Role of Asphaltene in Stability of Water-in-oil Model Emulsions: The Effects of Oil Composition and Size of the Aggregates and Droplets

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  • Water-in-oil (W/O) emulsions are the most common type of emulsions handled in petroleum
    processes. It is thought that the field emulsions are primarily stabilized by asphaltene-resin
    micelles and several research works have studied the stability mechanisms of asphaltene in crude
    emulsions. However, there is still plenty of research gaps and unanswered question in this area due
    to the complexity of the problem and difficulty of access and crude emulsions processing. These
    challenges can be addressed by investigating the effect of asphaltene on the model emulsions'
    kinetic stability. This study introduces a model W/O emulsion prepared by a new stabilizer
    (Gilsonite) that contains asphaltenes and resins in combination with a non-ionic surfactant (Span
    83). The colloidal characterization of the asphaltene aggregates in the mineral oil and oil blend of
    Toluene and mineral oil was carried out. The size of the asphaltene aggregates in the mineral oil
    was found to increase with the added Gilsonite concentration because of asphaltene precipitation
    and the process of smaller aggregates clumping together, forming flocs. Gilsonite was also found
    to precipitate and stabilize the W/O emulsions with the mineral oil as the external phase where the
    asphaltene precipitation was most severe. The emulsions' least kinetic stability was measured when
    Toluene was added in the oil blend (50% volume fraction), where 100% water phase separation
    was observed with 0.25% Gilsonite concentration. However, the dilute Emulsion (10% water
    content in the emulsion) samples with 25% Toluene revealed higher stability in terms of water
    phase separation than the case with 12.5% Toluene with 20.83% less water separation in a 3-day
    storage period. This observation contradictsthe expected outcome in a thermodynamic perspective
    where the W/O emulsion stability is thought to be merely dependent on the asphaltene
    precipitation. The dilute emulsion with 12.5% Toluene contained asphaltene aggregates larger than
    the emulsion droplets, which cannot contribute to the stability process. The ratio of mean aggregate
    size to the mean droplet size was 133% larger for the dilute emulsion with a smaller fraction of
    Toluene in the oil blend for this case. Therefore, the aggregates' size to droplet size misalignment
    resulted in less stability for this emulsion than the emulsion with higher aromaticity of the oil blend
    despite the very high precipitation rate. This paper presents observations of the effects of the
    asphaltene precipitation rate, size of the aggregates, and size distribution of the emulsion droplets
    on the model W/O emulsions' stability. The significance of the results is in revealing the
    importance of Integrating the thermodynamical and colloidal viewpoints to describe the role of
    asphaltene in stabilizing emulsions. This approach leads to the conclusion that besides the
    asphaltene precipitation, the aggregates' size distribution in relation to the size of the emulsion
    droplets is a critical factor in stabilizing the emulsions. Results presented in this study can be used
    in the design of solvents in enhanced oil recovery, producing model emulsions replicating oil
    reservoir in-situ emulsion features, synthesis of demulsifiers for the emulsions stabilized with
    asphaltene-resin micelles, and other industrial applications. Additionally, Gilsonite was introduced
    as a new additive that can be used to study the role of asphaltene in stabilizing model emulsions.

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    Article (Draft / Submitted)
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    Attribution-NonCommercial 4.0 International