Avaliação do potencial gerador de hidrocarbonetos na secção JOG16N-5 da formação K4 - Bacia de Maniamba

Abstract

The study of hydrocarbon source rocks constitutes essential information for assessing the risks involved in oil exploration, particularly in basins that have not yet been explored, such as the Maniamba Basin. Thus, there is a need to conduct research to expand knowledge of the hydrocarbons present in the karoo of the Metangula graben. This scientific project aims to study the organic content present in 20 samples from the JOG16N-5 drill core (12o33’36.62’’S and 34o 58’46.45’’E), belonging to the K4 formation, Maniamba Basin, located in the northwest of Niassa Province. For this purpose, samples were collected systematically and representatively, from fine-grained, dark-coloured clastic rocks and the rocks that were in the best preservation conditions (siltstones, siltstone sandstones and carbonaceous shales) between the intervals of 18.80 m and 58.88 m of the JOG16N-5 core, at a depth of 213 metres. The samples were processed following the standard non-oxidative palynological procedures described by Tyson and subsequently analysed on organopalynological slides using microscopic analysis (Visual analysis of kerogen). The visual analysis of kerogen was carried out on organopalynological slides under transmitted white light microscopy through the quantitative and qualitative examination of the components of the organic matter. The quantitative analysis consisted of the identification and counting of 300 organic components, which enabled the identification of the three main groups of kerogen: Phytoclasts, Palynomorphs and Amorphous Organic Matter. This analysis showed the predominance of the Phytoclast group, followed by the Palynomorph group and, to a lesser extent, Amorphous Organic Matter. Based on these results, three distinct palynofacies associations were identified, named palynofacies CD, C and D. The integration of palynofacies allowed the delineation of the depositional paleoenvironments along the analyzed section, indicating a fluvial-deltaic environment with a high sedimentation rate, under proximal oxic to very oxic depositional conditions, characterizing a vegetation that developed in a humid tropical climate. The qualitative analysis consisted of thermal maturation through the Spore Coloration Index (SCI) and Thermal Alteration Index (TAI), characterizing a degree of thermal maturation of immature, mature and supermature. Regarding the potential for generating hydrocarbons, three types of kerogen were classified, namely: type II characterizing a good potential for oil generation, type III with potential for generating dry and abundant gas, and type IV, characterized by highly oxidized organic matter and without potential for generating hydrocarbons. (TRADUÇAO NOSSA)