Rheological and morphological
properties of heavy crude oil-in-water
(O/W) emulsions have been studied. Two series of emulsions were considered:
first, the surfactant type remained constant, while the continuous
phase content was varied and second, the surfactant type was varied
while the continuous phase content remained constant. Under stress-controlled
shearing, all samples exhibit viscoplastic behavior. The rheological
properties are directly related to the morphology of the emulsions
which vary in size of dispersed phase droplets and their inherent
structure. Adding a surfactant characterized by a high value of interfacial
oil–water tension results in a decrease in the yield stress
(which is a measure of the interparticulate structure strength). The
same effect is attained by increasing the water content. Meanwhile,
these two factors determine the viscosity which can be much lower
than that of the basic heavy crude oil if the O/W type of emulsions
has been created. Special attention was paid to the viscoelastic properties
which have been scarcely reported. Correlations were found between
the surfactant properties, composition of the emulsion, and rheological
characteristics of emulsions (yield stress, apparent viscosity, and
viscoelastic properties), which allows for reduction in the crude
oil viscosity down to a low enough level acceptable for pipe transportation.