Updated understandings on coke formation during the inferior heavy oil in-situ combustion process: A combined FTIR, XPS, TG/DTG, and DSC study

Low temperature oxidation (LTO) had a considerable contribution on coke deposition and corresponding structure evolution during heavy oil in-situ combustion (ISC) process. Therefore, elemental analysis, Fourier transform infrared spectrophotometry (FTIR), X-ray photoelectron spectroscopy (XPS), synchronous thermal analysis (TG/DTG-DSC) experiments, and different model-free methods were jointly employed for LTO cokes to trace features of main elements and functional groups and to characterize non-isothermal oxidation characteristics and kinetics. It was shown that there were superior intensities of hydrogen bonds and “coke peak” for coke LTO2 , formed under a superior oxidation condition. Besides, C-H bonds were mainly converted to C-O groups, and then evolved into C = O, which was the precursor of C = C. Moreover, TG/DTG-DSC analysis indicated that a drastic combustion process was observed for both cokes with lower threshold and peak temperatures and higher exothermic peaks, compared with the heavy oil. And it was further verified via the distribution of activation energy variation with conversion determined by Friedman and DAEM methods. Furthermore, Pearson's correlation analysis lent further support to these kinetic findings. From this study, it could provide updated understandings on the LTO importance in the coking mechanism and structural feather during ISC process.