Roles of alkanes, alcohols, and aldehydes for crude oil oxidation during the air injection process

Abstract

Although the air injection process (AIP) has been applied for enhanced oil recovery purposes for many decades now, the oxidation mechanism behind the exotherm has not yet been widely discussed. Previous methane oxidation studies have stated that hydrocarbon oxidation is a chain reaction. Four types of hydrocarbons have been proposed to significantly affect the hydrocarbon oxidation, namely, alkanes, alkyl peroxides, alcohols, and aldehydes. Therefore, the functional groups of hydrocarbons might be the key to understanding the oxidation behaviors of crude oil during the AIP.This study used an accelerated-rate calorimeter to investigate the self-heating behaviors of three types of hydrocarbons and their corresponding mixtures with crude oil under high pressure. n-Decane, 1-decanol, and 1-decanal were selected for use herein because of their availability to represent the self-heating behaviors of the hydrocarbon types. The oxidation behaviors of hydrocarbons with a longer hydrocarbon chain can be explained by analogy with the results of previous methane oxidation studies; thus, the enthalpy from the low-temperature oxidation mainly comes from the oxidation process from alkanes to alcohols. The negative temperature coefficient region is mainly caused by the reactions that turn alcohols into aldehydes. Aldehydes are the direct fuel for high-temperature oxidation and have the lowest activation energy among the three tested types of hydrocarbons. More aldehydes in the crude oil should be favorable for the AIPs in low-temperature reservoirs.