Abstract

Although many thermal analysis studies on both crude oils and oil-rock mixtures had been conducted, the fundamental and critical researches on oxidation and ignition behavior of pure hydrocarbon components of crude oil fractions under an oxidizing atmosphere are not documented before. This research is aimed at providing better understanding of oxidation behavior of fractions of crude oil, and then finds out an approach to improve ignition and accurate modeling for air injection processes by using the effects of individual fractions on whole oil combustion.

In this research, Thermogravimetric and Differential Thermal Analysis techniques, TG/DTG and DTA investigations on thermal fingerprinting effects of each pure paraffin sample, mixtures of different pure samples, and mixture pure samples with crude oil, on oxidation and ignition behavior were conducted. The results demonstrated that different paraffin samples show a great different contribution to low temperature oxidation reactions, high temperature oxidation reactions and heat generated. The fractions lighter than C16 will distillate before they reach low temperature oxidation reaction. Only low temperature exothermic activities are apparent for the fractions between the fractions between heavier than C16 and lighter than C26. The C26 and heavier fractions show both low and high temperature exothermic activities. Paraffin samples mainly contribute to low temperature exothermic activates, released more heat in low temperature ranges. The lower molecular weight sample shows lower onset temperature of oxidation reaction and show very rapidly reaction rate. With increasing of molecular weight, the exothermic peak temperatures both in low and high temperature regions shift to higher temperature, and more heat value released.

When unreactive Oil B and reactive Oil C was mixed with a small amount of paraffin sample heavier than C26, both the crude oils of low temperature oxidation behavior can be intensified, with a greater magnitude of heat evolution, which is of potential to accelerate reaction and improve ignition.

Introduction

Air injection has been proven as a potential and viable process in improving oil recovery from several light oil reservoirs. When air is injected into an oil reservoir, the oxygen contained in the air reacts with the hydrocarbon in place, by various oxidation reaction schemes. Success of such a process depends mainly on the crude oil properties and rock properties as well as operational conditions. The oxidation behavior and the conditions typically favoring auto-ignition of crude oils are of utmost importance for light oil air injection.

Theoretically, if the heat generated by the oxidation reactions can overcome the heat loss the surroundings, the formation will be brought up to the ignition temperature in certain period of time. Spontaneous ignition, being the simplest ignition method is favorable condition in success and economic air injection. However, because of the low initial temperature of the formation and the poor reactivity of the crude oil, the magnitude of time delay is often so great that spontaneous ignition is not economically attractive. Unfortunately, not any research about how to improve light oil spontaneous ignition in air injection were documented before.

Crude oil oxidation and combustion has studied by various investigators. The methods of investigation are widely different.

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