Geoscience Reference
In-Depth Information
Table 2-3. Average relative errors of several gas z-factor correlations based on gas specific
gravity compared with gases with nonhydrocarbon components from the data set of table 2-1.
All calculations used Dranchuk-Abou-Kassem z-factor equations.
Correlation
H
2
S > 5 mol%*
CO
2
> 5 mol%
†
N
2
> 5 mol%
‡
H
2
S + CO
2
+ N
2
> 10 mol%
§
Average
relative
error
Average
absolute
relative
error
Average
relative
error
Average
absolute
relative
error
Average
relative
error
Average
absolute
relative
error
Average
relative
error
Average
absolute
relative
error
Sutton (2007)
-0.7
1.9
0.1
1.7
-0.8
2.1
-0.2
1.9
Piper et al. (1999)
1.9
2.9
0.6
1.8
0.3
2.7
0.6
2.2
Standing (1977)
-0.5
2.0
-0.3
2.2
-1.5
2.6
-0.4
2.2
Elsharkawy-Elkamel (2000)
1.3
2.8
-1.0
2.8
-3.9
4.7
-2.1
4.0
Londono et al. (2005)
9.7
13.5
-1.2
6.0
-2.5
6.5
-0.1
8.4
Elsharkawy et al. (2000)
16.6
17.4
2.9
4.4
-0.1
4.7
4.8
7.9
Sutton
(1985)
30.4
30.6
6.6
6.8
1.7
4.5
11.5
12.6
†
715 lines of data
‡
336 lines of data
§
681 lines of data
* 177 lines of data
Figures 2-2 through 2-4 show the relative errors for Piper et al.,
Sutton (2007), Standing, and Elsharkawy-Elkamel correlations for 11
approximately equal-sized subsets of the data sorted and then sliced on
gas specific gravity, reservoir pressure, and reservoir temperature.
The Piper et al. correlation equations give the best results across
the full range of the data. The Sutton (2007) equations are essentially
equivalent. The deviations of the Standing equations at higher values
of gas specific gravity are not surprising; he had limited data for high
specific gravity gases.
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