Avaliação da origem de hidrocarbonetos observados na região limítrofe entre as bacias de Almada e Jequitinhonha, BA

Abstract

The following study, presents the geologic characterization from the structural and stratigraphic point of view of the petroleum system, found out on top of the basement located in the boundaries region of the Almada and Jequitinhonha basins. Taking as an starting point the oil samples gathered during the field phase, the geochemical analysis (Isotopes and biomarkers) were done, allowing the identification of two oil families: The first family, with high portions of steranes C28, predominance of the C23 tricycle and high portions of C29 hopane, which characterized a carbonate marine environment to source rock and most probably Albian to Turonian age. The second family, with δ13C -26.8 , and the imminent presence of gammacerane, which suggest a source rock generated in a hypersaline environment, commonly found in the Aptian. The interpretation done with the seismic lines facilitated the definition of a source rock migration system to reach the surface. The structural framework suggests a migrating process associated to the rift faults going to higher structures throughout a fault system NW-SE, found out in the region associated to the Ilhéus transference zones; the absence of an effective seal permitted the oil migration till reach the surface. The integral interpretations with the geochemical characterization of the oil indicate the presence of active petroleum system which suggests structural controls in the oil seeps. Furthermore, the current study addresses the faciologic, palynological and geochemical characterization (%TOC, IR, %S, isotopes and biomarkers) of sedimentary rocks cropping out in the Rio Doce formation between Ilhéus and Una cities. As from the correlation of the section study it is observed that these are represented at the higher portion of the Rio Doce formation, deposited in Miocene, also supported by the palynologic analysis. The deposition occurred inside a progressive trend of shallow upgrade, in the context of a highstand systems tract, where thick packages of argillaceous shale, intercalated with sand bars in an estuarine context