The Porosity-Preserving Effects of Microcrystalline Quartz Coatings in Arenitic Sandstones: Examples from the Norwegian Continental Shelf

  1. Richard H. Worden3 and
  2. Sadoon Morad4
  1. J. Jahren1 and
  2. M. Ramm2

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304237.ch18

Quartz Cementation in Sandstones

Quartz Cementation in Sandstones

How to Cite

Jahren, J. and Ramm, M. (2009) The Porosity-Preserving Effects of Microcrystalline Quartz Coatings in Arenitic Sandstones: Examples from the Norwegian Continental Shelf, in Quartz Cementation in Sandstones (eds R. H. Worden and S. Morad), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304237.ch18

Editor Information

  1. 3

    School of Geosciences, The Queen's University, Belfast, BT7 1NN, UK

  2. 4

    Sedimentary Geology Research Group, Institute of Earth Sciences, Uppsala University, Norbyvägen 18 B, S–75236, Uppsala, Sweden

Author Information

  1. 1

    Department of Geology, University of Oslo, P. O. Box 1047, Blindern, N-0316 Oslo, Norway

  2. 2

    Norsk Hydro Exploration, N-1321 Stabekk, Norway

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 3 MAR 2000

ISBN Information

Print ISBN: 9780632054824

Online ISBN: 9781444304237

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Keywords:

  • porosity-preserving effects of microcrystalline quartz coatings in arenitic sandstones;
  • quartz cementation - important porosity reducing process in burial diagenesis;
  • redistribution of quartz in sandstones;
  • quartz solubility in formation waters;
  • pressure dissolution along stylolites - contributing silica during normal diagenesis

Summary

Microcrystalline quartz coatings on detrital quartz grains are not uncommon in reservoir sandstones from the Norwegian continental shelf. The present burial depths for these sandstones range between 4150 and 4419 m. Effective pressures in the reservoirs range between 20 and 40 MPa. Scanning electron microscope investigation reveals various amounts and developments of macrocrystalline quartz overgrowths coexisting with the microcrystalline variety. The microcrystalline quartz crystals are between 0.5 and 5 µm in diameter with an average diameter around 1.5 µm. Authigenic quartz crystals larger than this are always in optical continuity with the detrital quartz. The presence of microcrystalline quartz in the system indicates that the porewater has been oversaturated with respect to macroquartz and microcrystalline quartz. The microcrystalline quartz coatings hindered quartz cementation and slowed down pressure dissolution. The reason for this is that pressure dissolution controlled quartz supersaturation, without effective reprecipitation or removal of silica from the system (system size, 10–100 m), will result in an elevated supersaturation of silica, balancing further pressure dissolution. In such situations porosity will be preserved to greater burial depths than expected.