Abstract: The process of coke generation of naphthenic heavy oil during air injection combustion was studied to clarify the law of coke generation and the basic properties of petroleum coke in the fire flooding process of naphthenic heavy oil, and the composition and structure of generated petroleum coke were characterized through a dynamic airflow oxidation crude oil device. The study showed that the coke generation from naphthenic heavyoil starts at about 250-300 ℃, and the coke yield increases gradually with the rise of the reaction temperature and the highest coke yield of 10.8% is obtained when the temperature reaches 450 ℃; the combustion reaction of coke intensifies, and the yield decreases to 4.6% when the temperature is 500-600 ℃. The coke is observed as a dense lamellar structure with 0.05-1.00 μm carbon layers superimposed on each other by electron microscope, and it could be classified into two categories with 400 ℃ as the demarcation point. The H/C atomic ratio of coke generated is 0.78-0.82 at 300-350 ℃, which is oxidized coke containing many alkyl chains. The cracking reaction intensifies at 400 ℃, and the process of heavy oil coke formation transforms from the primary oxygenation reaction to that of cracking, and most cokes generate at 400 ℃. The H/C atomic ratio of the coke generated at 400-600 ℃ is 0.33-0.47, which was cracked coke with higher aromaticity and graphitization degree. This study is of some significance for the ignition and fireline control during fire flooding development of naphthenic heavy oil.

Key words: fire flooding, in-situ combustion, coke, low-temperature oxidation, high temperature oxidation, cycloalkyl, physicochemical characteristics