Influence of asphaltenes and resins on water/model oil interfacial tension and emulsion behavior: Comparison of extracted fractions from crude oils with different asphaltene stability.

Asphaltenes and resins make a major contribution for the formation of stable water-in-oil emulsions during crude production, which could affect process operations and increase costs. The purpose of this investigation is to study the influence of these molecular substances from two different crude oil samples (regarding asphaltene stability) on the water-model oil interfacial tension, along with their effect on the emulsion stability. Asphaltene stability of these crude oils presented a marked difference when studied in our past work, with asphaltene precipitation onset that vary from 56 to 75 n- heptane wt %, despite their similar SARA composition. This difference on asphaltene stability was contrasted in this work with the chemical characterization, interfacial activity, and emulsion behavior of crude oil asphaltenes, resins, and their mixtures using toluene solutions. For each crude oil, resins and asphaltenes were extracted and characterized by XRD, SEM/EDS, FTIR, and elemental analysis, to better understand their molecular structure and surface-active species content. Then, it was prepared different model oil solutions in toluene, varying the content of asphaltenes and resins (500, 1,000, and 2000 mg/L). Additionally, it was prepared 2000 mg/L asphaltene/resin mixtures with different ratios (75:25 wt%, 50:50 wt%, and 25:75 wt%). Dynamic interfacial tension between the model oil and water was measured by intermediate of a Du Noüy ring method. Afterward, each model system was emulsified by adding water (at the same volumetric ratio) in a bottle test and stability was analyzed. For the sample with lower stable asphaltenes, a rapid stabilization of the dynamic interfacial tension (IFT) was observed, together with a decrease of IFT from 26.8 to 24.2 mN/m at the limit of asphaltene content studied. On the contrary, for the high stable asphaltenes sample, a transient dynamic IFT behavior was observed, until reach 12.0 mN/m (the lower operational equipment limit). Similar results were obtained for resins model solutions for both crude oils tested. For asphaltene obtained from the sample with lower asphaltene stability, the emulsions presented high stability (for a 24 h test). Besides for the high asphaltene stability sample and resins model oils, all emulsions prepared were unstable. Useful insights are given by the oil fractions chemical characterization, suggesting that smaller sized molecules from high stable crude oils have a predominant effect on IFT reduction, while larger molecules from less stable oils are responsible for the emulsion stability. • Interfacial activity of asphaltenes or resins extracted from crude oils with different stability was compared in model-oil/water systems. • Asphaltenes from lower stable crude oil present a faster stabilization of the dynamic interfacial tension (IFT). • Contrary, asphaltenes from high stable crude oil presented a wider transient dynamic IFT behavior with maximum decrease of IFT. • Resins presented longer stabilization times and lower IFT values. • Results suggest that smaller sized molecules have a predominant effect on IFT, while larger molecules are responsible for the emulsion stability. [ABSTRACT FROM AUTHOR]