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SIGNIFICANCE OF ACIDIC POLAR SPECIES ASSESSED BY FT-ICR MS TO REVEAL GEOCHEMICAL INFORMATION OF OILS FROM THE SERGIPE-ALAGOAS BASIN

Summary In this work, we investigate in detail the acidic polar composition of five oil samples from distinct fields of the Sergipe-Alagoas Basin (Brazil) by FT-ICR MS using ESI(-). We aim to present the significance of acidic species to reveal geochemical information of petroleum fluids and to reconstruct the maturity and depositional environment of the source rocks by extracting features of biodegradation. The heteroatom class distribution of the oil samples shows great variability, with a higher abundance of N and O2 classes, followed by the O1, NO, and NO2 classes. The biodegradation was successfully assessed by the A/C ratio and SA index based on the O2 compounds, classifying the samples in four levels of biodegradation (from non to heavy biodegraded). The maturation was assessed by the distribution of the N compounds, showing that samples have reached the peak of the oil window, but the heavy biodegraded oil was misleading evaluated with higher maturity. The depositional environment was evaluated using the C27/C28 (DBE 4) ratio and the suggested Isoprenoidyl phenol index, differentiating the lacustrine oil samples from the marine evaporitic ones. However, care should be taken in the assessment of highly biodegraded oils since the acidic compounds are considerably affected.