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the same effects of formation temperature, but much more pro-
nounced than those in the studied emulsions, as illustrated in
Fig.2.
Filled triangles in Fig.2 denote the viscosity values (measured
at 16°C) for the bitumen emulsions prepared at different formation
temperatures. Filled circles denote the analogous data for the
crude oil emulsions (measured at 12°C). The results for the matrix
crude oil (also measured at 12°C) are denoted by open circles and
show a very sharp peak of viscosity for the “critical” formation
temperature of 38°C.
The peak viscosity value is 9070 mPa⋅s, as compared to 129
mPa⋅s, measured after room temperature (19°C) formation of the
crude oil sample. The data of Fig.2 reveal the small width of the
“critical range” of formation temperatures, leading to the observed
thermal effects. As the FWHM of the crude oil viscosity peak, this
TF range may be determined as 2,2°C. The most conservative es-
timates at the base of the viscosity peak give for the critical TF
range the value not exceeding 10°C.
The results of Fig.2 definitely prove that the observed effects
of a thermal preload in the W/O emulsions are related mainly to
the changes in the properties of the matrix crude oil. The consid-
erably smaller effect in the bitumen emulsions may be due to a
presence of specially introduced surfactants/stabilisers, as dis-
cussed in section 4.3.
In course of all experiments, the results of the thermal pre-
loads (modified viscosities) were still detected even after prolonged
(up to 6 hours) annealing at increasing flow temperatures in condi-
tions of a continuing mechanical agitation. This indicates that
some long-lived residual structures remained in the emulsions af-
ter the fabrication processes at “critical” temperatures (the effect of
long-term “thermal memory”). In the matrix crude oil, this “ther-
mal memory” was found to extend for a period of at least four
months, as revealed by viscosity measurements after storage at
room temperatures.
31
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