Development of early diagenetic silica and quartz morphologies — Examples from the Siri Canyon, Danish North Sea: examples from the Siri Canyon, Danish North Sea

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  • Rikke Weibel, Department of Geological Mapping, Geological Survey of Denmark and Greenland, Denmark
  • Henrik Friis
  • Afsoon Moatari Kazerouni, Denmark
  • Johan B. Svendsen, DONG Energy, Exploration and Production, Denmark
  • Jesper Stokkendal, DONG Energy, Exploration and Production, Denmark
  • Mette Lise Kjær Poulsen, DONG Energy, Exploration and Production, Denmark
  • Section for Sedimentary Geology
  • Department of Earth Sciences
The Siri Canyon has proved to be a perfect area for investigating various morphologies of diagenetic silica in
sandstones. The development in silica morphologies can be observed from very shallow (∼1700 m) to increased
burial depth (∼3000 m)and increased proximity to the Central Graben (distance from0 to 65 km).Hydrocarbons
and pore fluids, now found in the Siri Fairway, have (at least partly) originated from the Central Graben.
The Siri Canyon is a submarine canyon system eroded into the uppermost chalk deposits and filled with
Palaeogene hemipelagic and turbiditic marls and mudstones interbedded with sandstone units deposited from
sandy mass-flows and sandy turbidites, which originated on the Stavanger Platform. Several hydrocarbon
exploration and production wells have been drilled in the Siri Canyon, seven of which are included in this study
(Nini-3, Nini-1, NA-2P, Sofie-1, Siri-4, Celilie-1A and Augusta-1). The reservoir sandstones in these wells all
contain authigenic silica of various morphologies identifiedwith a combination of traditional optical microscopy
and scanning electron microscopy.
The silicamorphologies in some places are classic andwell-documented in the literature, whereas others, at least
to our knowledge, have never previously been described. Some of the silica morphologies presented here show
gradual transition from one to another, and others are stand-alone forms without clear relationships to other
forms.
The silica morphologies can be expressed in the following way:
1. Opal rims; characteristic of the initial phase of the silica diagenesis in most sandstone units in the Siri
Canyon. Thick opal rims characterise the sandstone parts adjacent to the mudstone units in the Stine
segment of the Siri Field.
2. Microquartz (quartz crystals with a size of 1–5 μm); seen as coatings on the opal rims, both ordered and
random.
3. Cavity overgrowth; found as quartz outgrowths in circular and angular cavities formed by dissolution of
early authigenic phases. Angular cavities in the microquartz coatings origin from dissolution of
clinoptilolite, possibly with a source in volcanic ash, whereas dissolution of lepispheres probably resulted
in circular cavities.
4. Quartz ridges (syntaxial quartz overgrowths, a few micro millimetre in width, in parallel lines — defined
in this paper).
5. Quartz mountains (syntaxial, irregular 5–10 μm large quartz crystals — defined in this paper); developed
in the water-filled sandstone intervals where fluids from the Central Graben were introduced, possibly
together with the hydrocarbon, and where the continued growth was not retarded by the presence of
hydrocarbons in the pore fluids.
6. Macroquartz (syntaxial quartz overgrowths N20 μm); seen as continued growths from quartz mountains.
This takes place in the deeper reservoir sandstones, promoted by fluids originating from the Central
Graben and increased burial depth.
7. Quartz with sutured grain contacts; occurring only in the deepest well (3000 m).
Original languageEnglish
JournalSedimentary Geology
Volume228
Issue3-4
Pages (from-to)151-170
Number of pages20
ISSN0037-0738
DOIs
Publication statusPublished - 2010

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