Prediction of the Formation of Water-in-Oil Emulsions - Mathematical Modelling and Numerical Simulation of Oil Pollution Problems - page 57

60 to 80% water, thus expanding the spilled material from 2 to 5 times the original
volume. Most importantly, the viscosity of the oil typically changes from a few hun-
dred to about 100,000mPa s, an increase by a factor of 500-1000. A liquid product
is changed into a heavy, semi-solid material. These thick emulsions are difficult to
recover with ordinary spill recovery equipment.

3.2 Water-in-Oil Types

Fingas and Fieldhouse [ 3 ] found that four clearly-defined water-in-oil types are
formed by crude oil when mixed energetically with water. This was shown by water
resolution over time, by a number of rheological measurements, and by the water-
in-oil products visual appearance, both on the day of formation and 1week later.
Some emulsions were observed for over a year, with the same results. The types are
named stable water-in-oil emulsions, meso-stable water-in-oil emulsions, entrained
water, and unstable water-in-oil types or those-that-did-not form. The differences
among the four types are quite large and are based on at least two water content
measurements and five rheological measurements. More than 400 oils or petroleum
products were studied.
Stable emulsions are reddish-brown semi-solid substances with an average water
content of about 70-80% on the day of formation and about the same 1week later, cf.
[ 2 ]. Stable emulsions remain stable for at least 4weeks under laboratory conditions.
All of the stable emulsions studied, remained so for at least 1year. The viscosity
increase following formation averages 400 times the original viscosity and 1week
later averages 850 times the original viscosity. The average properties of the starting
oil required to form a stable emulsion are: density

− 0.9g/mL; viscosity − 300mPa s;

resin content 0.6.

Meso-stable water-in-oil emulsions are reddish-brown viscous liquids with an
average water content of 60-65% on the first day of formation and less than 30%
1week later. Meso-stable emulsions generally break down within 1week to a sub-
stance called rag with about 20% water content. The viscosity increases over the
initial viscosity on the day of formation averages a factor of 7 and 1week later
averages 5. The average properties of the starting oil required to form a meso-stable
emulsion are: density

− 9%; asphaltene content − 5%; and asphaltene-to-resin ratio −

− 0.9g/mL; viscosity − 1300mPa s; resin content − 16%; and

asphaltene content 0.5. The greatest difference

between the starting oils for stable and meso-stable emulsions are the ratio of vis-
cosity increases (stable 400, first day and 850 in 1week; meso-stable 7, first day and
5 in 1week) and resin content (stable

− 8%; asphaltene-to-resin ratio −

16%).
Entrained water-in-oil types are black viscous liquids with an average water con-
tent of 40-50% on the first day of formation and less than 28% 1week later. The
viscosity increase over the day of formation averages a multiple of two and 1week
later still averages two. The average properties of the starting oil required to form
entrained water are: density

− 9%; meso-stable −

− 0.97 g/mL; viscosity − 60,000mPa s; resin content

− − −

18%; asphaltene content 12%; and asphaltene-to-resin ratio 0.75. The greatest