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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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- Author(s) / Creator(s)
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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
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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. -
- Date created
- 2021-03-16
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- Subjects / Keywords
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- Type of Item
- Article (Draft / Submitted)