Thermo-oxidative behavior and kinetics analysis of light and heavy oils based on TG, DSC, and FTIR

Abstract

In-situ combustion (ISC), as a time-honored replacement technology for heavy reservoir development, needs to improve its application effect urgently. The oxidation exothermic behavior and reaction activity of heavy oil directly determine the EOR effect of ISC technology during air injection. In this work, the oxidation heat effect and combustion activity of light and heavy crude oils, and the physical properties of their oxidized oils were studied and compared through thermogravimetry (TG), differential scanning calorimetry (DSC), static non-isothermal oxidation and Fourier transform infrared spectroscopy (FTIR). The results indicate that the main reaction pathway of MH light oil is distillation and volatilization under 200 °C, the mass loss is obvious and the heat release is more than that at the high temperature oxidation (HTO) stage. After the full reaction of FC heavy oil at 350 °C, there is still about 30% low temperature oxidation (LTO) left. After the LTO and fuel deposition (FD) stages, heavy oil can produce more coke. MH light oil and FC heavy oil show an obvious mass loss at the stage of LTO and HTO, which is 68.8% and 27.3% (10 °C/min) respectively, the corresponding enthalpies are 3.02 kJ/g and 15.668 kJ/g as well. Between 470 and 500 °C, the endothermic reaction of heavy oil becomes weak, which may relate to the condensation of heavy components such as resins that release heat. The LTO activation energy of light oil decreases with the conversion, and temperature increase can promote the oxidation reaction of active components. The LTO activation energy of heavy oil increases with the conversion, while that in FD and HTO stage increases obviously, which indicates that coke combustion activity is low. The content of C1–C6 in heavy oil decreases from 5.81% to 3.57% with heating rates. The oxidation reaction in the full temperature range can improve the quality of heavy crude oil. The vibration peak at 1707 cm-1 of the MH oxidized oil gets weak, the vibration peak at 1539 cm-1 disappears, and the number of carboxyls, ether groups, aromatic rings, and miscellaneous molecules in the oxidized oil declines. The vibration peak at 3460 cm-1 of the oxidized oil enhances significantly, and the number of carboxyls and hydroxyl molecules increased.