Feldspar Albitization With Implications for Reservoir Quality Evolution of Eocene Turbidite Sandstones in Offshore Espírito Santo Basin, Eastern Brazil

ABSTRACT

The diagenetic albitization of plagioclase and K‐feldspar grains is a transformative process that significantly alters sandstone's detrital composition and formation water chemistry, impacting reservoir quality. In this study, Eocene turbidite sandstones from the offshore Espírito Santo Basin, Brazil, were investigated to elucidate the role of albitization in porosity and permeability. Petrographic, geochemical, and petrophysical analyses revealed that feldspar albitization contributed to reservoir quality by creating intragranular porosity. The degree of albitization is influenced by feldspar composition. Orthoclase is more extensively albitized than microcline. Calcic plagioclase with 40–60 mol% anorthite is more albitized than sodic plagioclase (20–40 mol% An) derived from amphibolitic metamorphic rocks. Albitization was more pronounced in distal turbidite sandstones, owing to their deeper burial history. The process occurred within a temperature range of approximately 60–100°C, as inferred from paragenetic sequences and isotopic data. Although intragranular porosity associated with albitization exhibits a moderate positive correlation with porosity, its impact on permeability remains negligible. These findings advance the understanding of diagenetic albitization and its implications for reservoir quality in albitized clastic systems, offering insights into the controls and conditions of albitization and its broader significance in hydrocarbon exploration.