PROPERTIES OF BLACK OILS - Petroleum Reservoir Fluid Property Correlations - page 40

Most of the data described in table 3-1 were used to prepare
correlation equations (3.5) and (3.6). 6
The data were separated into groups based on separator pressures,
separator temperatures, and separator producing gas-oil ratios. Table
3-5 shows that equations (3.1), (3.2), and (3.5) give good results across
the ranges of separator conditions and producing gas-oil ratios of the
full set of data.

Table 3-5. The weighted-average surface-gas specific gravities estimated with equations (3.5),
(3.2), and (3.4) are consistent across the data set.

Predicted weighted-average surface-gas specific gravities
ARE, %

Data set Number of lines of data AARE, %

All data 618 -0.7 2.2

p SP ≤ 50 psig 274 -0.6 1.9

50 psig < p SP ≤ 100 psig 245 -1.2 2.4

p SP > 100 psig 99 0.4 2.4

T SP ≤ 80ºF 389 -0.2 2.0

T SP > 80ºF 229 -1.4 2.5

R SP ≤ 300 scf/STB 170 -1.5 3.7

300 scf/STB < R SP ≤ 700 scf/STB 205 -0.5 2.1

R SP > 700 scf/STB 243 -0.3 1.3

Bubblepoint Pressures at Reservoir Temperatures

A value of bubblepoint pressure at reservoir temperature is required
for nearly all of the oil property correlation equations. Sometimes a
value of bubblepoint pressure can be deduced for an oil if pressure-
production data are available for that particular reservoir. 7 However,
the usual situation is that a value of bubblepoint pressure must be
estimated with correlation equations.

Evaluation of proposed correlation equations for bubblepoint
pressures at reservoir temperatures
Table 3-6 gives statistics of the data set used to evaluate published
correlation equations for bubblepoint pressures at reservoir
temperatures. The data include the full range of values of the
independent variables normally associated with black oil reservoirs.
Comparisons of the measured bubblepoint pressures from the data
described in table 3-6 with the results of calculations with 24 sets of
correlation equations from the literature are shown in table 3-7.