oa Untargeted GC×GC-Tofms Analysis to Distinguish Pre-Salt Crude Oils from a Field in Santos Basin: Insights from Light Hydrocarbons

Crude oil analysis based on comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) allows detailed light hydrocarbon (LH) fingerprinting. An untargeted GC×GC-TOFMS pixel-based approach followed by chemometrics analysis was performed to distinguish 47 pre-salt crude oils collected from a field in the Brazilian Santos Basin. The unsupervised Principal Component Analysis (PCA) showed the presence of 3 outliers influenced by the positive loadings of the PC1. Methylcyclohexane and C7-C11 n-alkanes are the LHs that contribute most to the differences in sample discrimination for this specific sample set. Additionally, cyclohexane, trans-1,2-dimethylcyclopentane, C7-C9 alkylcyclohexanes, C7-C11 methyl and dimethyl iso-alkanes, and alkylbenzenes also contributed to this differentiation. The enrichment in LHs for the outliers would be due to in-reservoir secondary alteration processes, as geochemical data indicate the same source rocks for all samples. The untargeted GC×GC-TOFMS molecular approach revealed subtle differences in the LH compositions of pre-salt crude oils despite their high level of similarity, allowing an in-depth detailed assessment of sample-distinguishing analytes that are relevant to the model and may reflect physicochemical processes in the oil field. The LH molecular approach, when applied in an integrated way, may contribute to understanding possible in-reservoir alteration processes that can affect light hydrocarbon composition.