High-permeability zones in folded and faulted silicified carbonate rocks – Implications for karstified carbonate reservoirs

Bruna, Vincenzo La; Bezerra, Francisco H.R.; Souza, Victor Hugo Proença; Maia, Rúbson Pinheiro; Auler, Augusto S.; Araújo, Raphael Ferreira de Souza Bezerra; Cazarin, Caroline Léssio; Rodrigues, Marcos Allyson Felipe; Vieira, Lucieth Cruz; Sousa, Maria O.L.

doi:10.1016/j.marpetgeo.2021.105046

Cited by 43 publications

(22 citation statements)

References 52 publications

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“…Some caves in the São Francisco Craton are also associated with silicification (Bertotti et al, 2020; La Bruna et al, 2021; Souza et al, 2021) or contain hydrothermal minerals, e.g. quartz and chalcedony filling veins and vugs (Cazarin et al, 2019).…”

Section: Geological Settingmentioning

confidence: 99%

“…An increasing number of publications have documented the development of hypogene caves and karst features in silicified carbonate rocks (Bertotti et al, 2020; La Bruna et al, 2021; Pisani et al, 2022; Sauro et al, 2014; Souza et al, 2021). Cavernous, sometimes mineralized solutional voids attributed to hydrothermal speleogenesis have been described in quartzites and skarns in Kyrgyzstan (Kornilov, 1978; Leven, 1961), USA (Colorado; Lovering et al, 1978) and Ukraine (Tsykin, 1989).…”

Section: Introductionmentioning

confidence: 99%

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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: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

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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“…The importance of faults to fluid flow is well documented through reservoir characterization and development (Caine et al 1996;Bense et al 2013;Vidal et al 2017;La Bruna et al 2021;Smeraglia et al 2021), and whilst faults can be observed using subsurface data analysis (e.g. seismic imaging) the fractures related to the faults commonly are not.…”

Section: B2 Influence Of the Kulmbach Faultmentioning

confidence: 99%

“…Faults and fractures are abundant discontinuity features in rocks that govern fluid flow in the subsurface (Caine et al 1996;Sibson, 1996;Curewitz & Karson, 1997;Connolly and Cosgrove 1999;Sanderson & Zhang, 2004;Kurz et al 2008;Zhang et al 2008;Bense et al 2013;Morley & Nixon, 2016;La Bruna et al 2021;Pisani et al 2022). These structural features develop at a variety of scales from large-scale regional faults to outcrop scale, fracture and stylolite networks, all of which can either enhance or impede flow in the subsurface (Caine et al 1996;Odling et al 1999;Bour et al 2002;Sanderson & Zhang, 2004;Manzocchi et al 2010;Bense et al 2013;Bruna et al 2019;Giuffrida et al 2019;Araújo et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Using fractured outcrops to calculate permeability tensors: implications for geothermal fluid flow and the influence of seismic-scale faults

et al. 2022

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Faulted and fractured systems form a critical component of fluid flow, especially within low-permeable reservoirs. Therefore, developing suitable methodologies for acquiring structural data and simulating flow through fractured media is vital to improve efficiency and reduce uncertainties in modelling the subsurface. Outcrop analogues provide excellent areas for the analysis and characterization of fractures within the reservoir rocks where subsurface data are limited. Variation in fracture arrangement, distribution and connectivity can be obtained from 2D fractured cliff sections and pavements. These sections can then be used for efficient discretization and homogenization techniques to obtain reliable predictions on permeability distributions in the geothermal reservoirs. Fracture network anisotropy in the Malm reservoir unit is assessed using detailed structural analysis and numerical homogenization of outcrop analogues from an open pit quarry within the Franconian Basin, Germany. Several events are recorded in the fracture networks from the Late Jurassic the Alpine Orogeny and are observed to be influenced by the Kulmbach Fault nearby with a reverse throw of 800 m. The fractured outcrops are digitized for fluid flow simulations and homogenization to determine the permeability tensors of the networks. The tensors show differences in fluid transport direction where fracture permeability is controlled by orientation compared to a constant value. As a result, it is observed that the orientation of the tensor is influenced by the Kulmbach Fault, and therefore faults within the reservoirs at depth should be considered as important controls on the fracture flow of the geothermal system.

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“…These reservoirs are mainly affected by diagenesis and post-deposition dissolution caused by karstification [1], which leads to highly fractured rocks contributing to the heterogeneity of the carbonate reservoirs [2]. The karstification process cause fragility and fracturing of the reservoir rocks changing the inherent properties of porosity and permeability, increasing the importance of the characterization of fracture (and overall discontinuities) in reservoirs to estimate fluid flow [3].…”

Section: Introductionmentioning

confidence: 99%

Adaptive Segmentation for Discontinuity Detection on Karstified Carbonate Outcrop Images From UAV-SfM Acquisition and Detection Bias Analysis

et al. 2022

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The identification of fracture and discontinuities has great importance on the fluid flow estimation in hydrocarbon reservoirs since they influence the properties of porosity and permeability. Due to the inaccessibility and sparsity of reservoir data, the fracture characterization is generally assessed through the study of outcrop analogues using remote sensing or in situ observations by a specialist. Considering the remote sensing methods, the unmanned Aerial Vehicle (UAV) acquisition combined with Structure from Motion (SfM) photogrammetry is a low-cost way to generate products like orthorectified images, allowing manual and automated methods of fracture trace detection. Automatic approaches, commonly used to address this problem, present some known limitations and disadvantages due to the nature of the outcrops and weather conditions during UAV acquisitions. In this work, we focus on fracture detection over karstic regions that are highly fractured. For this, we evaluated a series of adaptive segmentation methods based on thresholding. The Sauvola local adaptive segmentation presented the best result when compared to a manually annotated ground truth. The segmentation results were further improved by the use of the binary denoising method Non-Local means. We also carried an evaluation of the influence of the sun position in the fracture detection, and to reduce this inherent bias we combined three UAV acquisitions done over the karstic carbonate outcrop, namely Rosário pavement in the Jandaíra formation northeast Brazil. With the proposed methodology we acquired more accurate fracture data over the study area, which follows the directional statistics of previous works carried out in the region.

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High-permeability zones in folded and faulted silicified carbonate rocks – Implications for karstified carbonate reservoirs

Cited by 43 publications

References 52 publications

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

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

Using fractured outcrops to calculate permeability tensors: implications for geothermal fluid flow and the influence of seismic-scale faults

Adaptive Segmentation for Discontinuity Detection on Karstified Carbonate Outcrop Images From UAV-SfM Acquisition and Detection Bias Analysis

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