Análise de palinofácies na avaliação do potencial gerador da Formação Pojuca, Bacia do Recôncavo

Abstract

PALYNOFACIES ANALYSIS IN EVALUATION OF HYDROCARBON POTENTIAL GENERATOR OF THE POJUCA FORMATION, RECÔNCAVO BASIN. This paper deals with the study of source rock potential and its depositional environment. These strata belong to Pojuca Formation and occur in syn-rift sequence of the Early Cretaceous age (Hauterivian-Barremian) in the region of Aramari, a little-explored area of the northwestern Recôncavo Basin. The potential generator of these sediments was evaluated based on studies of palynofacies, Total Organic Carbon (TOC) analysis and Rock-Eval pyrolysis. For the evaluation of the maturation thermal of organic matter of the sediments was used the Spore Coloration Index (SCI); and the palynological study was used to identify the paleoenvironment of these strata. By integration of data from "Rock-Eval" pyrolysis and palynofacies it was possible to identify the prevalence of type II and III kerogen, with varying degrees of quality, allowing for individualization of three palynofacies. The material has predominance of amorphous organic matter of lacustrine origin, with TOC data ranging from 0.95% to 4.71%. The organic matter is a great potential hydrocarbon generator, indicated by S2 values that reach 26.33 mgHC/g rock. SCI values between 4.5-5.0 corresponding to 0.5 reflective of vitrinite (% Ro) demonstrated that the studied section is entering the maturation window. With the data acquired through palynofacies analysis and palynological associations, it can be inferred that a continental deposition environment (deltaiclake) characterizes the sedimentation of the Pojuca Formation with the presence of higrophytic and xerophytic elements, indicating that the vegetation developed in an arid and dry paleoclimate with wet niches locally and latitude next to the present. The data show that the studied area is placed in anoxic conditions containing good quality kerogen and suitable for the generation of hydrocarbons.

Geoquímica Orgânica de Folhelhos da Formação Pojuca, Bacia do Recôncavo, Brasil

“…Folhelhos pretos enriquecidos em carbono orgânico ocupariam uma posição específica neste ciclo, segundo o autor, estando relacionados ao estágio inicial em que se reduz o influxo de água e, consequentemente, o aporte de terrígenos, para implantação de um regime climático com balanço hídrico negativo (aridização), com redução do nível de base. Portela et al (2016) também verificaram uma ciclicidade, na qual se alternam depósitos de sistemas lacustres transgressivos e regressivos devido a ocorrência de flutuações periódicas da lâmina d'água como resultado de variações climáticas com reflexos nas proporções das palinofácies analisadas. Guzzo (1997), verificou deflexões nos valores da razão isotópica δ 13 C e δ 18 O de carbonatos presentes em folhelhos da Formação Pojuca.…”

“…A princípio, esta deposição se deu em lago restrito e posteriormente, pela intensa atividade tectônica, esse lago foi ampliado durante a deposição da Formação Maracangalha. A diminuição contínua da taxa de subsidência possibilitou que deltas progradassem por meio das plataformas existentes, ocupando os depocentros com arenitos deltaicos das Formações Marfim e Pojuca (Magnavita, 1992;Portela et al 2016).…”

Modelagem numérica conjunta de processos termomecânicos e superficiais na evolução pós-rifte das bacias do Recôncavo, Tucano e Jatobá

“…Furthermore, during the Late Hauterivian the Taquipe Canyon was formed in a portion of the Recôncavo basin, representing a site for preferential lacustrine deposition (Taquipe Formation) amid the prevalence of deltaic sediments in the basin (Silva et al, 2007). The analysis of palynofacies encountered in the Pojuca strata in the Recôncavo graben, together with pyrolysis data from samples collected at outcrops, indicate that rocks belonging to this formation may constitute prolific hydrocarbon sources (Portela et al, 2016;Miranda et al, 2021).…”

“…Later on, subdued tectonic activity made it possible for the deltaic system to expand to the southern portion of the rift, as indicated by the occurrence of Early Hauterivian deltaic sandstones belonging to the Marfim Formation in the Recôncavo basin, as well as deltaiclacustrine cycles ascribed to the Pojuca Formation, which are related to an alternance between transgressive and regressive lacustrine systems in the rift (Silva et al, 2007;Costa et al, 2007b;Portela et al, 2016). Furthermore, during the Late Hauterivian the Taquipe Canyon was formed in a portion of the Recôncavo basin, representing a site for preferential lacustrine deposition (Taquipe Formation) amid the prevalence of deltaic sediments in the basin (Silva et al, 2007).…”