Carbonated water flooding can enhance oil recovery from low-permeability sandstone reservoirs while supporting CO2 geological sequestration; however, the coupled effects of carbonated water–rock interactions on pore-scale fluid redistribution remain unclear. This study used online nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI), and mineralogical analysis to evaluate wettability-related water redistribution, mineralogical alteration, and oil mobilization in low-permeability sandstone cores exposed to carbonated water for 0, 5, 10, and 15 days, followed by immiscible CO2 flooding. With increasing exposure duration, NMR-derived water saturation increased from 0.490 to 0.571, indicating an apparent increase in pore-scale water affinity under the same saturation protocol. XRD results showed carbonate and clay/zeolite-related mineral alteration, including calcite falling below the detection or quantification limit and marked decreases in chlorite and laumontite, which were associated with modified pore-wall properties and improved water-phase access. During subsequent immiscible CO2 flooding, oil was preferentially mobilized from well-connected migration pores, while carbonated water treatment enhanced oil recovery from capillary-controlled percolation pores. The overall recovery factor increased by 2.8 percentage points, reaching 53.8% after 15 days of treatment. These results indicate that carbonated water improves CO2 flooding performance through coupled mineral alteration, pore-connectivity modification, wettability-related water redistribution, and multi-scale oil mobilization. The study provides NMR-based pore-scale evidence for interpreting carbonated water-assisted CO2 utilization and enhanced oil recovery.
Zhang et al. (Tue,) studied this question.
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