Page 171 - Fundamentals of Enhanced Oil and Gas Recovery

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Thermal Recovery Processes

This process could be applied in high pressure shallow reservoirs. The temperature
of 400 600 C is required to run the CAPRI process [42,43]. As stated earlier, the

combustion front moves from toe of the well to its heel. This leads to occurring coke
lay-down. The deposited coke produces the required heat for the process by combus-
tion. The generated heat leads to reduction of heavy oil viscosity and its movement to
mobile oil zone in horizontal well. The following equations represent various com-
bustion reactions which occurs in ISC process [42,43]:
1. Thermal cracking (or pyrolysis):
Heavy residue-Light oil 1 Coke
2. Oxidation of coke (high temperature oxidation, HTO):

Coke 1 O 2 -CO 1 CO 2 1 H 2 O
3. Oxidation of heavy residue:

Heavy residue 1 O 2 -CO 1 CO 2 1 H 2 O
The process of oil upgrading is composed of two chemical reactions, namely,
addition of hydrogen and carbon rejection [44]. The latter causes thermal cracking
equation in THAI process. This reaction is a function of reservoir pressure and
temperature.
4. Carbon rejection:

CH x -CH x1 1 C ð x 1 . xÞ
The next step includes heavy oil pyrolysis accompanied by catalytic hydrogena-
tion using hydrotreating catalyst in CAPRI process as the following reaction:
5. Hydrogen addition:

CH x 1 H 2 -CH x1 ð x 1 . xÞ
Hydrogen containing products are produced during water gas shift reaction
and/or hydrocarbon gasification [45].
6. Gasification of hydrocarbon:
x
CH x -C 1
2H 2
ð
C 1 H 2 O steamÞ-CO 1 H 2
C 1 CO 2 -CO

7. Water gas shift:

CO 1 H 2 O-CO 2 1 H 2