An insight into hydrogen and carbon dioxide displacement and trapping efficiencies in carbonate formations through NMR and core flooding

The complex pore structure of carbonates can influence gas storage process to different extents, depending on stored gas type. Hence, investigating gas displacement and residual trapping in such formations is crucial. Here, several CO₂ and H₂ core flooding experiments were performed using three carbonate samples. The drainage process is followed by brine imbibition to test gas residual trapping. Additionally, nuclear magnetic resonance (NMR) T₂ spectra measurements were conducted at different stages. The results show that H₂ had less displacement efficiency in carbonates compared to CO₂. The pore structure has a noticeable impact on CO₂ displacement efficiency. However, H₂ displacement efficiency is less sensitive to rock properties. The NMR-T₂ measurements show that CO₂ partially saturated medium-sized pores and almost filled all macropores during drainage. After imbibition, large pores are slightly re-saturated with brine with varying degrees compared to their initial brine saturations. H₂ shows lower residual trapping efficiency compared to CO₂.