Texture and Recognition of Secondary Porosity in Sandstones

Schmidt, Volkmar; McDonald, David A.

doi:10.2110/pec.79.26.0209

Cited by 92 publications

(72 citation statements)

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“…2). Porosity is mainly secondary in origin, as evidenced by the presence of corroded grains, intra constituent pores, inhomogeneity of packing and partial dissolution (Schmidt and McDonald 1979b). Intergran ular, oversized and intragranular porosity have all been identifi ed, originating mainly from dissolution of car bonate cements (mean of 7.1 %) and K-feldspar grains (mean of 3%).…”

Section: Secondary Porositymentioning

confidence: 99%

Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain

Ochoa

Arribas

2005

Int J Earth Sci (Geol Rundsch)

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Buntsandstein deposits generated in a slowly subsiding basin on the western margin of the Iberian Chain are represented by a stratigraphic succession of fluvial deposits less than 100 m thick (conglomerates, sandstones, and shales). Diagenetic processes in sand stones can be grouped as eodiagenetic, mesodiagenetic, and telodiagenetic. Eodiagenesis can be associated with Muschelkalk, Keuper, and probably early Juras sic times. Mesodiagenesis is probably related to Jurassic times. Diagenetic chemical reactions suggest a maximum burial less than 1.5 km and low tempera tures « 120°C). Patterns of porosity reduction by compaction and cementation suggest four diagenetic stages: (1) Loss of primary porosity by early mechanical compaction; (2) early cementation (K feldspar and dolomite); (3) dissolution of cements; and (4) framework collapse by re-compaction. These stages are manifested by the presence of two types of sand stone. Type I sandstones present high intergranular volume (mean, 30%). Type II sandstones are charac terized by high compactional porosity loss and exhibit low values of intergranular volume (mean, 16.9%). Type 11 sandstones are associated with the dissolution of cement and later re-compaction of type I sand stones. An intermediate telodiagenetic phase is de duced and related to the sharp unconformity between Lower Cretaceous sediments and the underlying sedi ments. This suggests that a mechanically unstable framework collapsed during the Cretaceous, generating type II sandstones. The analyzed diagenetic paths have a wide applicability on similar marginal areas of rift basins.

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Section: Secondary Porositymentioning

confidence: 99%

Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain

Ochoa

Arribas

2005

Int J Earth Sci (Geol Rundsch)

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“…This reveals that the formation of these grain coatings occurred during early diagenesis through iron oxide rich pore-water. At this stage, oxidizing conditions in the interstitial waters must have existed to allow for the formation of iron cement since the chemistry of the interstitial waters was primarily controlled by the depositional environment as documented by Schmidt and McDonald [40,41].…”

Section: Early Diagenetic Stagementioning

confidence: 99%

Diagenesis and Reservoir Properties of the Permian Ecca Group Sandstones and Mudrocks in the Eastern Cape Province, South Africa

2017

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Diagenesis is one of the most important factors that affects reservoir rock property. Despite the fact that published data gives a vast amount of information on the geology, sedimentology, and lithostratigraphy of the Ecca Group in the Karoo Basin of South Africa, little is known about the diagenesis of the potentially feasible or economically viable sandstones and mudrocks of the Ecca Group. This study aims to provide an account of the diagenesis of sandstones and mudstones from the Ecca Group. Twenty-five diagenetic textures and structures were identified and grouped into three stages that include early diagenesis, burial diagenesis and uplift-related diagenesis. Clay minerals are the most common cementing materials in the sandstones. Smectite, kaolinite, and illite are the major clay minerals that act as pore lining rims and pore-filling materials. A part of the clay minerals and detrital grains was strongly replaced by calcite. Calcite precipitates locally in the pore spaces and partially or completely replaced clay matrix, feldspar, and quartz grains at or around their margins. Precipitation of cements and formation of pyrite and authigenic minerals occurred during the early diagenetic stage. This process was followed by lithification and compaction which brought about an increase in tightness of grain packing, loss of pore spaces, and thinning of bedding thickness due to overloading of sediments and selective dissolution of the framework grains. Mineral overgrowths, mineral replacement, clay-mineral transformation, dissolution, deformation, and pressure solution occurred during burial diagenetic stage. After rocks were uplifted, weathered and unroofed by erosion, this resulted in decementation and oxidation of iron-rich minerals. The rocks of the Ecca Group were subjected to moderate-intense mechanical and chemical compaction during their progressive burial. Intergranular pores, secondary dissolution, and fractured pores are well developed in the sediments of the Ecca Group. The presence of fractured and dissolution pores tend to enhance reservoir quality. However, the isolated nature of the pore linkage makes them unfavorable producers of hydrocarbons, which at best would require stimulation. The understanding of the space and time distribution of diagenetic processes in these rocks will allow the development of predictive models of their reservoir quality, which may contribute to the reduction of risks involved in hydrocarbon (oil and gas) exploration.

