PROPERTIES OF BLACK OILS - Petroleum Reservoir Fluid Property Correlations - page 80

(3.18g)

bs

Then the reservoir oil density at bubblepoint pressure may be
calculated with equation (3.18h).

(3.18h)

Note that the value of the gas specific gravity in equation (3.18b)
should be the weighted-average specific gravity of the total surface gas.
Thus, either equation (3.4) or equation (3.6) is usually necessary with
equations (3.5) and (3.2) used to obtain the stock-tank gas properties.
Equation (3.18c) requires the specific gravity of the separator gas.

Evaluation of proposed correlation equations for reservoir oil
densities at reservoir pressures less than bubblepoint pressure
Statistics of the data set used to evaluate reservoir oil density
correlations for reservoir pressures equal to and less than bubblepoint
pressures are given in table 3-16.

Table 3-16. Statistics of data set used to evaluate reservoir oil density correlations at pressures
equal to and less than bubblepoint pressures (6,475 lines of data from 745 reservoir fluid studies
with worldwide origins)
Laboratory measurement

Minimum Median Mean Maximum

Bubblepoint pressure, p b , psia 139.7 2,114.7 2,213.3 7,750.0

Reservoir temperature, T R , ºF 70.0 182.0 185.4 320.0

Solution gas-oil ratio at p b , R sb , scf/STB 13.2 520.0 580.2 1,808.0

Stock-tank oil gravity, API , ºAPI 11.6 38.3 37.0 56.2

0.5548 0.7840 0.7963 1.4720

Separator gas specific gravity, γ gSP

Reservoir oil density, ρ oR , lb/cu ft 32.57 45.57 45.67 59.89

McCain and Hill showed that the reservoir oil density equations
given above, equations (3.18a)-(3.18h), which originally were developed
for use at bubblepoint pressures, can be used at pressures below the
bubblepoint pressure. 33 Simply substitute a selected value of pressure,
p , for the bubblepoint pressure, p b , in equation (3.18e) and substitute
the solution gas-oil ratio at that pressure, R s , for the solution gas-oil