Excess permeability in the Brazil pre-Salt: Nonmatrix types, concepts, diagnostic indicators, and reservoir implications

Fernández-Ibáñez, Fermín; Jones, Gareth D.; Mimoun, Jordan G.; Bowen, Melanie G.; Simo, J.A.; Marcon, Virginia; Esch, William L.

doi:10.1306/10042120171

Cited by 20 publications

(6 citation statements)

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“…This also includes fabric selective (mouldic porosity) that has been dissolutionally enhanced/enlarged. These non‐matrix features are typically distributed randomly, where local mechanical and chemical processes play a role in their distribution (Fernandez‐Ibanez et al ., 2022). This classification follows that of Lucia (1995) for vuggy pore space.…”

Section: Field Data Analytical Methods and Core Descriptionsmentioning

confidence: 99%

Three‐dimensional stratigraphic architecture, secondary pore system development and the Middle Pleistocene transition, Sandy Point area, San Salvador Island, Bahamas

Nolting,

Kerans,

Fernandez‐Ibanez

et al. 2023

Sedimentology

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The Bahamian Archipelago has been the subject of extensive studies of stratigraphy, carbonate island morphology and diagenetic overprinting for many decades. A recently‐acquired dataset comprised of high‐resolution light detection and ranging, tightly spaced cored boreholes with image logs, thin sections, porosity and permeability measurements, and isotopic geochemical analyses provides a unique opportunity to perform detailed sequence stratigraphic analysis. This multi‐faceted study first establishes a new high‐resolution sequence stratigraphic framework for the Sandy Point area of San Salvador Island, encompassing six unconformity bound sequences (exposure surfaces) representing varying lengths of missing time. The stratigraphically lowest sequence is Late Pliocene in age and is dominated by reef facies capped by an extensive laminar caliche that represents 1.5 million years of exposure. The overlying Early Pleistocene is split into two sequences, EP1 and EP2, which are both dominated by low‐energy subtidal facies. The upper three sequences are tied to the Marine Isotope Stage 11, 9 and 5e interglacials, and are distinctly different in facies composition and architecture, being dominated by higher energy facies distributed in a more complex mosaic. The new stratigraphic framework highlights significant changes in depositional style and facies architecture that can be linked to increasing sea‐level amplitude oscillations and greater climate gradient at the Mid Pleistocene Transition. The well‐constrained framework is then used to provide key context for observed complex diagenetic evolution through repeated sea‐level inundation and subaerial exposure. These results suggest that well‐developed subaerial exposure surfaces drive increases in non‐matrix features in the subsequent stratigraphic package following exposure as the well‐cemented exposure surface acts to concentrate fluid flow and dissolution. Integration of non‐matrix features within this framework highlights the importance of dissolution/cementation patterns on formation of these modified unconformity surfaces for focusing later meteoric diagenesis and creating enhanced fluid flow pathways for continued multicyclic diagenetic events.

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Section: Field Data Analytical Methods and Core Descriptionsmentioning

confidence: 99%

Three‐dimensional stratigraphic architecture, secondary pore system development and the Middle Pleistocene transition, Sandy Point area, San Salvador Island, Bahamas

Nolting,

Kerans,

Fernandez‐Ibanez

et al. 2023

Sedimentology

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“…This section delves into the nuanced responses of data inputs within porous environments, particularly focusing on carbonate reservoirs renowned for their intricate porosity systems. These systems are categorized into porosity stemming from the matrix (interparticle porosity) and nonmatrix-related porosity, encompassing features like caves, fractures, and vugs ( [66]). The sonic log emerges as a key informant, furnishing insights into interval transit time and establishing a direct linkage with interparticle porosity.…”

Section: Responses Of the Data Inputs Against Porous Environmentmentioning

confidence: 99%

“…This filtrate, distinguished by lower density and prolonged travel time compared to the host rock, becomes a crucial indicator. Intervals exhibiting low density values and prolonged travel time, contrasted with the established background values for carbonates, are interpreted as zones with a heightened percentage of pore spaces ( [20,21,66]).…”

Section: Responses Of the Data Inputs Against Porous Environmentmentioning

confidence: 99%

Geological Insights from Porosity Analysis for Sustainable Development of Santos Basin’s Pre-Salt Carbonate Reservoir

