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sions the effects of the thermal preload are largest at low flow
temperatures and are gradually levelled off as the flow tempera-
ture is increased up to 30°C. Qualitatively similar (but much
stronger) effects were observed also for the matrix crude oil
(cf. Figs.2,3).
For the bitumen emulsions (Fig.1 B) a moderate thermal pre-
load (TF=36°C) also leads to the viscosity increase, but only at flow
temperatures above 13–14°C. At flow temperature of 16°C the vis-
cosity increases from 61 mPa⋅s (RT fabrication) to 115 mPa⋅s.
However, below 13°C there is an apparent reversal of the TF effect:
viscosity values for TF=36°C show a tendency to be lower than
those for TF=24°C. A higher thermal preload (TF=45°C), leads to a
general decrease of measured viscosities but, as distinct from crude
oil emulsions, these viscosities (at least for flow temperatures
above 13°C) remain larger than those measured after RT forma-
tion.
3.3. The critical formation temperatures and
the effect of thermal memory
As follows from the previous section, relatively small varia-
tions of the thermal preload (formation temperature) may lead to
quantitatively large and even qualitatively different changes in the
rheological parameters, measured
at lower temperatures in various
types of petroleum emulsions. In
order to determine the role of oil
emulsion constituents in this ef-
fect, we made similar rheological
measurements with the separated
phases. The viscosity of the miner-
alised reservoir water did not show
any peculiarities in the studied
ranges of the formation/flow tem-
peratures. The viscosity of the ma-
trix crude oil showed qualitatively
30
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