Improvement of supercritical carbon dioxide foam performance for EOR in sandstone reservoirs: An experimental and optimization study

Carbon capture is a way of reducing CO₂ emissions by capturing and storing CO₂ in geological reservoirs, deep saline aquifers, or using it for enhanced oil recovery (EOR). EOR using CO₂ is currently one of the most successful EOR techniques. Unfortunately, gas injection techniques suffer from high gas mobility and gravity override, which decrease the macroscopic sweep efficiency and ultimately the oil recovery. Foams may tackle these issues by decreasing gas mobility and gravity override; however, CO₂ generates weak foam at its critical conditions, and most reservoirs exist at high pressures and temperatures that exceed CO₂ critical conditions. In these conditions, these issues may be tackled by the partial replacement of CO₂ with nitrogen, as mixtures of CO₂ and N₂ can produce strong foam compared to the weak foam generated by CO₂ alone. Different core flooding experiments were conducted to investigate the effect of changing the CO₂/N₂ ratio, injection rate, and foam quality on the performance of the mixed foam. The results show that the foam quality, injection rate, and CO₂/N₂ ratio must be optimized for enhanced oil recovery. It was observed that increasing N₂ content above 20% improved the foam properties; however, it did not result in higher recovery. In addition, decreasing N₂ content below 10% did not help the recovery. The optimized foam quality appears to be approximately 80% with a CO₂/N₂ ratio of 4:1 and 0.5 cc/min injection rate to obtain the highest oil recovery. This study provides an effective and simple solution for improving and optimizing the parameters for mixed foam injection under reservoir conditions, which can produce more oil and store significant quantities of CO₂ underground.