Abstract

The paper proposes an interpretation of the phenomena observed on several ARC (Accelerating Rate Calorimeter) tests performed with different crude oils. The ARC apparatus was used as a closed system and the gas formed at the end of the reactions were analyzed by chromatography. Low Temperature Oxidation (LTO) and Negative Temperature Coefficient (NTC) areas were identified during these tests. The proposed interpretation is based on an analogy with the reaction mechanisms occurring during light saturated hydrocarbon oxidation. The determination of kinetics parameters for oxidation reactions was investigated. In the meantime, limitations of the ARC device, when used as a closed system, clearly appeared. The conclusion is that not only the determination of basic kinetics parameters is generally not possible with ARC tests, but also that a serious selection of oil reservoir for air injection technique based on these tests seems questionable.

Introduction

Success of oil recovery by air injection greatly depends on knowledge of reaction mechanism between oxygen and oil in porous media. Oil oxidation during in-situ combustion involves numerous competing reactions occurring through different temperature ranges. Generally, in order to simplify the studies, investigators classify the reactions in three steps (Dubdub1 et al; Brigham2 et al).

- First, the low temperature oxidation (L TO) reactions, which are heterogeneous (gas/liquid) and generally produce polar compounds. For some light oils, if the reservoir conditions are convenient, L TO can produce mainly carbon oxides and water at long time (Solignac3).

- Then comes the medium temperature oxidation (MTO) : oxidation reactions are slow, therefore cracking/pyrolysis which leads to coke, becomes the main phenomenon.

- Finally, high temperature oxidation (HTO) : oxygen reacts with unoxidized oil, polar compounds and coke (Belgrave4 et al; Solignac3) to give carbon oxides and water.

This paper describes ARC experiments on crude oil oxidation and proposes an analysis of experimental data, using works (Ben-Ai'm5 et al; Le Chatelier6 et al; Newitt7 et al; Cathonnet8 et al) on light saturated hydrocarbons (CICIO). We compare heat rate behaviors measured by the calorimeter (Fig. 1) with zones of reactivity (cool and normal flames) occurring during oxidation of light saturated hydrocarbons in the gas phase.

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