Page 96 - Fundamentals of Enhanced Oil and Gas Recovery

84 Ramin Moghadasi et al.

3.2.2.2.10 Chung et al. [40]
Chung et al. [40] developed a correlation for viscosity prediction of CO 2 /heavy
oil mixtures. In general, they stated: “the viscosity of CO 2 /heavy oil mixture is a func-
tion of composition. This composition-dependent function is extremely complex for CO 2 /
heavy oil mixtures.” Due to this fact, they suggested to treat the mixture as a binary
system with two components: pure CO 2 and heavy oil. Based on experimental
results, they also concluded that the viscosity change of heavy oil is related to the
quantity of CO 2 dissolved in the oil. Finally, they developed a model for predict-
ing the viscosity of CO 2 -satuated mixtures while the concentration of CO 2 in the
oil and viscosities of both CO 2 and oil are known. Chung et al. [40] used the
Lederer [51] equation as the basic formulation to their model. The formulations
are as follows [40]:
ln μ 5 X o ln μ 1 X s ln μ s (3.19)
m
o
with

V s
X s 5 (3.20)
αV o 1 V s
and
X o 5 1 2 X s (3.21)
where V is volume fraction; μ is viscosity in mPa.s; and the subscripts m, o, and s
stand for mixture, heavy oil, and CO 2 , respectively. In Eq. (3.20), α is an empirical
constant that can be determined by Eq. (3.22) as follows:
7:36
e 2 e 7:36ð12p r Þ
α 5 0:255γ 24:16 T 1:85 (3.22)
r 7:36
e 2 1
where T r 5 T/547.57 and p r 5 p/l071 are reduced temperature and pressure, respec-
tively; T is temperature in R; and P is pressure in psia.

The volume fraction of CO 2 in the mixture can be obtained from the CO 2 solu-
bility or swelling factor according to their definitions. Accordingly, X s can be calcu-
lated by Eq. (3.23) as follows:
1
X s 5 (3.23)
αF CO2 = F o R s Þ 1 1
ð
where F CO2 is the ratio of CO 2 gas volume at standard conditions to the volume at
system temperature and pressure, and F o is the ratio of oil volume at system tempera-
ture and 1 atm (0.101 MPa) to the volume at system temperature and pressure. It
must be noted that for viscosity calculation, one needs to determine the CO 2 viscosity
(μ ) at the specified temperature and pressure conditions. Chung et al. [40] have
s