In-Situ Combustion With Oxygen-Enriched Air

Abstract

ABSTRACT To evaluate the field of application of in—situ combustion with oxygen, research was performed on the specific characteristics of in—situ combustion with oxygen-enriched air as compared to conventional combustion with air using two oils having different specific gravities (0.90 and 0.96). The equipment is made up of an outer cell and an inner tube, equipped with heating collars. Since extensive safety precautions must be taken when using high oxygen concentrations, special attention was devoted to the choice of materials and equipment when the device was being designed. The device is combined with a computerized control system (flowrates, pressures, heat losses control) as well as data acquisition and processing of the experimental results. The effects of total pressure, oxygen partial pressure and injected oxygen flux were studied. When the total injected flux (N2+O2) is constant and oxygen partial pressure increases, there is a less than proportional increase of the combustion front velocity no matter what pressure and oil are considered. This result is due to insufficient residence time of the oxygen in the reaction zone when the oxygen flux becomes very high. The results obtained at low pressure (1 MPa, 145 psi) at a constant oxygen flux show that the fuel availability and the air requirement at front are slightly affected by the oxygen partial pressure. Indeed, a slight increase in these parameters is found with oxygen enrichment for the heavier oil, and the opposite effect for the lighter oil. When the oxygen concentration increases at higher total pressure (7 – 10 MPa, i.e. 1015–1450 psi) and at constant oxygen flux, the characteristics of combustion are hardly affected for the heavier oil, whereas a reduction of about 40% is observed for the oxygen requirement at front for the lighter oil. These results can be explained by heat–exchange and mass –transfer phenomena. Combustion tests performed in sand packs that had first been swept by carbon dioxide, so as to simulate its effect in the zones downstream from the oxygen combustion front, revealed the influence of this gas on the process. This laboratory study allowed us to compare the performances of combustion with enriched air in relation to those of conventional combustion with air. The results showed, in some cases, the advantage that can be obtained by using a gas richer in oxygen than air.