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Diagenesis and reservoir quality evolution of paleocene deep-water, marine sandstones, the Shetland-Faroes Basin, British Continental Shelf
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
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2008 (English)In: Marine and Petroleum Geology, ISSN 0264-8172, Vol. 25, no 6, 514-543 p.Article in journal (Refereed) Published
Abstract [en]

The Palaeocene, deep-water marine sandstones recovered from six wells in the Shetland-Faroes Basin represent lowstand, transgressive and highstand systems tract turbiditic sediments. Mineralogic, petrographic, and geochemical analyses of these siliciclastics are used to decipher and discuss the diagenetic alterations and subsequent reservoir quality evolution. The Middle-Upper Palaeocene sandstones (subarkoses to arkoses) from the Shetland-Faroes Basin, British continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates, quartz and clay minerals. Carbonate cements (intergranular and grain replacive calcite, siderite, ferroan dolomite and ankerite) are of eogenetic and mesogenetic origins. The eogenetic alterations have been mediated by marine, meteoric and mixed marine/meteoric porewaters and resulted mainly in the precipitation of calcite (δ18OV−PDB=−10.9‰ and −3.8‰), trace amounts of non-ferroan dolomite, siderite (δ18OV−PDB=−14.4‰ to −0.6‰), as well as smectite and kaolinite in the lowstand systems tract (LST) and highstand systems tract (HST) turbiditic sandstone below the sequence boundary. Minor eogenetic siderite has precipitated between expanded and kaolinitized micas, primarily biotite. The mesogenetic alterations are interpreted to have been mediated by evolved marine porewaters and resulted in the precipitation of calcite (δ18OV−PDB=−12.9‰ to −7.8‰) and Fe-dolomite/ankerite (δ18OV−PDB=−12.1‰ to −6.3‰) at temperatures of 50–140 and 60–140 °C, respectively.

Quartz overgrowths and outgrowth, which post- and pre-date the mesogenetic carbonate cements is more common in the LST and TST of distal turbiditic sandstone. Discrete quartz cement, which is closely associated with illite and chlorite, is the final diagenetic phase. The clay minerals include intergranular and grain replacive eogenetic kaolinite, smectite and mesogenetic illite and chlorite. Kaolinite has been subjected to mesogenetic replacement by dickite. The K-feldspar and plagioclase grains have been albitized. Dissolution of calcite cement and of framework grain (feldspar, volcanic fragments and mud intraclasts) has resulted in a considerable enhancement of reservoir quality.

Place, publisher, year, edition, pages
2008. Vol. 25, no 6, 514-543 p.
Keyword [en]
Diagenesis, Turbidites, Reservoir quality, Tertiary, Shetland-Faroes Basin, Sequence stratigraphy
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95536DOI: 10.1016/j.marpetgeo.2007.07.012ISI: 000257533300005OAI: oai:DiVA.org:uu-95536DiVA: diva2:169792
Available from: 2007-03-01 Created: 2007-03-01 Last updated: 2009-10-19Bibliographically approved
In thesis
1. Diagenesis and Reservoir-Quality Evolution of Deep-Water Turbidites: Links to Basin Setting, Depositional Facies, and Sequence Stratigraphy
Open this publication in new window or tab >>Diagenesis and Reservoir-Quality Evolution of Deep-Water Turbidites: Links to Basin Setting, Depositional Facies, and Sequence Stratigraphy
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A study of the distribution of diagenetic alterations and their impact on reservoir-quality evolution in four deep-water turbidite successions (Cretaceous to Eocene) from basins in active (foreland) and passive margins revealed the impact of tectonic setting, depositional facies, and changes in the relative sea level.

Diagenetic modifications encountered in the turbiditic sandstones from the passive margin basins include dissolution and kaolinitization (kaolin has δ18OV-SMOW = +13.3‰ to +15.2‰; δDV-SMOW = -96.6‰ to -79.6‰) of framework silicates, formation of grain coating chloritic and illitic clays, cementation by carbonates and quartz, as well as the mechanical and chemical compaction of detrital quartz. Kaolinitization, which is most extensive in the lowstand systems tracts, is attributed to meteoric-water flux during major fall in the relative sea level. Preservation of porosity and permeability in sandstones from the passive margin basins (up to 30% and 1 Darcy, respectively) is attributed to the presence of abundant rigid quartz and feldspar grains and to dissolution of carbonate cement as well as mica and feldspars. Diagenetic modifications in turbidites from the foreland basins include carbonate cementation and mechanical compaction of the abundant ductile rock fragments, which were derived from fold-thrust belts. These diagenetic alterations resulted in nearly total elimination of depositional porosity and permeability.

The wide range of δ13CV−PDB values of these cements (about -18‰ to +22‰) in passive margin basins is attributed to input of dissolved carbon from various processes of organic matter alterations, including microbial methanogenesis and thermal decarboxylation of kerogen. The narrower range of δ13CV−PDB values of these cements (about -2‰ to +7‰) in the foreland basins suggests the importance of carbon derivation from the dissolution of carbonate grains. The generally wide range of δ18O values (about -17‰ to -1‰) of the carbonate cements reflect the impact of oxygen isotopic composition of the various fluid involved (including marine depositional waters, fluxed meteoric waters, evolved formation waters) and the wide ranges of precipitation temperatures.

Results of this study are anticipated to have important implication for hydrocarbon exploration in deep-water turbidites from passive and active margin basins and for pre-drilling assessment of the spatial and temporal distribution of reservoir quality in such deposits.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 279
Keyword
Bedrock geology, Diagenesis, reservoir quality, active margin, passive margin, depositional facies, sequence stratigraphy, Berggrundsgeologi
Identifiers
urn:nbn:se:uu:diva-7634 (URN)978-91-554-6817-0 (ISBN)
Public defence
2007-03-23, Axel Hamberg-salen, Geocentrum, 10:00 (English)
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Available from: 2007-03-01 Created: 2007-03-01 Last updated: 2009-03-24Bibliographically approved

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