Vásconez Garcia,

Mohammadizadeh,

Avansi

et al. 2024

Preprint

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Carbonate reservoirs, influenced by depositional and diagenetic processes and characterized by features like faults and vugs that impact storage capacity, require more than traditional Borehole Imaging logs (BHI) for accurate porosity data. This data is essential for geological assessments, production forecasting, and reservoir simulations. This work aims to address this limitation by developing methods to measure and monitor the sustainability of carbonate reservoirs and exploring the application of sustainability principles to their management. The study integrates BHI and conventional logs from two wells to classify porosity-based facies within the Barra Velha Formation (BVF) in the Santos Basin. The methodology involves four steps: (i) analyzing conventional logs; (ii) segmenting BHI logs; (iii) integrating conventional and segmented BHI logs using Self-Organizing Maps (SOM); and (iv) interpreting the resulting classes. Matrix porosity values and non-matrix pore sizes categorize the porosity into four facies (A to D). Facies A has high non-matrix porosity with 14,560 small megapores, 5,419 large megapores, and 271 gigapores (71.9%, 26.76%, and 1.34% of the 20,250 pores, respectively). Facies B shows moderate non-matrix porosity with 8,669 small megapores, 2,642 large megapores, and 33 gigapores (76.42%, 23.29%, and 0.29% of the 11,344 pores, respectively) and medium matrix porosity. Facies C exhibits low non-matrix porosity with 7,749 small megapores, 2,132 large megapores, and 20 gigapores (78.27%, 21.53%, and 0.20% of the 9,901 pores, respectively) and medium matrix porosity. Facies D has low non-matrix porosity with 9,355 small megapores, 2,346 large megapores, and 19 gigapores (79.82%, 20.02%, and 0.16% of the 11,720 pores, respectively) and low matrix porosity. The novelty of this work lies in integrating data from two sources to classify porosity across the Pre-Salt reservoir interval, serving as a proxy for preliminary litho-facies identification without core data. This study advances our understanding of carbonate reservoir sustainability and heterogeneity, offering valuable insights for robust, sustainable reservoir characterization and management in the context of global environmental and geological changes.

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“…Karst features in deep reservoirs are commonly attributed to hypogene dissolution (hypogene speleogenesis) resulting from upwelling and migration of thermal groundwaters (Andreychouk et al, 2009;Dublyansky, 1990;Klimchouk, 2007Klimchouk, , 2019. Hydrothermal alteration in carbonate reservoirs resulting in cavernous vugs and nonmatrix permeability is a common phenomenon, especially along fault and fracture zones (Álvaro, 2013;Fernández-Ibáñez, Jones, et al, 2022;Strugale & Cartwright, 2022;Zhou et al, 2014). These hypogene karst processes generate non-fabric-selective interconnected pore systems, resulting in heterogeneous porosity and highly anisotropic rock permeability (Fernández-Ibáñez, Jones, et al, 2022;Trice, 2005), which has implications not only for hydrocarbon exploration but also for the characterization of geothermal resources and groundwater reserves (Audra et al, 2022;Goldscheider et al, 2010;Montanari et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Solutional voids and karstic vugs are commonly found in quartzites and silicified (cherty) carbonates in many hydrocarbon reservoirs in sedimentary basins, such as North Slope in Alaska (e.g. Shanmugan & Higgins, 1988), offshore Brazil (De Luca et al, 2017; Fernández‐Ibáñez, Jones, et al, 2022; Lima et al, 2020) and Tarim Basin in China (Dong et al, 2018; Wei et al, 2021; You et al, 2018).…”

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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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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Excess permeability in the Brazil pre-Salt: Nonmatrix types, concepts, diagnostic indicators, and reservoir implications

Cited by 20 publications

References 0 publications

Three‐dimensional stratigraphic architecture, secondary pore system development and the Middle Pleistocene transition, Sandy Point area, San Salvador Island, Bahamas

Three‐dimensional stratigraphic architecture, secondary pore system development and the Middle Pleistocene transition, Sandy Point area, San Salvador Island, Bahamas

Geological Insights from Porosity Analysis for Sustainable Development of Santos Basin’s Pre-Salt Carbonate Reservoir

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

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