Toward mechanistic understanding of asphaltene adsorption onto quartz surface: The roles of size, concentration, and hydrophobicity of quartz, asphaltene composition, flow condition, and aqueous phase

Abstract

The nature of asphaltene and mineralogy of reservoir rock affect the adsorption of asphaltene onto the rock surface. The basic goal of the present study is to assess the adsorption of different asphaltenes on quartz as the main mineral of sandstone formations. For this purpose, asphaltenes were separated from four crude oil samples from different Iranian oil reservoirs and their specifications were analyzed applying various methods including Fourier-transform infrared spectroscopy, elemental analysis, dynamic light scattering, and field emission scanning electron microscopy. Also, X-ray fluorescence and Brunauer–Emmett–Teller methods were carried out to analyze the quartz mineral. Adsorption experiments were performed both statically and dynamically and the effects of the water phase and hydrophobicity of quartz on the adsorption of asphaltene on the mineral were evaluated. The calculated H/C ratios of asphaltenes are in the range of 1.2–1.3, and their average particle size is between 46 and 380 nm. The results of static tests showed that asphaltenes uptake by quartz adsorbents is from 1.16 to 6.78 mg/m2. The results of this work indicated that the adsorption amount of asphaltenes on the quartz surface is directly related to the nitrogen content and polarity of asphaltene, but it is not related to the average particle diameter of asphaltenes and their aromatic nature. By double increasing the flow rate in the dynamic adsorption process, the asphaltene uptake by quartz is reduced by about 35%, which could be an indication of the physical nature of asphaltene adsorption on quartz. Finally, compared to the asphaltene uptake by quartz in the two-phase system, the uptake in the three-phase system on average shows a decrease of more than 30%, which indicates the effect of the competitive presence of water with asphaltene for the surface-active sites. Also, the uptake of asphaltene onto the quartz samples increased with increasing the initial asphaltene concentration and decreasing quartz particle sizes. The effect of wettability on asphaltene adsorption in two- and three-phase systems was investigated using hydrophilic and hydrophobic quartz nanoparticles. In both systems, the adsorption of asphaltene on hydrophobic nanoparticles was higher and the adsorption reduction in the three-phase system was calculated to be between 5 and 10%, which was very small compared to hydrophilic nanoparticles with an adsorption reduction of 30–60%. Wettability of nanoparticles compared to their specific surface area showed more importance in asphaltene adsorption.