Function of aromatic compounds as indicators in laboratory experiments of heavy oil with fire flooding

Identifying whether high-temperature oxidation is realized in fire flooding has become one of the technical difficulties in evaluating the effect of fire flooding for heavy oil reservoirs. In order to study how the chemical properties of crude oil varied during fire flooding, a series of heavy oil fire flooding laboratory experiments were carried out using a three-dimensional physical model, and the gas chromatography-mass spectrometry of aromatics were performed for the crude oil before and after high-temperature oxidation during fire flooding. Results show that after fire flooding, the relative contents of naphthalenes, phenanthrenes and polycyclic aromatic hydrocarbons in the crude oil sample increased, while the relative content of tri-aromatic steroids decreased. During fire flooding, naphthalenes and phenanthrenes were all prone to demethylation, methyl migration and methyl substitution, showing significantly higher thermal stabilities in β-naphthalenes and β-phenanthrenes relative to α-naphthalenes and α-phenanthrenes. Due to the difference in thermal stability between 4-methyldibenzothiophene and 1-methyldibenzothiophene, the high-temperature oxidation in fire flooding could be identified according to the changes in their relative contents and the distribution characteristics of their spectra. Anthracene in polycyclic aromatic hydrocarbons could be used as a marker of high-temperature oxidation in fire flooding, while the changes in perylene/benzo(e)pyrene, fluoranthene/pyrene and anthracene/phenanthrene ratios were also good indicators for high-temperature oxidation in fire flooding. As observed from these findings, it can thus be concluded that the variation characteristics and characteristic markers of aromatic compounds in crude oil are good indicators for combustion state during fire flooding, providing favorable support for the identification of combustion state in heavy oil fire flooding.