Page 127 - Fundamentals of Reservoir Engineering

PVT ANALYSIS FOR OIL 66

In the presentation of differential data, in which volumes are measured relative to c ,
b
d
the values of v o and F in table 2.2 are replace by B and R where
o
s
d
d
B o d = Differential oil formation volume factor
(rb/stb-residual oil)
and R s d = Differential solution gas oil ratio

(scf/stb-residual oil)
Alternatively, by replacing c in equs. (2.5) and (2.6) by c , these parameters can be
f b b d
expressed as

v rb rb
B o d = c b o d stb residual rb b (2.8)
b
−

5.615 F scf
and R = R − (2.9)
d s si d c b d stb residual
−

where R is the initial dissolved gas relative to the residual barrel of oil at 60°F, and is
si
d
proportional to the total gas liberated in the differential experiment, thus
(Maximumvalueof F) scf
R si d = c b d × 5.615 stb residual (2.10)

−

and for the differential data presented in table 2.2

74.9557 5.615
×
R si d = .7794 = 540 scf stb residual oil
−
The majority of commercial laboratories serving the industry would normally present
the essential data in the differential liberation experiment (table 2.2) as shown in
table 2.5.

There is a danger in presenting the results of the differential liberation experiment in
this way since a great many engineers are tempted to use the B and R values
o
s
d
d
directly in reservoir calculations, without making the necessary corrections to allow for
the surface separator conditions. In many cases, the error in directly using the data in
table 2.5 is negligible, however, for moderate and high volatility oils the error can be
quite significant and therefore, the reader should always make the necessary
correction to the data in table 2.5 to allow for the field separator conditions, as a matter
of course.