Составители:
cal experiment has been performed with a freshly prepared sam-
ple.
In studies of water/oil emulsions, two gravitationally sepa-
rated phases were introduced into the rheometer’s cell at the vol-
ume ratio of 1/3, equal to that in the production well (25% v/v of
water). The bitumen concentrates were diluted in the rheometer’s
cell by adding an equal volume of industrial dilutant so that a
studied emulsions contained 25% v/v of bitumen and 20% v/v of
water. Each emulsion was mixed for 1 hour at conditions close to a
maximum rheometer’s torque (shear stresses ≈0.7–0.8 N/m
2
), at a
fixed formation temperature TF in the range from 20 to 60°C. Un-
der constant mixing, each sample was cooled to the lowest operat-
ing (flow) temperature (8–10°C) at the rate of 1–1,5°C per minute.
At each operating temperature, the system was initially main-
tained at a constant shear rate for 20 min. The tests began at the
highest shear rate and measurements continued with unidirec-
tional cylinder rotation in an descending-rate order down to
0.1–0.2 s
-1
.
At each shear rate the torque and shear stress data were col-
lected for 90–120 s and averaged. Before changing to the next op-
erating temperature (in 2°C steps, up to 30°C), the shear rate was
increased to its initial value. With the above procedure, the typical
duration of one experiment was about 6 hours.
3. Results
3.1. Shear stress dependencies of viscosity
For all studied samples the measured flow curves (viscosity
vs. shear stress) exhibited a more or less pronounced shear-
thinning (i.e. non-Newtonian) behaviour. In case of W/O emulsions
and the parent matrix crude oil, the flow curves were approxi-
mately Newtonian at shear stresses ≥0.15–0.4 Pa, depending on
the formation and the flow temperatures. For bitumen emulsions,
the Newtonian approximation could be applied only at much
higher shear stresses, above 0.6 Pa.
As a measure of temperature-induced effects in all samples,
28
Страницы
- « первая
- ‹ предыдущая
- …
- 26
- 27
- 28
- 29
- 30
- …
- следующая ›
- последняя »
