Saturated carbon dioxide nanofluids enhanced oil recovery in carbonate reservoir cores using nuclear magnetic resonance

The wettability, fingering effect and strong heterogeneity of carbonate reservoirs lead to low oil recovery. However, carbon dioxide (CO₂) displacement is an effective method to improve oil recovery for carbonate reservoirs. Saturated CO₂ nanofluids combines the advantages of CO₂ and nanofluids, which can change the reservoir wettability and improve the sweep area to achieve the purpose of enhanced oil recovery (EOR), so it is a promising technique in petroleum industry. In this study, comparative experiments of CO₂ flooding and saturated CO₂ nanofluids flooding were carried out in carbonate reservoir cores. The nuclear magnetic resonance (NMR) instrument was used to clarify oil distribution during core flooding processes. For the CO₂ displacement experiment, the results show that viscous fingering and channeling are obvious during CO₂ flooding, the oil is mainly produced from the big pores, and the residual oil is trapped in the small pores. For the saturated CO₂ nanofluids displacement experiment, the results show that saturated CO₂ nanofluids inhibit CO₂ channeling and fingering, the oil is produced from the big pores and small pores, the residual oil is still trapped in the small pores, but the NMR signal intensity of the residual oil is significantly reduced. The final oil recovery of saturated CO₂ nanofluids displacement is higher than that of CO₂ displacement. This study provides a significant reference for EOR in carbonate reservoirs. Meanwhile, it promotes the application of nanofluids in energy exploitation and CO₂ utilization.