Preprints
https://doi.org/10.5194/se-2019-48
https://doi.org/10.5194/se-2019-48

  11 Mar 2019

11 Mar 2019

Review status: this preprint was under review for the journal SE. A final paper is not foreseen.

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.

This preprint has been withdrawn.

Mathias Nehler et al.

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Mathias Nehler et al.

Mathias Nehler et al.

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This preprint has been withdrawn.

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.