Influence of in situ fuel deposition on air injection and combustion processes

Sustained propagation of a combustion front is necessary for improved oil recovery during an air injection and in situ combustion process. The front is a sharp diffusive layer and involves the added complexities of reactions. In this work, the combustion front is represented by two oxidation reactions: a high-temperature fuel burning reaction and a low-temperature fuel generating reaction. Due to distinct reaction kinetics and stoichiometry, the reactions occur in sequential regions within a finite separation distance in the reservoir. Interaction of these regions and its overall influence on the front propagation are investigated locally using an analytical approach based on large activation energies of the reactions. Reservoir conditions under which the regions could travel with a common propagation speed is identified and their limits of coherence are investigated in the presence of external heat losses. Consequently, a new intricate relationship between the reservoir heat loss rate and separation distance of the reaction regions is found and formulated. The regions propagate closely spaced, thus minimizing the influence of deleterious heat losses and improving the combustion process performance. This two-reaction self-sustainability mechanism keeps the combustion front propagating steadily, even though under the same conditions front extinction has been predicted for the equivalent single-reaction problem. The work emphasizes the importance of local nonlinear chemical processes during air injection.