Page 87 - Primer on Enhanced Oil Recovery

78 Primer on Enhanced Oil Recovery

Figure 8.11 Zoning for reverse combustion.

8.2.1.1.2 Reverse combustions
Zone 1 near injection well is considered to be in as-formation conditions prior to
air (oxidant) injection. However, if oil is easily oxidized, this can lead to slow
increase of temperature following beginning of the injection (Fig. 8.11).
Zone 2 includes formation with steeply rising temperature due to heat transfer
from burning zone. The heat is railed by hot gases and water vapor from burning
zone. The zone is also significantly enriched by light oil fractions distilled from the
burning zone. Oil light and mobile fractions are displaced. Some amount of coke is
also created.
Zone 3 is burning zone. Temperature is at its maximum. Burning consumes all
available oxygen. As the rule only most reactive hydrocarbons oxidize.
Zone 4 can be characterized by well separated hydrocarbon and water fractions.
Due to thermal losses to the surrounding rock, the temperature in this zone decreases
with the distance from burning zone. The decrease rate depends on water and light oil
fraction condensation conditions. Produced during burning coke is immobile while
light oil fractions and water are very mobile and can be easily extracted.

8.2.2 Screening criteria
In situ combustion is applicable to wide type of oil reservoirs (Fig. 8.12). In general
terms ISC application conditions, e.g. application boundaries, are identical to steam
injection. Oil properties, formation depth, possible amount of energy produced and
ability to collect processed oil need to be carefully considered.