In situ combustion and high-pressure air injection areenhanced oil recovery (EOR) processes used to recover oil from both heavy and light oil reservoirs. These processes, especially in situ combustion, are quite complex. In situ combustion involves consideration of heat and mass transfer, phase behavior of oil, water and gas, as well as relative permeability effects.
This paper outlines the 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 Saturates, Aromatics, Resins and Asphaltenes (SARA) fractions.
One outcome of the study indicated that saturates andaromatics 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, consistently with 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 maltenes and asphaltenes fractions were mathematically combined (per the mixing rule) to predict the actual observed HOC of the combined maltenes/asphaltenes 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 the other fractions.
In situ combustion and high-pressure air injection are technologies used for the recovery of both heavy and light crude oils. These technologies when used in tandem, involve thecreation of an oxidation front in the reservoir with subsequent propagation by air injection. Generally, air is injected in the reservoir and the oxygen contained in the air reacts with the oil through various oxidation reactions. The burning front is formed and the combustion gases produced from these reactions are available to help displace the oil. This process offers economic and technical opportunities for improved oil recovery in many reservoirs.
Many thermal analysis studies on both light and heavycrude oils have been conducted and several oxidation tests for modeling the process have been performed.
Verkoczy and Freitag(1) applied the relevance of various oxidation reactions to the modeling of in situ combustion inheavy oils, through three different sets of experiments. They performed thermal gravimetric scans and autoclave tests on three heavy oils and their SARA fractions. They found that low-temperature oxidation had significant and sometimes dramatic effects on the amount of coke formation. They also found that asphaltenes apparently underwent low-temperature oxidation more rapidly than other crude fractions.
K?k et al. ( (2) (used thermo gravimetric analysis under an air atmosphere at a 10 ° C/min heating rate. Two oils (medium and heavy) were separated into their SARA fractions. Then a quantitative investigation was performed in order to determine the temperature intervals at which evaporation, oxidation andcombustion effects operated for each fraction. Kinetic parameters of SARA fractions according to the Coat and Redfern technique were also established.
