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The stability of water-in-crude oil emulsions is frequently attributed to a rigid asphaltene film at the water/oil interface. The rheological properties of these films and their relationship to emulsion stability are ill defined. In this study, the interfacial tension, elastic modulus, and viscous modulus were measured using a drop shape analyzer for model oils consisting of asphaltenes dissolved in toluene for concentrations varying from 0.002 to 20 kg/m(3). The effects of oscillation frequency, asphaltene concentration, and interface aging time were examined. The films exhibited viscoelastic behavior. The total modulus increased as the interface aged at all asphaltene concentrations. An attempt was made to model the rheology for the full range of asphaltene concentration. The instantaneous elasticity was modeled with a surface equation of state (SEOS), and the elastic and viscous moduli, with the Lucassen-van den Tempel (LVDT) model. It was found that only the early-time data could be modeled using the SEOS-LVDT approach; that is, the instantaneous, elastic, and viscous moduli of interfaces aged for at most 10 minutes. At longer interface aging times, the SEOS-LVDT approach was invalid, likely because of irreversible adsorption of asphaltenes on the interface and the formation of a network structure.

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Surface Coverage in Stabilizing Water-In-Bitumen Emulsions (Unpublished master's thesis).

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Oilfield emulsions are often stabilized by asphaltenes but inorganic solids can impact both emulsion stability and rag layer accumulation. In this study, the effect of inorganic solids on emulsion stability and emulsion layer growth was investigated using batch and continuous separations performed on water‐in‐oil emulsions stabilized by asphaltenes. The emulsions were prepared at 60 °C from an organic phase consisting of solids, asphaltenes, n‐heptane, and toluene and an initial water phase volume of 0.50. Three types of coarse solids were considered: 12 μm kaolin, 18–32 μm silica, and 32–63 μm silica with wettabilities ranging from 50 to 125°. In batch experiments, the coalescence rate was determined from the change in height of the free water and oil layers over time as the emulsion coalesced. In continuous experiments, emulsion layer growth was measured as the emulsion was continuously fed into a vertical separator. The data were modelled with a material balance that included a coalescence rate equation. In the absence of solids, the continuous emulsion layer growth rate and ultimate stability correlated well to batch coalescence parameters. The addition of the coarse solids at concentrations below 5 g/L accelerated coalescence rates. Above 5 g/L, the solids increased emulsion stability indicating that they form a steric barrier between the droplets. Even if the feed is below this threshold, the solids accumulate in the rag layer until the threshold is reached, the emulsion becomes stable, and the performance of the continuous separation can no longer be predicted from batch tests.