Abstract: This paper addressed the effects of hydrophobic synthesized Calcium oxide(CaO) and commercial Silicon dioxide (SiO2) nanoparticles on the inhibition of asphaltene precipitation after asphaltene adsorption on the nanoparticles surface. First, asphaltene characterization was performed with Fourier-transform infrared spectroscopy (FTIR)and its stability was analyzed with screening methods. Second, experimental and isotherm models including Langmuir and Freundlich were used to observe the effects of CaO and SiO2 nanoparticles on asphaltene adsorption. Third, CO2-oil interfacial tension (IFT) behaviors were used as a second method for surveying asphaltene adsorption in the presence of nanoparticles. Finally, natural depletion and CO2 tests were done as a source of precipitation methods. The studied crude oil was located in unstable regions from the aspect of asphaltene precipitation with colloidal instability index (CII)of 1.392. The results of asphaltene precipitations during natural depletions and Carbon dioxide tests were in good agreement with CO2-oil IFT behavior, and CaO not only adsorbed more asphaltene but also had the best application for precipitation inhibition. The Langmuir isotherm modeled the asphaltene adsorption data well in the presence of nanoparticles and CaO nanoparticles had the highest adsorption capacity. According to CO2-oil IFT behavior, two different pressure changes were seen. As pressure increased in the first region, IFT decreased due to oil swelling. In the second region, the slope became slower than the first region due to aggregation of asphaltene in the interface of two fluids. After adding nanoparticles, the IFT slope changed and became higher in comparison to the base case in the second region, which confirmed that asphaltene was adsorbed on the nanoparticles surface.
