CO₂-rock wettability is a key parameter which governs CO₂ trapping capacities and containment security in the context of CO₂ geo-sequestration schemes. However, significant uncertainties still exist in terms of predicting CO₂ rock wettability at true reservoir conditions. This study thus reports on wettability measurements via independent Nuclear Magnetic Resonance (NMR) experiments on sandstone (CO₂–brine systems) to quantify Wettability Indices (WI) using the United States Bureau of Mines (USBM) scale. The results show that CO₂ (either molecularly dissolved or as a separate supercritical phase) significantly reduced the hydrophilicity of the sandstone from strongly water-wet (WI ≈ 1) to weakly water-wet (WI = 0.26), and associated with that the water-wetness of the rock for the two-phase systems. This was caused by additional protonation of surface silanol groups on the quartz, induced by carbonic acid. Capillary pressure and relative permeability curves and residual CO₂ saturation were also measured; these results were compared with literature data, and general consistency was found. NMR T₂ distribution measurements also demonstrated preferential water displacement in large pores (r > 1 µm) following scCO₂ flooding, while no change was observed for smaller pores (r < 1 µm). These insights add confidence to the assessments of CO₂-rock wettability and therefore reduce project risk. This work thus aids in the implementation of large-scale CO₂ sequestration.

在CO ₂地质封存方案的背景下，CO ₂岩石润湿性是控制CO ₂捕集能力和密封安全的关键参数。然而，在预测真实储层条件下的CO ₂岩石润湿性方面仍然存在很大的不确定性。因此，本研究报告了通过对砂岩（CO _{2 -}盐水系统）进行独立核磁共振 (NMR) 实验的润湿性测量，以使用美国矿业局 (USBM) 标度量化润湿性指数 (WI)。结果表明，CO ₂（分子溶解或作为单独的超临界相）显着降低了砂岩的亲水性，从强水湿性（WI ≈ 1）到弱水湿性（WI = 0.26），并与岩石的水湿性相关对于两相系统。这是由碳酸引起的石英表面硅烷醇基团的额外质子化引起的。还测量了毛细管压力和相对渗透率曲线以及残余 CO ₂饱和度；将这些结果与文献数据进行比较，发现总体一致性。NMR T ₂分布测量也证明了在scCO ₂之后大孔隙 ( r > 1 µm) 中的优先水置换水淹，而较小的孔隙（r < 1 µm）没有观察到变化。这些见解增加了对 CO ₂岩石润湿性评估的信心，从而降低了项目风险。因此，这项工作有助于实施大规模的 CO ₂封存。