Abstract: Shale gas development often suffers from wellbore instability due to microfractures in the formation, posing serious challenges to drilling safety and efficiency. This study presents a functionalized graphene oxide (GO-PAA) nanomaterial, prepared by grafting hydrophilic polyacrylic acid (PAA) chains onto GO surfaces to enhance dispersion stability under high salinity, elevated temperature, and wide pH conditions. The results indicate that GO-PAA effectively resists charge-shielding effects under conditions of high salinity, elevated temperature, and a wide pH range, significantly reducing the risk of particle aggregation. Even at high salt concentrations, the zeta potential remains below −32.8 mV, demonstrating good colloidal stability. Plugging performance was evaluated using simulated core experiments. GO-PAA formed a “band-aid” like barrier on shale microfracture surfaces, reducing permeability by up to 57.53%, nearly twice that of conventional spherical nanoparticles. Scanning electron microscope (SEM) and elemental analysis confirmed the formation of a dense and uniform plugging layer. The synergistic interaction between GO’s 2D lamellar structure and the flexible polymer chains facilitated effective surface adhesion and coverage. This adsorption–adhesion plugging mechanism represents a shift from traditional bridging theories, enabling reduced material usage and improved efficiency. The findings provide theoretical and practical support for designing high-performance nanoplugging agents in water-based drilling fluids, contributing to safer and more sustainable shale gas development.