Tight conglomerate reservoirs exhibit strong pore-scale heterogeneity and extremely low permeability, in which spontaneous imbibition is primarily governed by capillary and viscoelastic effects. In this study, the imbibition dynamics of four representative fracturing fluid systems, including slickwater, 3% potassium chloride (KCl) brine, hydrolyzed polyacrylamide (HPAM) viscoelastic fluid, and a nanoemulsion (NE), were investigated using a temperature-controlled nuclear magnetic resonance (NMR) monitoring system. This approach enables real-time quantification of fluid uptake and pore-scale redistribution through time-resolved T2 spectral analysis. The experimental results reveal a three-stage imbibition process consisting of rapid capillary-driven uptake, viscoelastic-retarded transition, and final equilibrium. Among the four fracturing fluid systems, the nanoemulsion exhibits the lowest interfacial tension (1.72 mN/m), the strongest wettability alteration, and the highest equilibrium recovery (0.76), which is nearly 80% greater than that of slickwater. Based on these observations, a multiscale capillary–viscoelastic coupling model was developed by extending the Lucas–Washburn framework to incorporate pore-size distribution, time-dependent wettability evolution, and viscoelastic damping. The model fits the experimental data well (R2 > 0.90) and identifies viscosity as the most influential parameter controlling the imbibition rate (sensitivity = 0.78). Energy analysis further indicates that capillary energy dominates the early stage, whereas viscoelastic energy storage sustains fluid transport during the later stage. SEM observations were further used to qualitatively corroborate pore heterogeneity and pore–mineral associations, supporting the NMR-based pore-scale interpretation. This study provides a quantitative framework for describing non-Newtonian capillary flow in tight conglomerate rocks and enhances the understanding of capillary–viscoelastic interactions relevant to multiphase fluid migration.
GUO et al. (Wed,) studied this question.