Stability and texture of CO2/N2 foam in sandstone

In this study, oil-free steady-state foam flooding experiments were performed in a sandstone core above the supercritical conditions of CO2 using two different surfactants - fluorosurfactant FS-51 and alpha-olefin-sulfonate (AOS). Effect of addition of N-2 to sc-CO2-foam in different proportions on stability and structure of CO2/N-2 was investigated with the two different surfactants. Co-injection of all three fluids - surfactant, CO2 and N-2 was performed and pressure drop (Delta P) data across the core was recorded and foam images were captured through a visual cell and analyzed using 'ImageJ' image analysis software. Interfacial tension experiments were also performed at same pressure and temperature conditions as foam-flooding experiments to determine the critical micelle concentration (CMC) of the two surfactants. The surfactants were injected above their CMC's during foam-flooding experiments. Results from the foam-flooding experiments showed improvement in foam strength as N-2 is added to CO2 above its supercritical conditions. The improvement in foam strength was evident by increase in steady-state pressure drop (Delta P) across the core. Analysis of captured foam images also provided evidence of increasing foam strength as the circularity of foam bubbles was significantly enhanced with addition of N-2. This study aims to provide a solution to the problem of weakening of sc-CO2-foam. The number of CO2-EOR projects around the world is increasing in lieu with the need of CO2 sequestration. The results from this study provide a safe and effective method to improve CO2-foam at high pressure and temperature reservoir conditions. The results from this study could develop CO2-foam EOR potential and help in keeping as much as CO2 below the ground.