Heats of Combustion of Selected Crude Oils and Their SARA Fractions

Abstract

In situ combustion and high-pressure air injection are enhanced oil recovery (EOR) processes used to recover oil from both heavy and light oil reservoirs. These processes are quite complex and involve consideration of heat and mass transfer, phase behaviour of oil, water and gas, as well as relative permeability effects. This paper outlines a study that was conducted in order to develop a better understanding of the heats of combustion (HOC) for three different types of crude oils and their respective saturate, aromatic, resin and asphaltene (SARA) fractions. One outcome of the study indicated that saturates and aromatics have higher heating values than resins and asphaltenes, where this value in both saturates and aromatics (in any given crude oil) is close. Resins and asphaltenes also displayed heating values that were almost the same, however, were consistent in having a lower heating value than saturates and aromatics. The linear mixing rule was applied to predict the heat of combustion for the three crude oils studied. The HOCs for the maltene and asphaltene fractions were mathematically combined (per the mixing rule) to predict the actual observed HOC of the combined maltene/asphaltene crude. This rule did not hold true for all the crude oils studied, however, which suggests that the heat of combustion is not necessarily independent of the presence of other fractions.