Investigations of Structure-Property-Thermal Degradation Kinetics Alterations of Tahe Asphaltenes Caused by Low Temperature Oxidation

In situ combustion (ISC) is advantageous for (ultra)heavy reserves due to its high heating efficiency and small surface footprint compared to steam injection. Herein, the focus of this work was given to the key factor in sustaining the continuity of the combustion front, the asphaltene fraction. Structure-property alterations of Tahe asphaltenes caused by low temperature oxidation (LTO) were thoroughly examined. Particular attention was placed on its combustion and pyrolysis kinetics. The results showed that after LTO 10.35 wt % coke was formed. Scanning electron microscopic observations indicated that the surfaces of the oxidative products were fairly rough as a result of air attack and the caused reactions on site, and these alterations promoted the subsequent combustion. The textures of the products were observed to be further compacted and condensed after LTO. As anticipated, distinguished reaction regions were clearly identified on the thermogravimetric (TG)/differential scanning calorimetric curves in this work. The results of TG and activation energy revealed the differences of the reaction sites in the combustion and pyrolysis processes. The coke formed after LTO exhibited the highest reaction activity and exothermic effect compared to the fresh asphaltenes and residue. It is believed that this work can add new insights to ISC with regard to the mechanisms and reaction models, which are highly valuable for field applications.