Integrated Geochemical Characterization of Brazilian Crude Oils by GC–MS, ESI(−) FT–ICR MS, Elemental Analysis, and Physicochemical Properties

An integrated analytical strategy combining gas chromatography coupled to mass spectrometry (GC–MS), negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry [ESI(−) FT–ICR MS], elemental analysis, and physicochemical characterization was applied to five Brazilian crude oils (A, C, D, E, and F) to investigate how information obtained from different analytical approaches can be integrated to understand their geochemical characteristics and properties. GC–MS analysis provided information related to source, maturity, depositional environment, and biodegradation. Oils A, C, D, and F showed TPP/Dia₂₇ and Tr₂₆/Tr₂₅ values > 1, indicating a predominantly lacustrine depositional environment, with a predominance of C₂₇ steranes (above 54%). Oils C, D, E, and F exhibited H32 22S/(22S+22R) values ranging from 0.59 to 0.62, within the thermodynamic equilibrium range for this parameter. For Oil E, terpene-based parameters such as H32 22S/(22S+22R) = 0.60, Ts/Tm = 0.40, and Ts/(Ts+Tm) = 0.29 indicated relatively high maturity, whereas the sterane indices St₂₉αααS/(S+R) = 0.36 and St₂₉αββ/(αββ+ααα) = 0.25 showed lower values, revealing non concordant responses among different biomarker families, possibly associated with secondary alteration processes. Oil E exhibited pronounced n-alkane depletion, although ratios based on more resistant biomarkers remained low (25NH/H30 = 0.06, 28,30-BNH/H30 = 0.07, and 25,30-BNH/H30 = 0.08), which may suggest severe alteration of the biomarker profile, including removal of the biodegradation indicators themselves. Complementarily, ESI(−) FT–ICR MS revealed differences in the composition of ionizable polar species, particularly within the O₂ class and its DBE distribution. Oil E contained 23.17% O₂ compounds and showed a low ratio between acyclic and cyclic species (A/C = 0.072), whereas Oils A and C exhibited more preserved profiles (A/C = 1.483 and 1.480, respectively), and D showed intermediate behavior (A/C = 0.703). These molecular differences were also reflected in macroscopic properties, with Oil E exhibiting the lowest API gravity (22.9), the highest total acid number (2.768 mg KOH g⁻¹), the highest O/C ratio (0.015), and the largest polar fraction (34.18%). In contrast, Oil D exhibited the highest API gravity (28.2), the highest H/C ratio (1.916), and the largest saturated fraction (48.23%), as well as the lowest dynamic viscosity (11.361) and polar content (20.21%), despite showing a profile considered intermediate by FT–ICR MS analysis (A/C between 0.2 and 1.2). This suggests the influence of different geochemical processes on the composition of this set of crude oil samples. Thus, integration of the analytical techniques provided complementary information, enabling a more comprehensive and consistent characterization of the geochemical processes responsible for the observed differences among the oils.