Page 72 - Introduction to Petroleum Engineering

56 PROPERTIES OF RESERVOIR FLUIDS
solution (R in SCF/STB), gas gravity (γ ), temperature (T) in°F, and API gravity
g
s
(°API) with the following correlation:
.
.
p = 18 2 ( A −1 4 ) (3.15)
b
with
.
 R  083
.
A =   s   10 0 00091 T −0 0125 ×° API (3.16)
.
 γ g 
Example 3.2 Bubble‐point Pressure
Calculate bubble‐point pressure for reservoir temperature of 220°F, oil gravity
of 35°API, and gas gravity of 0.68. The amount of gas dissolved in the oil is
350 SCF/STB.
Answer
Use Equations 3.15 and 3.16 with the values provided:
.
 350 SCF/STB  083
A =   10 0 00091 (220 ° F)−0 0125 (35 ° API) = =103 11
.
.
.
 068 
.
P = 18 2 (103 11. −14 ) = 1851 psi
.
.
b
The plot in Figure 3.4 was created using the correlation of Equations 3.15 and 3.16
with the properties of Example 3.2 with R varying from near 0 up to 350 SCF/STB.
s
Above the BP pressure of 1851 psi, R is constant at 350 SCF/STB.
s
400
350
Dissolved gas (SCF/STB) 250
300

200
150
100
50
0
0 500 1000 1500 2000 2500 3000
Pressure (psi)
FIGURE 3.4 Demonstration of the correlation in Equations 3.15 and 3.16 with
properties from Example 3.2.