Quantifying Variability of Physical/Petrophysical Properties of Boda Claystone Formation (BCF) Using X-Ray Computed-Tomography Scan Images (CT)

• Main Author: Abutaha, Saja Mohammad Ahmed
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022
• Subjects: Geology; Lithology; Mineralogy; Minerals; Permeability; Porosity; Rocks; Sediments
• ISBN: 9798380407472

The Upper Permian Boda Claystone Formation (BCF) is located in the Western Mecsek Mountains (WM Mts), Southern Transdanubia, SW Hungary. The Mecsek Mountains are part of the Tisza Mega unit. This unit, which forms a colossal lithosphere fragment (more than 100,000 km2 ), was detached from the southern margin of Variscan Europe during the Jurassic (Haas & Péró 2004; Balla 1987; Horváth 1993) and settled eventually in the Pannonian Basin.In this work, an X-ray computed tomography (CT) technique is employed to acquire high-resolution 3D images from the 5m core sample. The study objectives recapitulate into five prominent points: 1) calculate and visualize the voxel porosities of each rock-forming component. 2) classify the porosities of voxels into the optimal number of clusters. 3) define rock-forming components by porosity clusters and visualize their distributions. 4) quantify and evaluate the minimum volume of a core sample of the BCF that captures a representative quantity of its physical heterogeneity (i.e., density). Finally, 5) assess the minimum volume of a core sample of the BCF that can evaluate a representative quantity of its petrophysical heterogeneity (i.e., voxel porosity). A core sample of BCF (Ib-4), about 5 m-long, was scanned at the Institute of Diagnostic Imaging and Radiation Oncology, University of Kaposvar, Hungary. X-ray computed tomography (CT) can reveal internal, three-dimensional details of objects in a non-destructive way and provide high-resolution, quantitative data in the form of CT numbers. The CT measurements were performed on a Siemens Emotion 6 medical scanner. The instrument operates at 120 kVp (peak kilovoltage), with 250 mAs (milliampere-seconds) current, and 1.0 s (sampling intervals). The lateral resolution was (0.1953 × 0.1953) mm2 with 1.25 mm of scanslice thickness. The image reconstruction matrix was 512 × 512 pixels. The field of view (FOV) was approximately 9.99 cm. CT images are stored in a DICOM (Digital and Imaging Communications in Medicine) format. A 3D-nearest neighbor algorithm was used to build the 3D volumes of the scanned core blocks. This process resulted in two lattices, one for the vacuum dried and one for the saturated core volumes. The so-called scanning artifacts may obscure details of interest or cause the CT value of a single material to change in different parts of an image. The most commonly encountered artifact in CT scanning is beam hardening. Various methods have been developed to reduce or remove the effects of beam hardening. One of these is a subset of the CT volumes. It means removing the 3D image’s outer edges; only central volumes are handled in quantitative analysis. For the identification of rock-forming components of the core sample, CT HU intervals defined by PURAM for characteristic rock types of BCF were used as follows: detrital fragments (coarse siltstone): < 2700 HU, fine siltstone: 2700–3150 HU, claystone: 3150–3300 HU, calcite and/or dolomite: 3300–3600 HU, and albite: > 3600 HU. The reality of the rock-forming components was compared with macroscopic core descriptions. Calculating the relative percentages of the rock-forming components for scanned core parts was a prerequisite for defining small-scale layers (CT layers). The above information has been introduced in chapter 1.