DISTINGUISHING PRE-SALT OIL FAMILIES IN THE SANTOS BASIN USING CHEMOMETRIC ANALYSIS OF A LARGE DATABASE

Petroleum biomarkers are complex organic used to unravel the origin and maturity of petroleum (source rock facies, age, type of organic matter, and maturity) as well as secondary processes (e.g. biodegradation and evaporative fractionation). In large hydrocarbon accumulations, such as those in the pre-salt of the Santos Basin, it is challenging to interpret a large dataset using only bivariable and/or ternary diagrams. In this context, to improve the interpretation of the pre-salt petroleum system for the Santos Basin, we employed multivariate statistical analysis to distinguish oil families, particularly those associated with the main source rock referred to as the “Jiquiá Principal”. Eight hundred petroleum samples from Santos Basin were analyzed, including Itapu, Cernambi, Berbigão, Búzios, Mero, Libra Central, Atapu, Sururu, Lula and Júpiter fields. Source related biomarker ratios were determined using the GC-MS method, in keeping with standard geochemical procedures. Further, a statistical analysis was performed to identify the most representative ratios for characterizing the source of organic matter, narrowing the analysis to eight main ratios (60% of the data variance; PC1 and PC2). Regarding the source-related parameters and the principal component analysis, five groups were observed which were directly related to different kitchens. The accumulations associated with the main depocenter, however, show a certain distinction between the samples from the different petroleum fields, making it possible to refine and subdivide the families into three sub-groups. These compositional distinctions are interpreted to reflect differences in migration routes which were independently tested and confirmed by numerical simulations of petroleum system as well as geochemical evidence for mixture of oils from distinct kitchens, Tupi and Sapinhoá samples. Oil samples from the Cernambi and west Tupi are sourced from the Ilha grande and Tupi Oeste Kitchens. Oils from the Júpiter field are interpreted to be sourced mainly from an external kitchen. Samples located farther from the main family regions represent smaller local kitchens, such as some samples from the Sapinhoá accumulation, which exhibit compositional differences indicative of more siliciclastic organic facies. It should be emphasized that all accumulations characterized as local are below the oil-water contact. Overall, the analysis of this dataset provides an opportunity to evaluate previously proposed models, developed using fewer samples, to explain compositional variations within the pre-salt petroleum system. This broader dataset reveals a wider range of fluctuations in diagnostic biomarker ratios, which is crucial for enhancing our understanding of the region. Moreover, our findings hold significant implications for oil-oil correlation in the context of oil spill investigations, offering a preliminary approach to identify the potential correlation between spilled oils and pre-salt samples.