Asphaltene adsorption on clays and crude oil reservoir rocks

Abstract

The adsorption of asphaltene on different clay minerals (kaolinite, illite, montmorillonite) and mineral oil reservoir rocks was studied. In toluene solution, specific adsorption was observed on kaolinite and a decrease in adsorption was found in the order illite-montmorillonite. In toluene/n-heptane mixtures a two-stage isotherm was recorded on the surface of the adsorbents. Surface modification by the adsorption of asphaltenes was characterized by a variety of structure-probing methods such as N 2-adsorption, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS) measurements, and FTIR spectroscopy. The hydrophobizing effect of asphaltene on clays was also checked by immersion microcalorimetry. According to XRD studies, no intercalation of asphaltene occurs in toluene and toluene/n-heptane mixture on montmorillonites. SAXS scattering curves measured on kaolinite samples deviate from each other in the angle range close to primary scattering, because of the preferential adsorption of asphaltene. The aggregation of clays by asphaltene also manifests itself in a decrease of specific surface areas determined by N 2-adsorption.