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Solid Earth An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Mar 2019

Research article | 11 Mar 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

Evaluating porosity estimates for sandstones based on X-ray micro-tomographic images

Mathias Nehler1, Ferdinand Stoeckhert2, Anne Oelker3, Jörg Renner2, and Erik Saenger1,2 Mathias Nehler et al.
  • 1International Geothermal Centre, Bochum University of Applied Sciences, 44801, Germany
  • 2Ruhr-Universität, Bochum, 44801, Germany
  • 3RWTH Aachen, Aachen, 52062, Germany

Abstract. We compare experimentally determined porosity with values derived from X-ray tomography for a suite of eight sandstone varieties covering a porosity range from about 3 to 25 %. In addition, we performed conventional stereological analysis of SEM images and examined thin sections. We investigated the sensitivity of segmentation, the conversion of the tomographic gray-value images representing the obtained X-ray attenuation coefficients into binary images, to (a) resolution of the digital images, (b) denoising filters, and (c) seven thresholding methods. Images of sandstones with porosities of 15 to 25 % exhibit a bimodal intensity distribution of the attenuation coefficients, enabling unambiguous segmentation that gives porosity values closely matching the laboratory values. For samples with lower porosities, pores and grains do not separate well in the skewed unimodal intensity histograms. For these samples, all tested thresholding methods tend to miscalculate porosity significantly. In addition to absolute porosity, the ratio between pore size and resolution, and mineralogical composition of the rocks affect the biases of the global segmentation methods.

Mathias Nehler et al.
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Mathias Nehler et al.
Mathias Nehler et al.
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Short summary
The technique of X-ray computed tomography (CT) is widely used in multiple disciplines such as medicine, industry and earth sciences. However, quantitative analysis from the reconstructed images are subject to errors due to technical limitations and subsequent evaluation workflows. The paper addresses the uncertainties related to the estimation of porosity from these images and compares the results with laboratory measurements. Accurate porosity estimates are linked to sufficient resolution.
The technique of X-ray computed tomography (CT) is widely used in multiple disciplines such as...