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Elucidating the underlying chemo-mechanical coupling mechanisms of acid-supercritical carbon dioxide (scCO2) reactions in shale reservoirs is essential for advancing the efficacy and safety of CO2 geo-storage and enhanced oil recovery (EOR) techniques. Multi-scale experiments-including X-ray diffraction (XRD), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), atomic force microscopy (AFM), and nanoindentation-were used to characterize changes in mineralogy, pore structure, and mechanical properties under hydrochloric acid (HCl) pretreatment, followed by scCO2 exposure. Results demonstrate that acid pretreatment acts as an efficient method to dissolve carbonate minerals, effectively boosting secondary porosity and scCO2 accessibility. Subsequent exposure to scCO2 further modifies the mineral composition and induces a marked enhancement in pore-fracture connectivity, as revealed by advanced imaging and topographical analysis. The synergistic effect of acid and scCO2, validated by nanoindentation and NMR, leads to considerable mechanical softening and superior hydrocarbon displacement efficiency. These findings establish the synergy between acid and scCO2 in dynamically reshaping the shale pore-fracture system, thereby simultaneously enhancing hydrocarbon recovery and long-term CO2 storage. This integrated approach offers a novel paradigm for optimizing reservoir stimulation within carbon capture, utilization, and storage CCUS frameworks.