EFFECTS OF ASPHALTENE AGGREGATION IN MODEL HEPTANE-TOLUENE MIXTURES ON STABILITY OF WATER-IN-OIL EMULSIONS

As part of an ongoing investigation into the stability of water-in-cru de oil emulsions, model oils have been utilized to further probe the e ffects of crude solvency as well as specific resin-asphaltene interact ions on emulsion stability. These model oils were constructed by disso lving varying amounts of resins and/or asphaltenes in a mixture of hep tane and toluene. The resins and asphaltenes used in this study were i solated from four different crude types-Arab Berri (AB), Arab Heavy (A H), Alaska North Slope (ANS), and San Joaquin Valley (SJV)-and charact erized in a previous study using heptane precipitation of the asphalte nes followed by an extrographic separation of the resins from silica g el. Asphaltenes dissolved in heptol at concentrations of just 0.5% wer e shown to generate emulsions which were even more stable than those g enerated from their respective whole crude oils. Some types of resins (e.g., from AH and SJV) also demonstrated an ability to stabilize emul sions although these resin-stabilized emulsions were considerably less stable than those prepared with asphaltenes. The primary factors gove rning the stability of these model emulsions were the aromaticity of t he crude medium (as controlled by the heptane:toluene ratio), the conc entration of asphaltenes, and the availability of solvating resins in the oil (i.e., the resin/asphaltene or R/A ratio). The model emulsions were the most stable when the crude medium was 30-40% toluene and in many cases at small R/A ratios (i.e., R/A less than or equal to 1). Th is strongly supports the theory that asphaltenes are the most effectiv e in stabilizing emulsions when they are near the point of incipient p recipitation. The types of resins and asphaltenes used to construct th ese model oils also played a role in determining the resultant emulsio n stability which indicates the importance of specific resin-asphalten e interactions. The interfacially active components that stabilized th ese model systems were the most polar and/or condensed portions of the resin and asphaltene fractions as determined by elemental and neutron activation analyses. All of these results point to the significance o f the solubility state of the asphaltenes in determining the emulsifyi ng potential Of these crude oils. (C) 1997 Academic Press.