Isothermal oxidation behavior of heavy crude oil and its low-temperature oxidized oils: Implications for in-situ upgrading of heavy oil

Abstract

Oxidation of heavy oil is essential for the success of in-situ combustion (ISC) projects. However, the isothermal oxidation behavior of heavy oil has not been well understood. In this work, the static oxidation experiments at temperatures of 80, 120, 160, and 200 °C were conducted to obtain the low-temperature oxidized oils (LTOO). Subsequently, the heat release caused by oxidation reactions of heavy crude oil and its LTOO at temperatures of 100, 200, 300, 400, and 500 °C was thoroughly examined. The results indicated that heavy crude oil was subjected to heat release yielded by low-temperature oxidation (LTO) at 100 °C. At the initial oxidation stage, the peak heat flow at 400 °C for heavy crude oil was obviously greater than that at 500 °C, different from the cases of the other four oxidized oils. For all the heavy oils used, the combustion at 400 °C produced a more lasting thermal effect than that at 500 °C. All the heavy oils used showed similar exothermic behavior at 100 and 200 °C. But at 300 °C, the LTO of the oil oxidized at 160 °C released more heat in comparison with that of the oil oxidized at 200 °C, which was thought to be caused by the saturate and aromatic components present in these two oxidized oils. Compared to the other four heavy oils, the combustion at 400 °C for the oil oxidized at 200 °C released fairly higher heat. However, there were minor differences in the isothermal DSC curves at 500 °C for all the heavy oils, indicating that LTO reactions at temperatures no greater than 200 °C produced negligible influence on heavy oil combustion at 500 °C. For this reason, a reasonable increase in the ignition temperature was recommendable when achieving ISC of heavy oils with deep LTO degrees and ultra-heavy oils.