Formation and Combustion Heat Release of Naphthenic-Based Crude Oil Cokes at Different Reaction Temperatures

Petroleum cokes prepared from naphthenic crude oil differ significantly in terms of the oxygen content and hydrogen/carbon (H/C) ratio, which mainly depend on the different coking temperatures. Thermogravimetric-differential scanning calorimetry was applied to study the heat release and combustion weight loss of petroleum cokes prepared at 350 and 500 °C, respectively. The effect of different coke formation temperatures on the combustion properties of the coke formed during air injection in situ combustion (ISC) was also investigated. The results showed that the petroleum coke formed under oxygen exhibited an H/C ratio of 0.895 and an O/C ratio of 0.109 at 350 °C and an H/C ratio of 0.395 and an O/C ratio of 0.054 at 500 °C. As the temperature rises, the hydrogen atoms on the petroleum coke molecules intensify to separate and form water molecules and thus giving off heat. It can be further inferred that under the combustion temperature of air injection ISC, the coke at 350 °C can release more heat in the lower combustion temperature range, and the combustion weight loss is faster; however, the formation temperature continues to rise due to combustion at 500 °C, coke begins to release massive heat, and the combustion weight loss is as high as 97.95%. The combustion residuals of both temperature cokes and the residual solid content of the formation after combustion in porous media are both little, which can be used as fire flooding fuels at different formation temperatures to provide heat energy for oil displacement.