Page 85 - Fundamentals of Enhanced Oil and Gas Recovery

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Enhanced Oil Recovery Using CO 2

where a and b are the constants of PR equation, x represents the mole fraction of
each component in the mixture, δ is the binary interaction parameter, a i,j and b i are
also constants that are functions of critical pressure and temperature, and acentric
factor.
Using PR EOS, Mulliken and Sadler [38] showed that it is possible to treat the oil
as a single pseudo-component. Finally, they were able to characterize the system of
CO 2 oil only when specific gravity, mean boiling point, or UOP factor is known.
They used the same experimental data of Simon and Graue [37] for accuracy evalua-
tion. Their model showed an average error of only 1.9% in the predicted CO 2 mole
fraction in the oil; thus it shows better performance as compared with the
Simon Graue [37] correlation, which gives an average error of 2.3%.

3.2.2.1.3 Mehrotra and Svrcek [39]
They proposed a new correlation for prediction of CO 2 solubility, mainly in bitumen.
However, their correlation has been applied for crude oil samples. They found a linear
relationship between pressure and CO 2 solubility up to a pressure of about 6 MPa.
Beyond this region predicted values deviate much from experimental data. This is
indeed a limitation to the use of their correlation. Temperature range was also set to

be from 23.89 C to 97.22 C. An average deviation of 6.3% is reported for their cor-
relation. The correlation is as follows:
2
P P
3 3
Solubility ðcm CO 2 =cm mixtureÞ5b 1 1 b 2 P 1 b 4 1 b 4 (3.4)
T T
with
b 1 52 0:0073508; b 2 52 14:794; b 3 5 6428:5; and b 4 5 4971:39

where T is in K and P is in MPa.

3.2.2.1.4 Chung et al. [40]
Chung et al. [40] defined the solubility of CO 2 in a crude oil, R s , as the volume (in
scf) of CO 2 in the CO 2 -saturated oil per barrel of dead-state oil at the temperature at
which solubility is measured. They stated that CO 2 solubility mostly depends on tem-
perature and pressure and only slightly on specific gravity. Referring to the proposed
solubility diagram as a function of pressure by Chung et al. [40], they postulated the
following discussions about CO 2 solubility.
“As demonstrated in the solubility diagram developed by Chung et al. [40], sol-
ubility of CO 2 in heavy oil increases with pressure but decreases with temperature at pres-
sures below 3000 psia. The line of the 75 F(24 C) isotherm shows that solubility of

liquid CO 2 (at pressures greater than 1000 psia (6.9 MPa)) in oil is not strongly sensitive
to pressure. The solubilities of gases in liquids are normally decreased with the increase of