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coefficient of isothermal compressibility, c ofb , will be used for calculating
values of this property at pressures greater than bubblepoint pressure.
However, care must be taken in the selection of these equations such
that the relationship is continuous, i.e., the values of oil density coincide
at the bubblepoint pressure.
Evaluation of proposed correlation equations for reservoir oil
densities at reservoir pressures equal to bubblepoint pressure
Statistics of the data set used to evaluate reservoir oil density
correlation equations for reservoir pressures equal to bubblepoint
pressures are shown in table 3-14.
Table 3-14. Statistics of data set used to evaluate oil density correlation equations at bubblepoint
pressures (756 lines of data from 756 reservoir fluid studies with worldwide origins)
Laboratory measurement
Minimum
Median
Mean
Maximum
Bubblepoint pressure, p b , psia
96.7
2,154.7
2,197.7
6,714.7
Reservoir temperature, T R , ºF
74.0
180.0
181.9
327.0
Solution gas-oil ratio at p b , R sb , scf/STB
10.0
597.0
643.9
1,975.0
Stock-tank oil gravity, API, ºAPI
11.4
39.2
37.8
55.0
Separator gas specific gravity, γ gSP
0.5560
0.8240
0.8276
1.2370
Reservoir oil density, ρ oR , lb/cu ft
31.12
42.97
43.75
58.20
An evaluation using the data set described in table 3-14 of published
correlation equations for estimating reservoir oil densities for reservoir
pressures equal to bubblepoint pressures may be found in table 3-15.
Table 3-15. Evaluation of published reservoir oil density correlation equations at bubblepoint
pressures reveals the most reliable correlations.
Predicted reservoir oil densities
ARE, %
Correlation
AARE, %
Standing (1977)/Witte (1987)/McCain-Hill (1995)
0.39
0.88
Standing (1977)/Witte (1987)
0.61
1.03
Standing (1977)*
1.14
1.39
Labedi (1990)
-0.24
1.53
Ahmed equation (4.32) (1989)
-1.17
1.66
Ahmed equation (4.35) (1989)
0.34
2.10
Sutton (2008)
0.13
2.12
Hanafy et al. (SPE 37439, 1997)
-0.06
4.24
Author combined Standing B ob equation (Standing, 1977) with McCain
* Author restricted the correlation to a specific geographical area.
Author used Standing ∆ρ p and ∆ρ T equations (Standing, 1977).
ρ oR equation (McCain, 1973).
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