The properties of faults in the Brazil pre-salt: A reservoir characterization perspective

Fernández-Ibáñez, Fermín; Nolting, Andrea; Charles, Breithaupt; Brian, Darby; Jordan, Mimoun; Saturnina, Henares

doi:10.1016/j.marpetgeo.2022.105955

Cited by 12 publications

(1 citation statement)

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“…The process of hydrothermal silicification of carbonates plays an important role in modifying the original petrophysical properties of the rock. Although this effect on porosity is still debated, recent studies on Brazilian presalt hydrocarbon reservoirs (Fernández-Ibáñez, Nolting, et al, 2022) revealed an increase in porosity up to around 10% thanks to the hypogene dissolution of mineral grains and the brittle behaviour of silica. The localization of fractures in the stiff chert nodules has been observed also in Calixto (Pisani et al, 2022) and contributed to significantly increased porosity and Around 600 Ma, the basin was involved in the Brasiliano orogeny, and the depositional environment changed from an intracratonic gulf-like basin to a foreland basin (Santana et al, 2021).…”

Section: Formation and Speleogenetic Implicationsmentioning

confidence: 99%

Hydrothermal silicification and hypogene dissolution of an exhumed Neoproterozoic carbonate sequence in Brazil: Insights from fluid inclusion microthermometry and silicon‐oxygen isotopes

et al. 2023

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Hypogene dissolution‐precipitation processes strongly affect the petrophysical properties of carbonate rocks and fluid migration pathways in sedimentary basins. In many deep carbonate reservoirs, hypogene cavernous voids are often associated with silicified horizons. The diagenesis of silica in carbonate sequences is still a poorly‐investigated research topic. Studies exploring the complexity of silica dissolution‐precipitation patterns in hypogene cave analogues are therefore fundamental to unravel the diagenetic and speleogenetic processes that may affect this kind of reservoir. In this work, we investigated an exhumed and silicified Neoproterozoic carbonate sequence in Brazil hosting a 1.4 km‐long cave. Quartz mineralization and silicified textures were analyzed with a multidisciplinary approach combining petrography, fluid inclusion microthermometry, silicon‐oxygen stable isotope analyses and U‐Th‐Pb dating of monazite crystals. We found that an early silicification event caused the replacement of the dolostone layers with micro‐crystalline quartz forming chert nodules. This event was likely associated with mixing fluids (ancient Neoproterozoic seawater and hydrothermal solutions sourced from the underlying Mesoproterozoic basement) at relatively low temperatures (ca. 50–100°C) and shallow depth. After the tectonic deformation produced by the Brasiliano orogeny, silica dissolution was promoted by high temperature and alkaline hydrothermal solutions rising from the quartzite basement along deep‐rooted structures. Hypogene hydrothermal alteration promoted the dissolution of the cherty layers and the precipitation of chalcedony and megaquartz. Homogenization temperatures from primary fluid inclusions in megaquartz cement indicate minimum formation temperatures of 165–210°C. Similar temperature estimates (110–200°C) were obtained from the δ30Si and δ18O isotope systematics of quartz precipitated from hydrothermal solutions. The dissolved salts in the fluid inclusions were evaluated as NaCl + CaCl2 from microthermometric data combined with cryogenic Raman spectroscopy, corresponding to salinity ranging between 17 and 25 wt.%. No reliable age constraints for hydrothermal silica dissolution‐precipitation phases were obtained from monazite U‐Th‐Pb dating. However, our results, interpreted in the regional context of the São Francisco Craton, suggest that the Cambrian tectono‐thermal events could have been amongst the possible drivers for this hypogene process in the basin.

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Section: Formation and Speleogenetic Implicationsmentioning

confidence: 99%