Viscosity Prediction from the Crude Assay
Unlike sulfur content and gravity, viscosity cannot be arithmetically related directly
to components. To determine the viscosity of a blend of two or more components, a
blending index must be used. A graph of these indices is given in Maxwell’s Data
Book on Hydrocarbons, and part of this graph is reproduced in Fig. 11. Using the
blending indices and having divided the TBP curve into components as before, the
viscosity of the fraction can be predicted as shown in Table 6.
800
700
600
500
400
300
200
100
0
0
10
20
30
40
50
60
Sulfur
% Vol Distilled or Mid vol
70
80
90 100
0 0
10
20
30
40
50
API
Temperature
Temperature °C
API
60
70
80
1.0
2.0
3.0
% Wt Sulfur
Fig. 9 Typical crude assay curves (based on Kuwait crude)
Introduction to Crude Oil and Petroleum Processing
25