In CO2 projects for enhanced oil recovery (EOR) a critical factor is possible early CO2 breakthrough and consequently poor sweep efficiency. Injection of foam can block and divert CO2 which may improve sweep efficiency. Large changes in physical properties of CO2 with temperature and pressure might affect CO2-foam performance under various reservoir conditions. Recently, we have focused on understanding supercritical CO2-foam properties and this paper describes the importance of supercritical CO2 density on CO2-foam performance in outcrop Berea sandstone core material. Foam flooding experiments were conducted in sandstone core material at different pressures from 30 to 280 bar and at temperatures of 50 and 90°C using an AOSC14/16 surfactant. Results showed high foam strengths at low CO2 density. In fact, the strongest supercritical CO2-foam was generated at the lowest supercritical CO2 density tested, quite comparable to foam strength obtained with gaseous CO2. Only reduced foam strengths were found with dense supercritical CO2 (MRF 3-11). Foam generation was studied with both equilibrated and non-equilibrated fluids. Previously, we showed that CO2-foam stability and blocking ability were strongly reduced when mass transfer occured. In this study delay in foam strength build-up was observed with non-equilibrated fluids. In addition, visual observations of the foam texture indicated larger bubbles. Compared to N2-foams at similar conditions CO2-foams were weaker and showed coarser foam structure.
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