Low-temperature oxidation of light crude oil: Molecular composition and deposition characteristics of oxidation products

Air flooding is an important enhanced oil recovery technology for light crude oil development. Low temperature oxidation (LTO) occurs when air is injected into light crude oil, a large number of active substances are generated, which can enhance emulsification between crude oil and water. At the same time, the formation of the deposit may block high-permeability gas channels, improve sweep efficiency, and thereby further enhance oil recovery. In this study, LTO experiments were conducted on light crude oil to investigate the change of molecular composition associated to deposition. The oxidation degree increases significantly with the increase in temperature in LTO. Molecular-scale differentiation of nitrogen and oxygen compounds is characterized in relative abundance and double bond equivalent (DBE) versus carbon number distribution of compound classes using multi-mode ionization Orbitrap MS. Oxygenation and cracking reactions occur simultaneously, with their competitive interplay collectively determining the deposit architecture. The oxygenation reaction results in the emergence of more oxygen compounds containing multiple oxygen atoms in oxidized oil, which are absent in crude oil. The cracking reaction produces small molecular compounds with low carbon numbers and low DBE values, which are adsorbed onto the coke surface of the deposit. The reaction pathways of several typical nitrogen compounds and oxygen compounds are also inferred in this study. This work provides molecular level insights into the mechanisms of LTO in enhancing oil recovery.