Abstract
Asphaltene molecules play a pivotal role in reservoir fluid characterization. As a result of the high complexity of these molecules, there is still an active debate in the scientific community about their physicochemical properties and the structural elucidation, despite a myriad of published studies. It is commonly agreed that asphaltenes, a fraction of reservoir crude oils, exhibit strong interfacial activity and cause many production challenges. In this work, the structure and interfacial activity of 11 characterized asphaltene samples, extracted from 11 different reservoir crude oils from the Middle Eastern region, were analyzed using Raman spectroscopy and pendent drop tensiometry. Additionally, contact angle measurements and atomic force microscopy (AFM) were executed on selected samples. The Raman analysis revealed that the 11 asphaltene batches have similar structural characteristics with the annulated core ranging from 1.43 to 1.66 nm in diameter, which corresponds to 6-7 fused aromatic rings. Interfacial tension (IFT) was measured using the pendent drop technique, by creating a drop of deionized water in a bulk of the respective asphaltene solution in toluene. IFT 90 min values were in the range between 28.3 and 32.6 mN m(-1) For one of the asphaltenes, aggregation in the toluene solution was visible by the naked eye. Interestingly, this asphaltene sample showed the weakest influence in terms of IFT reduction, indicating that aggregation reduces the interfacial activity. On the basis of the IFT results, three of the asphaltene samples, exercising different interfacial activity, were investigated for their adsorption tendency toward a carbonate surface using AFM. Topographic images show asphaltene adsorption. The contact angle for water on asphaltene-conditioned surfaces was higher than that for unconditioned surfaces, indicating that the calcite surface was rendered more oil-wet. Increasing the concentration of the asphaltenes in the conditioning solution did not alter the surface to more oil-wet.C