Chemical-structural properties of the coke produced by low temperature oxidation reactions during crude oil in-situ combustion

Chemical-structural properties of the coke produced by crude oil low temperature oxidation (LTO) reactions during in-situ combustion are still highly lacking due to the difficulty in coked sand characterization. This study proposed an experimental methodology to prepare the useful LTO coke with the chemical-structural properties studied using a combination of Energy-dispersive X-ray spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. The XRD and the HRTEM analyses showed the LTO coke mainly consisted of highly disorder amorphous structures with limited amount of poorly order ‘onion-like’ structures. The LTO coke was found to contain numerous oxygen functionalities and highly-substituted aromatic rings. The concentration of the carbonyl showed no significant decline with the LTO temperature increasing to 310 °C. Nevertheless, the carbon structure with sp³-rich characteristics was found to selectively consumed by O₂ to reduce the amount of coke deposition, and enriched the aromatic layer systems as inferred by Raman and FTIR analyses. There was a good agreement between the amount of the ‘onion-like’ structures viewed from HRTEM and the changes in the ether bridging groups. Additionally, the changes in the coke chemical-structural properties agreed with the measured coke reactivity by Thermogravimetric analyses.