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perature may lead to very large changes of dynamic viscosity,
measured at lower temperatures. All results show a technologically
unfavourable sharp increase of viscosity for the “critical” formation
temperatures of 36–38°C. For example, the viscosity of the water-
free oil, pre-heated to these temperatures, increases by a factor of
70, to 9070 mPa⋅s, as compared to 129 mPa⋅s, measured for un-
heated oil, stored at 19°C. In the water/oil emulsions the corre-
sponding viscosity increase is somewhat lower – from 200 mPa⋅s to
600 mPa⋅s. Obviously, the thermal effects in water/oil emulsions
should be attributed to its oil component. A smaller effect of heat-
ing for water/oil emulsions, as compared to the original crude may
be explained by the fact that the viscosity of the mineralised reser-
voir water, contained in such emulsion, did not show any viscosity
anomalies in the studied temperature range. The results of Figure
1 show that unfavourable increase of viscosity after formation at
“critical” temperatures is also observed in bitumen emulsions. The
reason why this increase is only two-fold (from 60 to 120 mPa⋅s)
may be due to a presence of specially introduced surfac-
tants/stabilisers, as discussed above.
The data of Figure 1 reveal the
small width of the “critical range” of
formation temperatures, leading to the
observed unfavorable thermal effects.
At the FWHM of the crude oil viscosity
peak, this TF range may be
determined as 2,2°C. The most conser-
vative estimates at the base of the
viscosity peak give for the critical TF
range the value not exceeding 10°C.
In course of all experiments, the
results of the thermal treatment
(modified viscosities) were still
detected even after prolonged (up to 6 hours) annealing at increas-
ing flow temperatures in conditions of a continuing mechanical
agitation.
19
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