Forward in-situ combustion : Real-time mass and energy balances, reaction kinetics and control
Enhanced oil recovery by dry forward in-situ combustion has
been studied in a combustion tube. Twelve experiments are
reported exploring the effects of three factors: oxygen flow,
partial pressure and mole fraction, each factor at two levels.
The pressures used went up to 790 kPa, and the oxygen mole
fraction to 35%.
It was discovered that the oxygen partial pressure had no
statistically significant effect. The oil recovery was
independent of the factors used. The combustion time was
dominated by the oxygen flow, as were the reaction rates, while
fuel and oxygen consumption depended mainly on the oxygen mole
fraction. Increasing the oxygen mole fraction reduced the
consumption figures. The reaction stoichiometry was substantially
independent of the three factors. It was also found that the
total pressure had no statistically significant effect on oil
recovery, combustion time, reaction rates, fuel consumption or
The oil produced by the in-situ combustion process tended to
be of lower viscosity and density than the original oil.
Oil-water emulsions were produced which could not be broken.
The experiments were controlled by a computer, and the PID
control algorithms and associated equipment proved succesful.
Linked in with the control routines was a model of the process to
calculate fluid saturations and flows during the course of the experiment. Measured information was used directly in the mass
and energy balances. The resultant fluid saturations supplied a
reasonable match with experimental oil saturations from two
experiments that were stopped early. The computed liquid
production histories also matched up well with the experimental
The oil saturations from the numerical model were used in
developing a robust method for calculating reaction constants
from the experimental data. A simplified surface-reaction scheme
was used involv~ng low-temperature oxidation and fuel burnoff to
explain the effects of flow, pressure and oxygen mole fraction on