Thermo-oxidative characteristics and kinetics of light, heavy, and extra-heavy crude oils using accelerating rate calorimetry

Abstract

The thermo-oxidative characteristics and kinetics of crude oil directly affected the combustion performance and oil upgrading. This paper brought an in-depth analysis regarding quasi-adiabatic oxidation of crude oil that was still less well-understood. Firstly, the thermo-oxidative characteristics of light, heavy, and extra-heavy oils were studied using accelerating rate calorimetry (ARC). The thermo-oxidative kinetic analysis was then conducted. Particular emphasis was put on the differences into the auto-ignition temperature, exothermic extension of reactions, and kinetic parameters of heavy and extra-heavy oils, with the intent of achieving stable combustion and heavy oil upgrading. The results showed that the light oil encountered heat release triggered by low-temperature oxidation at the reservoir pressure and temperature (7.8 MPa and 95 °C), and its self-ignition temperature was determined to be 100 °C. A continuous heat release was observed in the entire oxidation process, suggesting the air injection might be appropriate for the light oil reservoir. There was no self-exothermic signal at the reservoir pressure and temperature (6.3 MPa and 35 °C) during heavy oil oxidation, and the onset self-exothermic oxidation temperature was found to be 50 °C. Compared with heavy oil, the extra-heavy oil had the obviously higher onset self-exothermic temperature and auto-ignition temperature. This meant that higher ignition temperatures and more lasting ignition time were required when considering in-situ combustion (ISC) of extra-heavy oil. According to the ARC results obtained, we suggested that the near-wellbore areas of the heavy and extra-heavy oil reservoirs were heated up to 120 and 180 °C, respectively. In this scenario, a large amount of heat could be released due to oil oxidation, thereby causing highly efficient upgrading of heavy oil. Additionally, the values of activation energy further confirmed that the heavy oil could be oxidized more easily compared to the extra-heavy oil. The oxidation reactions of heavy oil were less concentration-dependent in comparison with light and extra-heavy oils, indicated by the reaction order. Some new insights derived from this study facilitated achieving rapid and stable combustion, resulting in crude oil upgrading.