Carbon dioxide storage combined with enhanced oil recovery (CCS-EOR) is an important approach for reducing greenhouse gas emissions. We use pore-scale imaging to help understand CO₂ storage and oil recovery during CCS-EOR at immiscible and near-miscible CO₂ injection conditions. We study in situ immiscible CO₂ flooding in an oil-wet reservoir rock at elevated temperature and pressure using X-ray micro-tomography. We observe the predicted, but hitherto unreported, three-phase wettability order in strongly oil-wet rocks, where water occupies the largest pores, oil the smallest, while CO₂ occupies pores of intermediate size. We investigate the pore occupancy, existence of CO₂ layers, recovery and CO₂ trapping in the oil-wet rock at immiscible conditions and compare to the results obtained on the same rock type under slightly more weakly oil-wet near-miscible conditions, with the same wettability order. CO₂ spreads in connected layers at near-miscible conditions, while it exists as disconnected ganglia in medium-sized pores at immiscible conditions. Hence, capillary trapping of CO₂ by oil occurs at immiscible but not at near-miscible conditions. Moreover, capillary trapping of CO₂ by water is not possible in both cases since CO₂ is more wetting to the rock than water. The oil recovery by CO₂ injection alone is reduced at immiscible conditions compared to near-miscible conditions, where low gas-oil capillary pressure improves microscopic displacement efficiency. Based on these results, to maximize the amount of oil recovered and CO₂ stored at immiscible conditions, a water-alternating-gas injection strategy is suggested, while a strategy of continuous CO₂ injection is recommended at near-miscible conditions.

二氧化碳存储与提高采油量（CCS-EOR）相结合是减少温室气体排放的重要方法。我们使用孔尺度成像来帮助了解在不混溶和几乎混溶的CO ₂注入条件下CCS-EOR过程中的CO ₂储存和油采收率。我们使用X射线显微断层扫描技术研究了在高温高压下油湿储层岩石中的原位不混溶CO ₂驱替。我们在强油湿岩石中观察到了预测的但迄今尚未报道的三相润湿性顺序，其中水占据最大的孔隙，油占据最小的孔隙，而CO ₂占据中等大小的孔隙。我们调查孔的占有率，CO _2的存在在不混溶的条件下在油-湿岩石中形成层，采收率和CO ₂捕集，并与在相同的岩石类型下在油润湿性差的情况下具有相同的润湿性顺序下，在稍弱的油-湿混溶条件下获得的结果进行比较。在接近混溶的条件下，CO ₂在连接层中扩散，而在不混溶的条件下，CO ₂在中型孔中以不连续的神经节形式存在。因此，油在毛细管中捕获CO ₂的过程是在不混溶的条件下发生的，而不是在几乎混溶的条件下发生的。而且，在两种情况下都不可能通过水毛细管捕集CO ₂，因为与水相比，CO ₂对岩石的润湿性更大。通过CO ₂采油与几乎混溶的情况相比，在不混溶的情况下，单独的喷射减少了，在这种情况下，低的油气毛细管压力提高了微观驱替效率。根据这些结果，为使在不混溶条件下的采出油量和CO _2的存储量最大化，建议采用水交替气注入策略，而在接近混溶条件下建议连续注入CO ₂。