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Vazquez and Beggs, and Kartoatmodjo and Schmidt used essentially
all of the data described in table 3-26 in preparation of their correlation
equations. 48 It is not known if the other researchers had access to
these data.
The data set described in table 3-26 was sorted and sliced into 10
subsets of approximately equal size, approximately 200 lines of data
each. The results of calculating ARE and AARE on these subsets for
several of the better correlation equations are shown in figures 3-39
through 3-44. Several of the correlation equations depend on values of
oil viscosities at bubblepoint pressures. Equations (3.23a)-(3.23e) were
selected to determine these values since they represent the best available
procedures for use at bubblepoint pressures.
Recommended correlation equations for estimation of reservoir oil
viscosities at reservoir pressures greater than bubblepoint pressure
Although there does not appear to be a favorite when examining the
ARE figures, the Petrosky-Farshad equations appear to have an edge in
the AARE figures.49 49 Thus, the recommended correlation equations are
given in equations (3.24a) and (3.24b).
(3.24a)
where
(3.24b)
Values of oil viscosities at bubblepoint pressures for use in equations
(3.24a) and (3.24b) are calculated with equations (3.23a)-(3.23e) using
values of solution gas-oil ratios at bubblepoint pressures. This ensures
the continuity of the values of reservoir oil viscosities as reservoir
pressure declines through the bubblepoint pressure.
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