Microstructural Analysis from X-ray CT Images of the Brae Formation Sandstone, North Sea

Paul-Ross Thomson, Rory Ellis, Domenico Chiarella, Saswata Hier-Majumder

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During deposition and subsequent diagenesis, reservoir rocks develop sediment texture and cement phases are formed during the precipitation of secondary minerals such as microcrystalline quartz, calcite and clay fibrous over-growths that contain secondary porosity. The grain size distribution and presence of secondary microporous material can influence the reservoir porosity and permeability. Using 3D X-ray microtomographic images we analyze the grains and pore space in Brae Formation sandstones from the South Viking Graben in the North Sea. The samplesderived from two cored wells (16/7b-20 and 16/7b-23), and located within the depth interval between 4040 m and 4064 m-display mean grain sizes between 315-524 microns (1.78-1.05 φ units), classifying them as predominantly medium-grained sands, with moderate to well sorting (0.51-0.7 φ units). From our models we calculate the upper and lower bounds of the micropores on the pore connectivity and permeability. Our samples show total porosities between 10 and 18% of which 6 and 13% are effective, leading to a permeability range between 1 and 400 mD through the effective macropore network. We found that the fraction of effective porosity and effective permeability shows a nonlinear reduction with increase in microporous cement volume fraction. Above a threshold cement volume of approximately 5.5% the effective pore network is disconnected and percolation is no longer possible. Based on our observations and modeling results we propose that cement precipitation can be a positive consequence of mineral trapping from sequestered CO2 , which can be important for reducing reservoir quality and ensuring efficient long term storage.
Original languageEnglish
Article number246
Pages (from-to)1-10
Number of pages10
JournalFrontiers in Earth Science
Publication statusPublished - 2 Jul 2020


  • Digital Rock Physics
  • 3D Grain Size
  • Porosity
  • Brae Formation Sandstone,
  • Permeability
  • Petrophysics
  • Microporosity
  • Cementation

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