Page 86 - Primer on Enhanced Oil Recovery

Thermal EOR 77

Figure 8.10 Zoning for wet forward burning.

eventually just lost. Additionally, almost 40% of costs are related to the air injec-
tion into the formation. All this increases recovery expenses. It is possible to reduce
those problems if the heat conductivity of gases is increased. This can be done if
one adds something to provide heat conductivity and/or transport. It is possible to
use water. On those grounds technology of wet forward combustion has been devel-
oped. Water then either injected together with air or sequentially. Water evaporates
in zone 1 and transfers heat beyond burning zone. It is possible then identify five
zones, as on Fig. 8.10
Zone 1 does not contain almost any hydrocarbons. This zone is saturated with
water and oxygen. As temperature is below water boiling point, the zone contains
much of liquid water.
Zone 2 has all water in vapor form. The line of full water evaporation divides
zone 1 from zone 2.
Zone 3 is burning zone. Burning consumes all hydrocarbons, including unmov-
able coke.
Zone 4 encompasses both evaporation and condensation. Temperature in this
zone is close to water evaporation at the same time condensation of water from
burning products is taking place. Light fractions of oil evaporate. On the border
with zone 3 partial hydrolysis takes place.
Zone 5. Contains main water and oil volume. Temperature and pressure are close to
the formation original. The mobile hydrocarbons are moving towards production well.