Prediction of the Formation of Water-in-Oil Emulsions - Mathematical Modelling and Numerical Simulation of Oil Pollution Problems - page 63

have been used to study formation mechanisms and stability of emulsions [ 4 ].
Standard chemical techniques, including Nuclear Magnetic Resonance (NMR),
chemical analysis techniques, Near-infrared spectroscopy (NIR), microscopy,
interfacial pressure, and interfacial tension, are also being applied to emulsions.
These techniques have largely confirmed findings noted in the dielectric and rheo-
logical mechanisms.
Most researchers studied the stability of emulsions by measuring the amount of
water resolved with time [ 4 ]. This certainly is the baseline method. Some researchers
also subjected the emulsions to centrifugation to assess stability.

3.4.4 The Overall Theory of Emulsion Formation

The data suggest that the water-in-oil types are stabilized by both asphaltenes and
resins, but for greater stability, resin content should exceed the asphaltene content
slightly [ 3 ]. However, excess resin content (A/R about 0.6) apparently destabilizes

the emulsion. This does not consider the question of different types of asphaltenes
or resins. A high asphaltene content (typically

>

10%) increases the viscosity of the
oil such that a stable emulsion will not form. Viscous oils will only uptake water as
entrained water and will slowly lose much of this water over a period of about 1week.
Viscous oils (typically

>

1000mPa s) will not form stable or meso-stable emulsions.
Oils of low viscosity or without significant amounts of asphaltenes and resins will
not form any water-in-oil type and will retain less than about 6% water. Oils of very
high viscosity (typically

>

>

20,000mPa s) will also not form any of these water-in-oil
types and thus are classified as unstable. This is probably due to the inability of water
droplets to penetrate the oil mass.
The start of the process is the injection of water droplets into the oil mass. This
would typically occur as the result of turbulence or wave action. This also could
occur as the result of oil injection into water, such as from an underwater blowout.
Once in the oil mass, the water droplets may coalesce and sink to the bottom unless
these water droplets are somehow stabilized. Asphaltenes probably reside in the oil
in the form of resin-solvated agglomerates. They are not likely to stabilize the water
droplets immediately as the large asphaltene-resin agglomerates migrate too slowly.
If, however, the oil has a viscosity between about 50-5000mPa s, the water droplets
will move slowly, allowing time for some chemical stabilization. It is thought that
resins, weakly stabilize the water droplets initially. Resins are also polar compounds
and can become associated with polar water. Once stabilized by resins, the large
asphaltenes will move toward the water droplets and will form elastic films around
the water droplets. The ratio of asphaltene to resins can affect this process. If the
quantity of resins is too high, they will solvate the asphaltenes to the extent that their
migration is affected and will also create a barrier between the asphaltenes and the
water droplets. Thus in the case of too high resin content, destabilization will also
occur. It is thought that this destabilization is the origin of meso-stable emulsions.
If the viscosity of the oil is too high, water droplets cannot penetrate the oil mass
to a great extent and thus emulsions are not formed. At moderate oil viscosities, about