Molecular-level characterization of Brazilian pre-salt crude oils by advanced analytical techniques

Abstract

The increase in offshore oil production in Brazil, especially from the pre-salt layer, has resulted in the need for faster and more reliable techniques for the chemical characterization of these oils. This study consisted of characterizing the substances present in Brazilian pre-salt oils and semi-quantitatively evaluating them using complementary high-resolution analytical techniques such as high-temperature comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (HT-GC × GC-TOFMS) and a flame ionization detector (HT-GC × GC-FID) and Orbitrap high-resolution mass spectrometry (Orbitrap-HRMS) with electrospray ionization [ESI(±)]. Three pre-salt oils from the Santos and Campos Basins were evaluated. HT-GC × GC-FID was used to quantify the n-paraffins (47.1–57.7 μg mg−1), iso-paraffins (24.9–42.4 μg mg−1), and naphthenics (45.6–70.3 μg mg−1). Both SAN-34D and CAM-48 oils were classified as paraffinic, while SAN-07 was classified as paraffinic-naphthenic. The N class was the majority for the three crude oils in both ionization modes, and the main compounds identified were carbazoles, benzocarbazoles, and dibenzocarbazoles. Phenolic compounds were also detected, and the O2 class was observed as having higher percentage intensities of double bond equivalent (DBE) 1, which was assigned as a carboxylic acid. This is the first work to present a comprehensive report on the chemical characterization of Brazilian pre-salt oils. The results show that the combination of advanced techniques offers a powerful tool for a wide-ranging characterization of saturated, naphthenic, and aromatic hydrocarbons in addition to mid-polar to polar compounds in the pre-salt oils. This data could have an important impact on field development decisions and on the economic value of crude oils.