Low temperature oxidation of heavy oil in oxygen-reduced air: Effect of pressure and oxygen content on heat release

Abstract

Air injection for in situ combustion (ISC) and air injection assisted cyclic steam stimulation (AACSS) techniques have a good application prospective in the development of heavy oils, while the explosion risk in the process of air injection is of great concern and has restricted the application of the technology. So that injection of oxygen-reduced air has been proposed to eliminate and control the explosion of oil/gas mixture with air. In this study, low-temperature oxidation experiments of heavy oil samples were conducted using a small batch reactor under the pressure of 5–15 MPa and oxygen content of 5%–15% at 225 °C in order to investigate the effect of oxygen content and pressure on the reaction rate and heat release during oxidation of heavy oil with oxygen-reduced air. The variations of temperature and pressure during the oxidation reaction were measured in the experiment, and the explosion phenomena of heavy oils were observed in the air with high oxygen contents (oxygen content more than 15%). The reaction rate and the exothermic heat of the reaction were calculated based on the pressure and temperature curves and using an improved heat loss model. The experimental results showed that reducing the oxygen content (e.g. reduced oxygen less than 10%) in air can effectively prevent the explosion of oil-gas mixtures, and the reaction rate and heat release during heavy oil oxidation are linearly proportional to pressure and oxygen content in the injected air when oil is in excess. The results of this study indicate that the heat generated in oil oxidation, which is important for the ISC and AACSS processes, can be controlled by pressure and oxygen content of the injected air, which can lay a good foundation for the oxygen-reduced air injection technique, especially for its application in deep heavy oil reservoirs, in which injection of oxygen-reduced air at high pressure can offset the effect of low oxygen content on heat release.