Fingerprinting cromatográfico de hidrocarbonetos alifáticos em amostras de óleo do pré-sal brasileiro por CG-DIC

Abstract

Considered one of the most important discoveries of the last decades, the pre-salt corresponds to an area of oil and natural gas reservoirs located below a layer of salt that extends from the coast of the State of Espírito Santo to the coast of the State of Santa Catarina. Petroleum is a highly complex analytical matrix that is composed of several classes of hydrocarbons and non-hydrocarbons in solid, liquid and gaseous states. Through appropriate analytical methodologies, it is possible to characterize its “molecular signature” and evaluate its molecular markers. The main objective of this work is to characterize the chromatographic fingerprinting of aliphatic hydrocarbons (n-alkanes and isoprenoids) in three samples Brazilian pre-salt oil. Aliphatic hydrocarbons were obtained by the extraction step and by the cleanup step and were identified and quantified by gas chromatography with flame ionization detector (GC-FID). The n-alkanes were detected in the series from n-C9 to n-C31, in addition to the isoprenoids pristane and phytane, and the sum of the concentrations and the individual concentrations varied from 4177.34 - 5053.38 μg‧g-1 and 24.47 - 541.58 μg‧g-1, respectively. The Brazilian pre-salt oil samples presented a similar chromatographic profile, with unimodal distribution of n-alkanes, with maximum abundance between n-C14 and n-C17 and with a decrease of n-alkanes after n-C21. Furthermore, it was possible to visualize a small elevation of the baseline in the chromatograms, which may indicate the presence of the unresolved complex mixture (UCM). For the evaluation of molecular markers, the diagnostic ratios CPI, TAR, Pr/n-C17, Ph/n-C18, Pr/Ph and Res/UCM (%) were used. The results suggested that the oil samples are of marine origin and from an oxide depositional environment and present a high level of maturation and low extent of biodegradation.