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“…Foram coletadas 13 amostras (seis de calcários e sete de arenitos) para análise petrográfica com microscópio de luz polarizada. As análises seguiram critérios texturais e mineralógicos convencionais de descrição e interpretação de calcários (Folk, 1962;Dunham, 1962;Choquette e Pray, 1970;Logan et al, 1969;Wilson, 1975) e arenitos (Dott Junior, 1964;Griffiths, 1967;Folk, 1968Folk, , 1974Dickinson, 1970;Pettijohn et al, 1987;Schmidt et al, 1977;Nichols, 2009).…”

Section: Materiais E Métodosunclassified

Análise de fácies e petrografia de uma seção do Membro Crato em Nova Olinda (CE): contribuições à história deposicional e diagenética do neoaptiano na Bacia do Araripe

Santos

Azevedo

Nascimento

et al. 2017

Geol. USP. Sér. Cient.

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Na Bacia do Araripe, o Membro Crato é uma das mais importantes unidades estratigráficas por seu conteúdo fossilífero, seu contexto análogo ao das “Camadas Pré-Sal” e seu aproveitamento econômico como material de revestimento. Neste trabalho, análises de fácies e petrográficas foram combinadas no estudo de uma seção do Membro Crato em Nova Olinda (CE), com o intuito de investigar sua história deposicional e diagenética. Para tanto, a faciologia de uma seção colunar contínua de cerca de 70 m de espessura foi analisada com a coleta de 13 amostras de rochas carbonáticas, siliciclásticas e evaporíticas. As amostras foram analisadas por petrografia ótica. Foram descritas cinco fácies deposicionais: lamito margoso (Lm), calcilutito laminado (Cl), arenito maciço (Am), siltito com laminação cruzada cavalgante (Scc) e evaporito colunar (Ec). As fácies mais espessas e recorrentes foram interpretadas como lacustres (Lm, Cl), seguidas de sucessões aluviais (Am, Scc) em meio aos intervalos lacustres. A sucessão termina com indícios faciológicos de que condições de extrema aridez (Ec) foram atingidas ao final do intervalo descrito. A petrografia, aqui focada em rochas das fácies Cl, Am e Scc, reforça a ideia de que o intervalo do Aptiano local correspondia a um sistema lacustre árido, eventualmente alimentado por fluxos aluviais imaturos a partir de áreas-fontes próximas. Em particular, o baixíssimo grau de compactação mecânica e cimentação incipiente das rochas terrígenas sugere que a sucessão foi pouco afetada por diagênese após seu soterramento, que foi, por essa razão, pouco profundo. A semelhança dos intervalos terrígenos do Membro Crato com aqueles descritos para a porção final da sotoposta Formação Barbalha sugere contemporaneidade com passagem transicional retrogradante entre as duas unidades.

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Texture and Recognition of Secondary Porosity in Sandstones

Cited by 92 publications

References 0 publications

Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain

Diagenetic paths in the margin of a Triassic Basin: NW zone of the Iberian Chain, Spain

Diagenesis and Reservoir Properties of the Permian Ecca Group Sandstones and Mudrocks in the Eastern Cape Province, South Africa

Análise de fácies e petrografia de uma seção do Membro Crato em Nova Olinda (CE): contribuições à história deposicional e diagenética do neoaptiano na Bacia do Araripe

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