PROPERTIES OF BLACK OILS - Petroleum Reservoir Fluid Property Correlations - page 81

ratio at the bubblepoint, R sb , in equations (3.18b) and (3.18d). Values of
solution gas-oil ratio at pressures less than bubblepoint pressure may be
estimated with equations (3.8a)-(3.8f).
Figure 3-20 shows that the results are valid even at very low pressures.
An evaluation of published correlations for estimating reservoir
oil densities for reservoir pressures equal to and below bubblepoint
pressures is in table 3-17. Labedi suggested that his procedure is valid at
pressures below bubblepoint pressures. Unfortunately, an evaluation was
not possible because the data set did not have values of the pressures of
the first-stage separators that are required in his equations. 34 Apparently
Sutton did not intend for his correlation to be used at pressures less
than bubblepoint pressure. 35

Table 3-17. Evaluation of published reservoir oil density correlation equations at reservoir
pressures equal to and less than bubblepoint pressures reveals the most reliable correlations.

Predicted reservoir oil densities
ARE, % Correlation AARE, %

Standing (1977)/Witte (1987)/McCain-Hill (1995) -0.01 1.40

Standing (1977)/Witte (1987) -0.59 1.58

Standing (1977)* 0.24 1.67

Ahmed equation 4-32 (1989) † -0.53 1.63

Ahmed equation 4-35 (1989) ‡ -0.76 2.27

Hanafy et al. (SPE 37439, 1997)* -1.04 6.33

† 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).

McCain and Hill used approximately 30% of the data described
in table 3-16 to evaluate the possibility of using these equations at
pressures less than the bubblepoint pressure. Standing, Witte, Labedi,
Ahmed, and Hanafy did not use any of these data.
The data described in table 3-16 were sorted and sliced into eight
subsets of approximately 800 lines of data based on reservoir oil density,
stock-tank oil gravity, solution gas-oil ratio, and reservoir temperature.
Values of ARE and AARE for these subsets of the data are given in figures
3-20 through 3-24.