High resolution molecular organic geochemistry assessment of Brazilian lacustrine crude oils

As most of the oils in the Recôncavo Basin are genetically related and have experienced nearly equivalent thermal stress, it is difficult to differentiate them using standard techniques. However, differentiation can be accomplished using new analytical techniques, including comprehensive two-dimensional gas chromatography (GC×GC)-time of flight mass spectrometry (TOFMS). In this investigation, GC×GC-TOFMS was applied for the characterization of 20 selected Recôncavo Basin crude oils from a wide geographical distribution. Source and maturation parameters were determined based on the analysis of saturated hydrocarbons, aromatic compounds and diamondoids using GC×GC-TOFMS. Chemometric techniques were applied in order to expand the overall understanding of the sample characteristics. It was found that β-carotane and gammacerane were highly important for differentiating oils from the central portion of the basin, while two southern oils were differentiated by their sulfur-containing aromatic compounds. Diamondoid analysis was fundamental to evaluating maturity. The results of this study show how previously overlooked, minor oil components are important for differentiating genetic groups, compounds that were neglected prior to the application of GC×GC-TOFMS.