A two-dimensional compositional simulation of the in situ combustion process
A numerical model for simulating a dry forward in-situ combustion
process in two dimensions, was developed. The primary focus is on the
simulation of the compositional changes that take place inside the porous
medium during the running of the process. The model allows any
number of hydrocarbon components and six others, namely, liquid water,
water vapour. oxygen, nitrogen, carbon dioxide, and carbon monoxide. It
describes the flow of water. oil, and gas, and includes the gravity and
capillary effects. The vapourisation and condensation effects of both
hydrocarbons and water enhanced the heat transfer, primarily by
conduction and convection, ahead of the combustion front.
Equilibrium calculations are performed on the components in both the
liquid and vapour phases. The changes in pressure, temperature, and flUid
compositions govern the direction of the interphase mass transfer.
Heat is generated by two types of reaction, namely, low temperature
oxidation and burning of the crude oil. The model allows the movement
of a thin burning front inside the burning cell. It is found to give a better
temperature profIle. representative of the combustion process.
Oxygen mole fraction is calculated throughout the porous medium
according to the reaction kinetics. thus no assumption is made regarding
the degree of oxygen consumption. The effects of oxygen bypassing
caused by the kinetic-limited combustion is therefore represented.
A total of 18 components were used in the computer runs. Results show
the preferential vapourisation of the lighter components in the vicinity of
the high temperature burning front. The lighter components then move
towards the producer. faster than do the heavier ones. This segregation
produce fuel that is heavier than the original oil.
High temperature in the upstream cells causes a reduction in the oil
viscosity. which in turn increases its mobility, thus transporting more
heat downstream. The rise in temperature in the condensation cell results
in a decrease in the rate of water vapour condensation; extending the
condensation zone downstream.
In the high pf(>ssure run. all the hydrocarbon in the downstream cells
condenses. In the burning cell however. both the vapour and the liquid
phases are present due to the high front temperature. The vapour phase is
richer in the light components while the liqUid is richer in the heavy