Multiscale characteristics and cracking behavior in reservoir sandstone under dry-wet cycles: Insights from NMR, AE and SEM

spectrum evolves from unimodal to bimodal, suggesting enhanced the pore-scale heterogeneity. This phenomenon is accompanied by a significant reorganization of the pore structure, with the proportion of micropores decreasing from 8.09% to 0.24% and that of macropores increasing from 50.78% to 65.30%. SEM observations corroborate the multiscale degradation mechanism, revealing that early-stage damage is characterized by dissolution pits and isolated microcracks on mineral surfaces. In contrast, progressive cycling substantially weakens interparticle cementation, generates abundant debris, and promotes the coalescence of microcracks into macroscopic fractures. This integrated AE-NMR-SEM framework links pore-scale evolution to macroscopic failure processes, providing a quantitative method for precursor identification and failure-mode transition assessment in reservoir rock mass.