Integrative Investigation of Low-Temperature Oxidation Characteristics and Mechanisms of Heavy Crude Oil

During an in situ combustion (ISC) process, low-temperature oxidation (LTO) is of vital significance for the follow-up oxidation reactions and oil recovery. Herein, this work is intended to carry out in-depth investigations regarding LTO of heavy crude oil. Alterations of evolved gas compositions and oil properties caused by LTO were first examined. Then the particular focus was placed on the analyses of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) of oxidized oil samples. The results indicated that the LTO degree was intensified with the oxidation temperature, during which produced gas compositions and the contents of element, saturates-aromatics-resins-asphaltenes (SARA) fractions, free radicals, and hydrogen groups of oils changed obviously. Furthermore, part of the main LTO reactions are given in this paper. On the basis of these reactions and experimental results obtained, some aspects of LTO mechanisms of the oil are stated, which were highly valuable for ISC field applications.