Arcabouço estratigráfico e possíveis horizontes geradores de hidrocarbonetos em uma seção devoniana da borda sudoeste da Bacia do Parnaíba

Abstract

The Parnaíba Basin is located, partially, in three regions of the Brazilian territory - North, Northeast and Center-West - which it includes portions of the following states: Ceará, Piauí, Maranhão, Pará and Tocantins, encompassing an area about 600,000 km2. The stratigraphic units that cover the Basin are arranged in three major cycles, namely: the continental-marine-continental sequence of neo-ordovician to eocarboniferous age; the second, terrigenous sediments deposited at Neocarboniferous to Jurassic; and the third the rift phase of late cretaceous. The material of this study covered two wells in continuous cores: GASBRAS-1-RS-TO and GASBRAS-2-RS-TO, these wells enclose the Itaim and Pimenteiras Formations, and, partially, the top of the Jaicós Formation. The Itaim Formation is comprised of fine to medium sandstones, rarely coarse, and locally shales. The Pimenteiras Formation, on the other hand, consists, predominantly, of dark grey to black shales, which may occur interspersed with siltstone and sandstone layers. At cores studies, it was possible to carry out faciological analysis, determination of depositional paleoenvironments, chemostratigraphic characterization at the Itaim Formation, in well 2, supported by data from geochemical analyzes (Total Organic Carbon and Pyrolysis), as well as description of those within the Pimenteiras Formation of the radioactive shales, known as: A, B and C. The last Formation has potentially hydrocarbon generating intervals arising from maximum flooding surfaces in the Devonian. These intervals are of interest for exploration, since from the mentioned shales, B and C, reached , respectively, about 17 m and 38 m in thick, with an average TOC of 2.3% and 2.4%. The shale A is the level with the lowest average TOC content (0.68%), thus it is suggesting, that the first two levels mentioned above it has favorability for to generation of hydrocarbons.