Prediction of the Formation of Water-in-Oil Emulsions - Mathematical Modelling and Numerical Simulation of Oil Pollution Problems - page 58

differences between the starting oils for entrained water-in-oil compared to stable
and meso-stable emulsions are the viscosity of the starting oil (entrained starting oil
averages 60,000mPa s compared to 200mPa s for stable emulsions and 1300mPa s
for meso-stable emulsions) and the ratio of viscosity increase (entrained 2, first

day and 2 in 1week; stable 400, first day and 850 in 1week; meso-stable 7, first day
and 5 in 1week). Entrained water-in-oil types appear to be applicable to viscous oils
and petroleum products, but not extremely viscous products.
Unstable water-in-oil emulsion types or those oils that do not form any of the
other three types are characterized by the fact that the oil does not hold significant
amounts of water following mixing with water [ 2 ]. There is a much broader range of
properties in the starting oil than for the other three water-in-oil states. For example,
viscosities are very low or very high. Included in this group are light fuels such as
diesel fuel and very heavy, viscous oil products such as heavy residual oils.
The differences between some of the basic properties of emulsions and water-in-
oil types are shown in Fig. 3.1 . Figure 3.1 uses umbrella or spider graphs to show
the relationship of the ten average properties of each water-in-oil type compared to
another water-in-oil type. Moving around the graph, the relative water content on the
first day is plotted, then the water content after 1week, then the starting oil density,
then the starting oil viscosity, then the saturate, aromatic, resins and asphaltene
contents. After this, the graph shows the asphaltene/resin (A/R) content, then the
wax content. Each of these parameters are scaled on this graph from 1 to 10 based on
the distribution from the lowest to highest relative value. As can be seen from these
figures, there are significant differences between the various water-in-oil types.
The viscosity and water content differences among the four types of water content
in oil are shown in Fig. 3.2 . Figure 3.2 a shows the water content change over 1year.
Stable emulsions, on average, begin at a high level (about 78%) and lose little water
over 1year. Meso-stable emulsions, on the other hand, begin at about 65% and lose
most of this water within a few days. Entrained water-in-oil types pick up only about
40% water and only slowly lose this over 1year. Unstable water-in-oil types pick up
only a few percent of water and this does not change much over 1year. Figure 3.2 b
shows the apparent viscosity over 1year. This graph shows that the apparent viscosity
of stable emulsion increases over the period of 1year and the others generally decline
or only increase a small amount. Thus, after a few months, the stable emulsion will
have the greatest viscosity.

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3.3 Stability Indices

Fingas and Fieldhouse [ 3 ] carried out tests of several indices of stability, a single
value that could provide good discrimination between water-in-oil types even on the
first day. This was felt to be necessary as the water content alone was not entirely
discriminating because some of the water loss occurs within hours or days, especially
for meso-stable emulsions. A new stability index was found, and serves to describe
the emulsion stability quite well.