PROPERTIES OF RESERVOIR GASES - Petroleum Reservoir Fluid Property Correlations - page 9

Table 2-1. Description of the data set used to evaluate z-factor correlations based on gas specific
gravity (6,000 lines of data from 1,434 PVT reports of worldwide origins)
Variable

Minimum Median Mean Maximum

Pressure, psia 14.7 2,750.0 3,415.2 18,050.0

Temperature, ºF 35.0 220.0 217.2 418.0

Gas specific gravity 0.5590 0.8301 0.9002 2.2380

Hydrogen sulfide, mole fraction 0.0000 0.0000 0.0105 0.5137

Carbon dioxide, mole fraction 0.0000 0.0085 0.0260 0.7198

Nitrogen, mole fraction 0.0000 0.0020 0.0110 0.4954

Gas z-factor 0.4000 0.9340 0.9959 2.3500

Piper et al. used approximately one-quarter of these data to develop
their correlations. Apparently none of the other researchers had access
to any of these data.
Gas z-factors calculated with several correlations were compared
with the laboratory-measured z-factors. The results are given in table
2-2. The evaluation criteria, average relative error and average absolute
relative error, are defined in chapter 1. A positive value of ARE indicates
that the calculated value is larger than the measured value.

Table 2-2. Average relative errors of several gas z-factor correlations based on gas specific gravity
compared with the data set of table 2-1
Pseudocritical Properties Correlation

z-factor Correlation Average Relative

Error, %

Average Absolute
Relative Error, %

Piper et al. (1999) Hall-Yarborough (1973) 0.307 1.562

Piper et al. (1999) Dranchuk-Abou-Kassem (1975) 0.296 1.590

Piper et al. (1999) Brill-Beggs (1974), (1977) † -0.253 1.731

Sutton (2007)* Hall-Yarborough (1973) -0.548 1.621

Sutton (2007)* Dranchuk-Abou-Kassem (1975) -0.422 1.511

Elsharkawy-Elkamel (2000) Dranchuk-Abou-Kassem (1975) 0.010 1.821

Elsharkawy-Elkamel (2000) Hall-Yarborough (1973) -0.014 1.812

Standing (1977)* Hall-Yarborough (1973) -1.084 1.968

Standing (1977)* Dranchuk-Abou-Kassem (1975) -1.010 1.949

Standing (1977)* Brill-Beggs (1974), (1977) † -1.609 2.320

Elsharkawy et al. (2000) Hall-Yarborough (1973) 1.200 2.434

Elsharkawy et al. (2000) Dranchuk-Abou-Kassem (1975) 1.185 2.452

Sutton (1985)* Dranchuk-Abou-Kassem (1975) 1.746 2.878

Sutton (1985)* Hall-Yarborough (1973) 1.769 2.887

Londono et al. (2005) Dranchuk-Abou-Kassem (1975) -1.044 3.254

Piper et al. (1999) Nishuimi-Saito (2005) ‡ 5.646 5.911

Londono et al. (2005) Nishuimi-Saito (2005) ‡ 5.157 6.432

Piper et al. (1999) Papay (1968) 15.113 16.166

† From Standing (1977) ‡ Nishuimi-Saito equation with

* Included Wichert-Aziz correlation for hydrogen sulfide and carbon dioxide

coefficients derived by Londono et al.