Thermal Analysis and Combustion Kinetic of Heavy Oils and Their Asphaltene and Maltene Fractions Using Accelerating Rate Calorimetry

This work presents an experimental study on the thermal and kinetic parameters of the oxidation reaction of heavy crude oils to support the in-situ combustion oil recovery technique. An accelerated rate calorimeter was used to investigate the thermal behavior of two Brazilian heavy oils in an open system under constant pressure and continuous heating to 550 degrees C. The goal was to identify and characterize several oxidation regions and to obtain the activation energy and reaction order. The temperaturetime curves showed three clearly distinct regions. During the heating, autoignition was found to have started at 180-220 degrees C. Then, the reaction curves exhibit a strong exothermic behavior up to 250-350 degrees C, which represents the low-temperature oxidation. Asphaltenes were found to play a crucial role in the kinetic behavior of the crude oils. The results show that oxygen-addition reactions are dominant from 200 to 300 degrees C and that bond-scission reactions are dominant above 350 degrees C. Although the presence of sand and clay improves the contact between the oil and oxygen and accelerates both of these reactions, it has a greater impact on the oxygen-addition reactions. The results provide helpful data for the screening of crude oils as candidates for recovery by in-situ combustion.