Asphaltene deposition poses a significant threat to production efficiency by reducing permeability in hydrocarbon reservoirs. Although various nanoparticles and polymer-based inhibitors have been proposed, a quantitative multiscale framework linking nanoscale interfacial interactions to macroscopic permeability preservation under realistic reservoir conditions remains underdeveloped. This study introduces an environmentally friendly nanocomposite (KCl/SiO2/Xanthan/Eucalyptus, denoted as NCs) that was designed to inhibit asphaltene precipitation and its associated formation damage in carbonate porous media. The inhibitory mechanism was investigated through an integrated multi-technique approach combining high-pressure interfacial tension measurements between CO₂ and crude oil, atomic force microscopy, adsorption isotherm modeling, natural depletion experiments, and core flooding experiments under simulated reservoir conditions. The NCs significantly altered the CO2-oil interfacial tension profile, increasing the slope ratio in the secondary pressure region by 120%, indicating a delayed onset of asphaltene flocculation. Adsorption isotherm analysis indicated a monolayer adsorption mechanism, best described by the Langmuir model (R2 = 0.9902), with a maximum capacity of 172.41 mg/g. Atomic force microscopy topographic analysis revealed that the NCs promote a smoother deposition pattern, reducing average surface roughness (Ra) by 56.5% and root mean square roughness (Rq) by 57.9%. Core flooding tests demonstrated the macroscopic benefits, showing a 76.28% reduction in asphaltene precipitation at 4880 psi and mitigation of permeability and porosity impairment. Collectively, the results demonstrate that the green nanocomposite effectively controls asphaltene deposition through interfacial modification, strong adsorption, and nanoscale smoothing, thereby preserving the flow capacity of carbonate reservoirs. Unlike previous eucalyptus-based nanocomposite formulations, this study establishes a quantitative linkage between adsorption energetics, interfacial tension modulation, surface roughness evolution, and macroscopic permeability preservation under realistic pressure-depletion conditions.
