Supercritical CO2 Foam Stability in the Presence of Oil

Foam is a field-proven technique to reduce CO2 mobility and mitigate the impacts of reservoir heterogeneity in CO2-enhanced oil recovery (CO2-EOR). However, foams are unstable and tend to break down in the presence of oil. Screening foam generation and stability in the presence of oil, at representative reservoir pressure and temperature, at core-scale is critical for successful upscaling. This study investigates the effect of oil on foam generation and stability across a range of foam qualities (fg = 0.30 to 1.0) and injection velocities (4 ft/day to 16 ft/day). Foam quality and rate scans using Bentheimer sandstone cores were conducted in presence/absence of oil (n-decane and Troll crude) at reservoir conditions (60 °C and 180 bar). Foam quality scans co-injected supercritical CO2 and foaming solutions with increasing foam quality (fg = 0.30 to 1.0) to determine the optimal foam quality (highest apparent viscosity foam). T optimal foam quality was then used in rate scans to determine the effect of injection velocity on foam strength. In addition, two separate core floods at two fixed foam qualities (fg = 0.30 and 0.70) were performed to determine the oil recovery factor during foam injection. Strong foam was generated, in both the presence and absence of oil, but oil significantly reduced foam strength. The foam apparent viscosity was reduced by ~93% (Troll crude) and ~90% (n-decane) compared to foam in the absence of oil. Increasing the surfactant concentration from 0.10 wt.% to 1.0 wt.% significantly enhanced the foam mobility control, with the apparent viscosity in the presence of oil increasing from 7.9 cP to 25.9 cP. The optimal foam quality in the presence of both oils ranged from fg = 0.60 to 0.70. Foam rate scans revealed shear-thinning rheology (foam viscosity decreased at higher flow rates), which is beneficial for maintaining field-scale injectivity. This study provides critical insights into how oil impacts supercritical CO2 foam strength, stability mechanisms, and oil recovery at reservoir conditions, crucial for field-scale implementation in CO2-EOR and CO2 storage projects.