Abutaha S.M., Geiger J., Gulyás S. & Fedor F., 2022: Calculating the representative elementary volume of porosity using X-ray computed tomography: Boda Claystone Formation core sample/Hungary. Acta Geologica Slovaca, 14, 1, 25–36.

Calculating the representative elementary volume of porosity using X-ray computed tomography: Boda Claystone Formation core sample/Hungary

Saja M. Abutaha¹, János Geiger¹, Sándor Gulyás¹ & Ferenc Fedor²

¹University of Szeged, Department of Geology and Paleontology, Egyetem utca 2-6, 6722 Szeged, Hungary; sajaabutaha@geo.u-szeged.hu, matska@geo.u-szeged.hu,gulyas.sandor@geo.u-szeged.hu
²GEOCHEM Ltd, 55/1 Viola Str, 7761 Kozármisleny, Hungary; fedor.ferenc@geochem-ltd.eu

Abstract

The main objective of this study is to calculate the representative elementary volume (REV) according to voxels’ porosity. Physical properties of rock-forming components of a 5 m-long core sample of the Boda Claystone Formation (BCF) were acquired using 3D X-ray computed tomography images. The REV calculation was established using the Autoregressive Integrated Moving Average, Statistical Process Control (ARIMA SPC) technique. This method (ARIMA SPC) was five times iterated by varying positions of starting voxel volume in the core sample: upper left, upper right, lower left, lower right, and middle. The general average range of REV values was from 16.56 cm 3 to 46.26 cm^-3 . Monte Carlo simulation with 1,000 runs was used to simulate the long-run properties of REV and the normalized REV of voxel-porosity. The simulated REV values were 64.80 cm^-3 in the upper left position, 61.44 cm^-3 for the upper right, 55.59 cm^-3 for the lower right, 53.77 cm^-3 for the lower left, and 42.23 cm^-3 for the middle. According to the simulation of the normalised REVs, their volume percentages were as follows: 40% for the upper left, 41.34% in the lower right, 23.86% for the lower left. Lastly, the upper right and the central (middle) positions had almost the same percentage volumes around 15.5%. As the initial volume started from any core sample’s corners, the REV porosity range would be between 2.47% and 2.58%, which is close to the average voxel porosity of BCF (2.55%). However, a deviant (higher) REV porosity value was attained from the centre initiated volume (~2.8%). Therefore, the middle part of the studied core sample might not be adequate to be considered as an initial voxel volume of the REV calculation.

Key words: Hounsfield unit (HU), voxel porosity, Autoregressive Integrated Moving Averages (ARIMA), Statistical Process Control (SPC), representative elementary volume (REV)

Manuscript received: 2021-12-16

Revised version accepted: 2022-05-05