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In the development of tight gas reservoirs, effective flowback of fracturing fluids is crucial for enhancing production. However, water blocking damage caused by fluid retention significantly affects reservoir performance. This study utilizes nuclear magnetic resonance (NMR) T2 and T1–T2 techniques to analyze water blocking damage during flowback, aiming to characterize fluid retention and the degree of water blocking damage. Reservoirs are classified into Type I, Type II, and Type III, based on the physical properties, pore-throat structure, and mineral composition of core. By integrating high-pressure mercury intrusion with NMR T2 spectra, pores are categorized into macropores, mesopores, and micropores. The results indicate that micropores and mesopores are primary regions for fracturing fluid retention. As the flowback pressure differential increases, water blocking damage decreases, with Type I cores exhibiting lower water blocking damage compared to Type II and Type III cores. Furthermore, the integration of NMR T2 and T1–T2 techniques enabled the establishment of distribution and occurrence charts of hydrogen-containing substances (hydrogen water, bound fluid, and free fluid) in three types of reservoirs. The T1–T2 spectra visualize pore development and fluid retention. During flowback, significant signal changes in bound water region indicate less retained fluid. The macropores have the lowest water blocking (<90%), while mesopores and micropores exceeds 90%. After flowback, mesopores exhibit most significant changes, while micropores have highest degree of water blocking damage, potentially resulting in long-term or permanent water blocking damage. This study investigates the mechanisms of fluid retention and water blocking across pore scales, providing a scientific basis for optimizing fracturing flowback.