A Very Different Barremian-Aptian Lacustrine Pre-Salt Facies Association: Biotic Self-Organization In BMC-33, Outer Basin Campos Basin, Brazil

Hunt, Dave; Luca, Pedro Henrique Vieira de; Gomis‐Cartesio, Luz E.; Lapponi, F.; Masiero, Isabella; Waldum, A.; Chandler, A. S.; Matias, J.L. De Lima; Hess, C.; Fonseca, Julia

doi:10.3997/2214-4609.201982102

Cited by 4 publications

(2 citation statements)

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“…Muniz & Bosence (2015), from a very small data set from the Macabu Formation (the BVF equivalent) in south Campos Basin, record possible microbialites, and Hunt et al . (2019) also report microbialites from that basin. These studies raise the possibility that microbialites may be locally more significant in both Santos and Campos basins.…”

Section: Compositionmentioning

confidence: 91%

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The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Wright

2020

Sedimentology

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During the Aptian (Cretaceous), in what is now the South Atlantic, the largest chemogenic (abiotic) carbonate factory so far identified in the Phanerozoic geological record developed as a vast hyper‐alkaline lake system. This covered at least 330 000 km2, producing carbonates, locally over 500 m thick, in what are now the offshore Santos and Campos basins (Brazil), and Kwanza Basin (Angola). Current evidence supports the view that almost all of this carbonate was chemogenic in origin, precipitated from hyper‐alkaline, shallow lake waters, probably by evaporation. This unit, best documented from offshore Brazil and known as the Barra Velha Formation (Santos Basin) and the Macabu Formation (Campos Basin), consists of just two basic carbonate components, millimetre to centimetre sized crystal shrubs and spherulites. These are commonly in situ but can also be reworked into a range of detrital facies. Demonstrable microbialites are generally rare. These carbonates are associated with Mg silicates (as clays) which had a profound influence not only on the textural development of the in situ carbonates, but also on their diagenesis. The dissolution of the clays produced much of the porosity in these limestones, which are the hosts for multi‐billion barrel oil fields. The source of the carbonate was most likely from metasomatic alteration of mafic rocks, such as continental flood basalts related to Atlantic opening, with some contribution from much older continental basement. Clear evidence that serpentinization of possible exhumed mantle is lacking but mantle CO2 is likely to have been a critical factor in determining the composition of the fluids from which the carbonates formed and the high alkalinities of the lake waters.

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Section: Compositionmentioning

confidence: 91%

“…Araujo et al (2012), and the Cod o Formation of the Parnaiba Basin by Bahniuk et al (2015). Hunt et al (2019) report biogenic microbialites and breccias deposited in a range of saline to alkaline lake waters from Campos Basin, represented by diverse microbial and related features not seen in the BVF and its equivalents.…”

Section: Geological Settingmentioning

confidence: 99%

The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Wright

2020

Sedimentology

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Open fractures in pre-salt silicified carbonate reservoirs in block BM-C-33, the Outer Campos Basin, offshore Brazil

Wennberg

McQueen

Luca³

et al. 2021

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Natural open fractures are present in sidewall cores and in whole core samples from pre-salt reservoirs in the license BM-C-33 in the Campos Basin, Brazil. Open fractures are also observed in borehole image logs, and fracture densities are in general high. The highest density of open fractures is seen in the damage zones above and below larger cavities (Amalgamated Cavern Damage Zones - ACDZs). Outside the ACDZs the fracture density is high in silicified carbonates, where it tends to increase with decreasing porosity. Clean dolomites are less fractured than the silicified interval while the less brittle argillaceous dolomites have the lowest fracture density. Some fractures appear vuggy on borehole image logs and fracture densities are high close to vugs and larger cavities. The positive correlation between fractures and vugs is caused by flow of dissolving fluids through open fractures, and fracturing at stress concentrations around vugs, Two major fault zones have been interpreted from borehole image logs which have damage zones with very high fracture density. The well test permeability is much greater than the matrix permeability estimated from sidewall core and log measurements. This excess permeability is attributed to fractures, in combination with caverns and intervals with frequent vugs.

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Fracture analysis in borehole images from BM-C-33 area, outer Campos Basin, Brazil

Brandão,

Wennberg,

Borghi

et al. 2024

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In the BM-C-33 area, divided into the Raia Manta and Raia Pintada development areas, reservoirs are arranged into three structural highs: Gávea, Seat, and Pão de Açúcar. These reservoirs consist of Pre-salt limestones deposited on volcanic sequences and underwent complex diagenetic evolution. Successive post-depositional processes, including silicification, affected original mineral assemblage, modified pore textures, and caused intense fracturing. Based on borehole image logs (BHI), wireline data from four wells, and 2D and 3D seismic data, this study details natural fracture acoustic and resistivity properties. It also discusses the relationship of faults, fractures, and vugs with diagenetic and tectonic processes. The authors used the data to divide the Pre-salt section (Cabiúnas and Macabu formations) into three informal stratigraphic units. The analysis of interpreted fractures within these units suggests that major fracturing occurred due to regional tectonic stress, with local aspects like structural positioning interfering. The results of the fracture analysis imply a direct relationship between fracturing and silicification. Additionally, fracture density, vug volume distribution, and the presence of dissolution features like enlarged fractures limited to specific units imply stratigraphic control on fluid percolation. Finally, the study examines structural particularities in BM-C-33 area that potentially impacted intensity and extension of diagenetic alterations.

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A Very Different Barremian-Aptian Lacustrine Pre-Salt Facies Association: Biotic Self-Organization In BMC-33, Outer Basin Campos Basin, Brazil

Cited by 4 publications

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The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Open fractures in pre-salt silicified carbonate reservoirs in block BM-C-33, the Outer Campos Basin, offshore Brazil

Fracture analysis in borehole images from BM-C-33 area, outer Campos Basin, Brazil

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A Very Different Barremian-Aptian Lacustrine Pre-Salt Facies Association: Biotic Self-Organization In BMC-33, Outer Basin Campos Basin, Brazil

Cited by 4 publications

References 0 publications

The mantle, CO2and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

The mantle, CO2and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

Open fractures in pre-salt silicified carbonate reservoirs in block BM-C-33, the Outer Campos Basin, offshore Brazil

Fracture analysis in borehole images from BM-C-33 area, outer Campos Basin, Brazil

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The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born

The mantle, CO₂and the giant Aptian chemogenic lacustrine carbonate factory of the South Atlantic: Some carbonates are made, not born