Molecular mechanisms of asphaltene adsorption inhibition via interfacial thermodynamics and surface roughness control using green nanocomposite

The precipitation and deposition of asphaltenes in oil reservoirs severely impair production efficiency by reducing permeability and clogging pore networks. Developing effective, environmentally sustainable inhibition strategies is therefore critical for flow assurance and enhanced oil recovery. This study investigates a novel green nanocomposite (NCs) of ZnO/SiO2/xanthan-gum/walnut-shell composition for controlling asphaltene adsorption using Iranian heavy crude and 99.99% CO2 at 89 °C and pressures up to 33 MPa. An integrated approach combining ultraviolet-visible (UV-Vis) spectrophotometry, high-pressure CO2-crude oil interfacial tension (IFT) measurement, and atomic force microscopy (AFM) surface topography mapping was employed to evaluate the NCs performance under simulated reservoir conditions (89 °C, up to 33 MPa). This study reports the first direct, quantitative correlation between NCs-induced surface smoothening (via AFM) and macroscopic permeability retention in native-state crude systems under reservoir conditions, a linkage not previously quantified. Adsorption behavior was modeled using Langmuir and Freundlich isotherms, and core flooding experiments were used to assess permeability preservation. The NCs demonstrated superior asphaltene inhibition. Adsorption isotherm analysis confirmed a monolayer chemisorption process, best described by the Langmuir model (R2 = 0.9951), suggesting surface-limited monolayer adsorption with a high capacity (Qm = 434.78 mg/g), exceeding conventional adsorbents like silica. IFT measurements revealed that the NCs significantly modified the pressure-dependent interfacial behavior, enhancing the IFT slope in the high-pressure regime (> 30 MPa) by 38.5% compared to the untreated system. AFM topographic analysis quantitatively confirmed a dramatic reduction in surface roughness on sandstone substrates: average roughness (Ra) decreased by ~ 21.66%, root mean square roughness (Rq) by ~ 40.23%, and peak-to-valley height (Rt) by ~ 95.08%. Core flooding tests corroborated these nanoscale findings, showing substantial permeability and porosity preservation in NCs-treated cores. The results conclusively demonstrate that the NCs effectively inhibits asphaltene deposition through three synergistic mechanisms: interfacial thermodynamics modification, high-capacity monolayer adsorption, and nanoscale surface smoothening. The key novelty of this work lies in establishing a direct, quantitative correlation between NCs-mediated surface roughness reduction (AFM) and macroscale permeability preservation, a link not previously documented. This study provides a sustainable, high-performance solution for managing asphaltene-induced formation damage in depleting oil reservoirs.