Geoquímica orgânica aplicada à formação Irati, área de Herval, Rio Grande do Sul (RS), bacia do Paraná

Abstract

The current research had the main focus on the geochemical study of a borehole in the Parana Basin at Herval city (RS), aiming to fill some gaps in the organic geochemistry of the Irati Formation. Ten chemical-stratigraphic units were defined from analytical data of Total Organic Carbon (TOC), total sulfur, insoluble residue, gamma-rays, isotopes of organic carbon, Rock-Eval pyrolysis and biomarkers. Distributions the depositional environment, source of organic matter and the lithological influence were characterized by the relative abundance of biomarkers. The depositional environments of the units A, B, C were characterized as normal saline oxic. The top of unit B represents the maximum flooding surface with increased TOC values. Based on the biomarkers it was possible to characterize a depositional paleoenvironment with some anoxic tendency. Shales and carbonate intercalations occur in the units D and G . In these units, the TOC concentration is above 1%, but only in the G unit there is good potential to produce gas and condensate. The E and I units present high contents of total organic carbon close to 16%. The pyrolysis "Rock-Eval" data indicate a good to excellent potential for generating oil and gas. The isotopic data allowed division of the Irati Formation in three cycles. The first, from bottom to top, corresponds to the Taquaral Member, the other two cycles correspond to the Assistência Member. In the Assistência Member δ13C range varies according to salinity, primary productivity increases and the organic matter preservation (anoxic depositional environment).