Geração não convencional de hidocarbonetos na região carbonífera de Santa Catarina

Abstract

In the region of Lauro Müller, south of Santa Catarina, the presence of oil in sandstones of Rio Bonito and Palermo formations were observed in several wells and in the galleries of a coal mine. Samples of oil were subjected to stable carbon isotopes and gas chromatography mass spectrometry analysis to identify its origin. The oil had typical features of a hypersaline anoxic environment, achieving a positive correlation with Assistência Member of Irati Formation. Molecular parameters revealed that it was generated during the peak of hydrocarbon generation and is light to moderately biodegraded. The comparison between oil encountered in Lauro Müller and the tar sands of Anhembi (SP) revealed molecular differences related to organic facies, level of biodegradation and thermal maturity. The generation of oil in southern Santa Catarina is closely related to the thermal effect of igneous intrusions in the source rocks of Irati formation, given that the unit is thermally immature in most of the basin. The oil would have migrated laterally from Irati Formation to the reservoir sandstones of Rio Bonito Formation through faults with vertical slips over 150 m, identified on maps and geological sections. Pyrolysis, stable carbons isotopes and biomarkers analysis was also performed in a local section of Irati Formation to evaluate the heating effect of two dolerite sills intruded into Assistência Member. It was observed an increase in δ13C toward the intrusive contacts and that Assistência Member was completely overmature. The thermal halo below the lower sill reached, at least, the bottom of the Irati Formation, located at a distance of 1.4 times the thickness of the intrusive body. Samples from the lower portion of Palermo Formation, collected in the well CAT 204, and the three main coal layers from southern Santa Catarina, collected in Carbonífera Catarinense s mines, are also thermally mature, suggesting the proximity of other intrusive bodies. Thus, it is concluded that there was a general heating of the sediments of southern Santa Catarina caused by the high incidence of igneous intrusions in the region.