Basalt-hosted CO₂ mineralization is a promising pathway for permanent carbon storage, but injection rate selection must balance storage efficiency and hydrogeological safety. Taking the Pudong basalt formation as the target, this study established a two-dimensional coupled reactive transport model based on borehole stratigraphy and formation physical parameters. Carbonated water injection was simulated under a confining pressure of 6 MPa at injection rates of 2.5, 5, and 10 m/s. The results show that the mineralized CO₂ storage amount increased rapidly during the middle stage and approached equilibrium after approximately 300 d. The 5 m/s case achieved the highest storage amount, while the 2.5 and 10 m/s cases were 11.66% and 17.53% lower, respectively. Secondary minerals were mainly enriched in the target reservoir, baserock layer, and outlet region, causing outlet precipitation and local permeability reduction. This structure evolution further affected pore water pressure, with late-stage pressure rebounds of 17.65% and 15.03% in the 5 and 2.5 m/s cases, suggesting that injection optimization should balance mineralization efficiency with pressure buildup and related geo-disaster risks.