Study of the Effects of Low-Temperature Oxidation on the Chemical Composition of a Light Crude Oil

In this study, low-temperature oxidation (LTO) reactions of a light crude oil from the Daqing oil field at 175 and 225 °C were investigated and the changes of the composition and quantity of saturates, aromatics, resins, and asphaltenes (SARA) compounds, n-alkanes, terpanes, and steranes were analyzed, to determine the participation and generation of individual or groups of species in the LTO reactions. Pyrolysis experiments were conducted as a reference for heat effects. The results show that saturates and aromatics are converted to resins and asphaltenes. Both oxidation and heat effects in LTO reactions alter the distribution of n-alkanes, terpanes, and sterane. Oxidation effects cause the predominance of n-alkanes to shift to a lower carbon number, favor hopanes over tricyclic terpanes, and prefer high-molecular-weight steranes to lower molecular-weight ones. The changes of n-alkanes at higher LTO temperatures are controlled by oxidation effects. For terpanes and steranes, heat effects gain dominance at higher LTO temperatures.