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Exploration, Recovery, and Transportation
the reservoir conditions (Figure 6.8). In addition, oil viscosity is also a function of temperature
and  API  gravity (Speight, 2000, and references cited therein). Thus for heavy crude oil samples
with API gravity ranging from 4 to 21°API (1.04–0.928 kg/m 3 ),
log log
A B log T 46
(
)
†(
)
ms a
+ = -
+ 0
where
μσ is oil viscosity in cP
T is temperature in °F
A and B are constants
α is an empirical factor used to achieve a straight-line correlation at low viscosity
This equation is usually used to correlate kinematic viscosity in centistokes, in which case an α of
0.6–0.8 is suggested (dynamic viscosity in cP equals kinematic viscosity in cSt times density in g/mL).
An alternative equation for correlating viscosity data is
m = ae
b T
/ *
where
a and b are constants
T* is the absolute temperature
Thermally enhanced oil recovery processes add heat to the reservoir to reduce oil viscosity
and/or to vaporize the oil. In both instances, the oil is made more mobile so that it can be more
Athabasca
Cold Lake
Viscosity, cP
10
6
10
5
10
4
10
3
10
2
10
1
100
200
300 °F
50
100
Light crude oil
Heavy oil
(Lloydminster)
150 °C
Temperature
FIGURE 6.8 Variation of petroleum, heavy oil, and tar sand bitumen viscosity with temperature.