on the selection of contrast gases, surfactant, and experimental procedures to focus on the effect of water solubility of the gas on foam rheology in porous media. It is observed from the experiments that CO2 foam has lower pressure loss and clearly suppressed entrance effect. With the increment of system pressure, the liquid saturation increases and the pressure loss decreases significantly for CO2 foam flow in the sample core, while little change can be observed for N-2 foam flow. It can be concluded that water solubility is one of the important influential factors for CO2 foam rheology in porous media.