Page 132 - Primer on Enhanced Oil Recovery

122 Primer on Enhanced Oil Recovery

Figure 10.26 Gas cap displacement.

Figure 10.27 Gas condensate pressure maintenance.

out at fields with a reservoir pressure close to the pressure of the onset of condensa-
tion, high rate of liquid precipitation during condensation (20 40% of the pore vol-
3
3
ume) and with a significant condensate yield of at least 10 23 m /m .
Miscible displacement. The miscible displacement of oil during the injection of
high-pressure nitrogen is provided by the evaporation of intermediate hydrocarbons
from oil and their dissolution in nitrogen. This forms a transition zone mixing, con-
taining a mixture of nitrogen and intermediate hydrocarbons, which is soluble in
oil. This process effectively displaces oil to producing wells (Fig. 10.28).
In some cases, after the injection of nitrogen a slug of water is injected.
Eventually, this forms a slug with nitrogen/water mixture. It has been shown to pro-
vide an efficient oil displacement of oil (Fig. 10.29).
Gravity drainage is used in reservoirs with the good potential for the nitrogen
injection process due to the large depth or strata inclination. Nitrogen, which has a
lower density than the reservoir oil, when it is introduced into the top of the reser-
voir, will displace the oil under it (see Fig. 10.30). In this case the displacement is
piston-like without any displacement front viscosity instabilities. In this case the
greater the slope the higher is interface stability. The gas distribution is