Page 93 - Fundamentals of Enhanced Oil and Gas Recovery

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Enhanced Oil Recovery Using CO 2

favorable toward a higher sweep efficiency. In addition, it is interesting to note that

CO 2 effects on viscosity reduction are minimal at temperatures above 150 C, because
at this temperature solubility of CO 2 experiences large decreases.
A number of correlations can be found in literature, which are applicable for vis-
cosity calculation of crude oils mixed with a gas (e.g., CO 2 ).

3.2.2.2.6 Welker and Dunlop [43]
They presented a graphical method for viscosity prediction of carbonated crude oils.
They first designed an experimental setup, and based on the original Darcy’s equation,
developed their model of viscosity prediction. The setup basically consisted of a
small-diameter steel tube, pressure gauges, flow controllers, and inlet outlet accumu-
lators. A detailed description of their setup has been given in their chapter. Having
laminar stabilized flow rates, finally, they were able to measure the viscosity of differ-
ent crude oil CO 2 solutions. Fig. 3.11 shows the results of experiments conducted
by Welker and Dunlop [43]. As it can be seen in this figure, they presented viscosity
ratio values instead of viscosity itself. Indeed, such a presentation would give a good
understanding of viscosity reduction due to CO 2 dissolution in crude oil. Based on
this figure, they found that viscosity reduction is much more pronounced for those
crude oils with a high dead oil viscosity. For this statement to be clear, consider a
high viscosity oil (e.g., μ 5 1000 cP) and a low viscosity one (e.g., μ 5 40) both being
kept at pressure of 200 psia. Based on Fig. 3.11, the viscosity has reduced to about
25% of dead oil viscosity for the high viscosity oil, while this reduction is read to be
about 45% for low viscous one.
Welker [43] also stated that the viscosity reduction using dissolved CO 2 is greater
than that for natural gas or pure methane (Fig. 3.12). This means that a higher

Carbonated µ c / dead oil viscosity (µ o %) 30 400
200 psia
50

600
800
10

2 10 40 100 400 1000 4000
Dead oil viscosity, (cP)
Figure 3.11 Viscosity reduction of carbonated oils at 80 F [43].