Pore-scale study of fluid transport mechanism during CO2-saturated brine injection for sequestration in carbonate aquifers

Understanding strong coupling between fluid transport and calcite dissolution during CO2 sequestration in carbonate aquifers is critical for predicting long-term storage efficiency and security. In this study, fluid transport and solid dissolution processes at the pore scale are investigated during CO2 injection into carbonate aquifers containing both fully dissolvable and partially dissolvable porous media. The dissolution patterns, reactive zones, normalized permeability (K/K0), normalized porosity (ε/ε0), and the K/K0–ε/ε0 relationship across the Péclet number (Pe = 2–8) and the Damköhler number (Da = 20–160) are discussed. Results indicate that increasing Pe expands the calcite reactive zone, which leads to a three-stage evolution in K/K0: an initial stage of slow growth, followed by rapid growth, and culminating in a stage of sharp acceleration. When ε/ε0 < 1.20, K/K0 increases with both ε/ε0 and Pe. However, lower Pe yields higher K/K0 when ε/ε0 > 1.20 due to more complete upstream dissolution. Variations in Da minimally influence reactive zones and K/K0 prior to through-going channel formation. But higher Da drives rapid permeability increases afterward, shortening reaction completion time. At ε/ε0 < 1.15, lower Da exhibits higher K/K0, reversing at ε/ε0 > 1.15. Insoluble solids accelerate early-stage K/K0 growth but constrain its upper limit. These findings elucidate the interplay between flow, reaction, and heterogeneity, providing insights for predicting long-term carbon sequestration efficacy.