Primary composition and diagenetic patterns of sandstones from Barra de Itiúba Formation in Atalaia High, Sergipe Sub-Basin

Abstract

ABSTRACT:The petrologic analyses of 40 thin sections from two wells located in Atalaia High, offshore of Sergipe Sub-Basin, allowed the identification of primary composition and diagenetic patterns of Barra de Itiúba Formation. The original detrital compositions included arkoses, sublithic, and lithic sandstones. The main diagenetic processes observed were: compaction of metamorphic rock fragments and mud intraclasts, generating pseudomatrix; precipitation of quartz and feldspar overgrowths and outgrowths, cementation and grain replacement by kaolinite; dolomite and ferrous dolomite/ankerite; pyrite; iron oxides and hydroxides; and diagenetic titanium minerals, in addition to dissolution phases during eo-, meso-and telogenesis. The macroporosity in the two studied wells is primary intergranular, but there is secondary porosity due to dissolution of primary and diagenetic constituents, as well as fracture porosity. Thirteen reservoir petrofacies were defined and grouped into four reservoir petrofacies associations. They reflect the reservoir quality in microscale: good, medium and low-quality and non-reservoir. The good-quality is characterized by average total porosity greater than 15%, whereas the medium shows average total porosity greater than 7%. Lowquality presents average total porosity between 1 and 4%, and the non-reservoir has an average total porosity consistently less than 1%. Overall, the studied reservoirs consist on low-quality and non-reservoir rocks, which are intercalated with levels of mediumand good-quality. The loss of original porosity was mainly due to mechanical compaction (generating pseudomatrix), and cementation by kaolinite and dolomite. Preservation of primary porosity was favored by the presence of quartz overgrowths. KEYWORDS:Reservoir Quality; Sergipe-Alagoas; Cretaceous; Diagenesis; Petrography. RESUMO: As análises petrológicas de 40 lâminas em dois poços localizados no Alto de Atalaia, offshore da Sub-Bacia de Sergipe, permitiu a identificação das composições primárias e dos padrões diagenéticos para a Formação Barra de Itiúba. As composições detríticas originais das rochas são subarcósios, sublitarenitos e litarenitos. Os principais processos diagenéticos observados foram: compactação dos fragmentos de rocha metamórfica e intraclastos lamosos

Influência Dos Processos Diagenéticos Na Porosidade Dos Arenitos Da Formação Iborepi, Bacia De Lavras Da Mangabeira, Estado Do Ceará

“…A composição detrítica dos arenitos estudados também influenciou a redução da sua porosidade (Rodrigues & Goldberg, 2014), pois arenitos com grãos micáceos têm maior redução de porosidade devido à compactação mecânica. Além disso, muitos _________________________________________________________________________________________________ são substituídos por caulinita, obliterando a porosidade (RODRIGUES & GOLDBERG, 2014).…”

Petrography, Diagenesis and Considerations About Provenance of the Itapecuru Formation in Northern Maranhão (Lower Cretaceous, Parnaíba Basin, NE Brazil)

“…Bocardi et al, 2006, como em bacias marginais (e.g. Rodrigues & Goldberg, 2014), inclusive nas de Bragança-Viseu e São Luís (Schrank & De Ros, 2015), contíguas à Bacia do Parnaíba (Figura 1).…”