Page 129 - Fundamentals of Reservoir Engineering

PVT ANALYSIS FOR OIL 68

5.615 F 5.615 F c b
R R − = R − d
s = si f c si f c c
f b b d f b

which, using equ. (2.9), can be expressed as

B
R = R si − (R si − R ) ob f (2.12)
s
s
d
f
d
B ob
f

where
R si f = solution gas oil ratio of the bubble point oil, determined by flashing the oil
through the appropriate surface separators, and is measured relative to the oil volume
at 60°F and 14.7 psia (refer tables 2.3 and 2.4) (scf/stb).

R si d = solution gas oil ratio of the bubble point oil determined during the

differential experiment and measured relative to the residual oil volume at
60°F and 14.7 psia (refer table 2.5 and equ. (2.10)) (scf/stb-residual).

The differential data, as presented in table 2.5, can be directly converted to the
required form, table 2.4, using the above relations. For instance, using the following
data from table 2.5, at a pressure of 2400 psi

B o d = 1.2123 (rb /barrel of residual oil at 60°F and 14.7 psia)

R s d = 378 (scf/ —" — )

B ob d = 1.2830 (rb / — " — )

R si d = 540 (scf/ —" — )

while from the separator flash tests (table 2.3), for the optimum separator conditions of
150 psia and 80°F

B ob f = (1/ c ) 1.2511(rb / stb)
=
f b
R si f = 510 (scf / stb)

Therefore, using equ. (2.11)

1.2511
B = 1.2123× 1.2830 = 1.1822 rb stb
o

and equ. (2.12)

1.2511
R = 510 (540 378)× = 352 scf / stb
−
−
s
1.2830