Page 142 - Fundamentals of Enhanced Oil and Gas Recovery

130 Pouria Behnoudfar et al.

CO 2 solubility depends mostly on temperature, pressure, and specific gravity of the oil. A
correlation for solubility of CO 2 in heavy oil is given by the followings [67]:
1
R s 5 (4.46)
a 1 γ 2 T 7 1 a 3 T 4 exp 2 a 5 p 1 a 6
a
a
a
p
where γ is the specific gravity of heavy oil, T is temperature in F, p stands for pres-

sure in psia, and R s indicates the solubility of CO 2 in a crude oil in scf/bbl. The
empirical constants a 1 through a 7 are 0.4934E 2 2, 4.0928, 0.571E 2 6, 1.6428,
0.6763E 2 3, 781.334, and 20.2499, respectively. The above correlation can approxi-
mate the CO 2 solubility for pressures below 3000 psia.
The swelling factor (F s ) is defined as the ratio of the volume of CO 2 -saturated oil
at the temperature and pressure of the reservoir to the volume of the dead oil at reser-
voir temperature and atmospheric pressure [120]. The magnitude of swelling for hea-
vy oil is not as drastic as for light oil, which can be swelled more than two times of its
original volume. The following correlation for determining swelling factor could be
proposed as follows [120]:

0:35R s
F s 5 1 1 (4.47)
1000
In above equation, R s and F s denote, respectively, CO 2 solubility in crude oil (in
scf/bbl) and swelling factor as ratio. In general, viscosity of CO 2 /heavy-oil mixture is
a function of composition. This composition-dependent function is extremely com-
plex for the CO 2 /heavy-oil mixtures due to the fact that it is not possible to reach
the detailed composition of heavy oil and the contribution of each component to the
viscosity of the mixture cannot accurately be determined. Hence, the CO 2 /heavy oil
mixture is treated as a binary system with two components [5]:
• Pure CO 2
• Heavy oil
Chung et al. [67] stated that the viscosity variation of heavy oil is related to the
quantity of CO 2 dissolved in the oil. Therefore, if the concentration of CO 2 in the
oil and both the viscosities of CO 2 and heavy oil is determined, a relationship can be
obtained to estimate the viscosity of the CO 2 /heavy-oil mixture.
The viscosity ratio between the two components of this system (i.e., heavy oil and
CO 2 ) is in the range of 103 106. The following equation can be utilized in such
high ratio of viscosity combinations [121].

lnμ 5 X 0 ln μ 1 X s ln μ (4.48)

m 0 s
where
V s
X s 5 (4.49)
αV o 1 V s