Micro-CT image calibration to improve fracture aperture measurement

• Published in: Case studies in nondestructive testing and evaluation Vol. 6; pp. 4 - 13
• Main Authors: Ramandi, Hamed Lamei, Armstrong, Ryan T., Mostaghimi, Peyman
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2016
• ISSN: 2214-6571; 2214-6571
• DOI: 10.1016/j.csndt.2016.03.001

A novel technique for the accurate measurement and adjustment of fracture apertures in digital images of fractured media is presented. We utilize X-ray micro-computed tomography to image a highly fractured coal sample and collect high-resolution scanning electron microscope (SEM) images from the samples surface to facilitate segmentation of coal fractures. The gray-scale micro-CT values at the mid-point of fractures are obtained and correlated to aperture sizes measured with the higher resolution SEM data. Afterwards, the micro-CT images are upsampled to enable assignment of aperture sizes smaller than the image resolution. We initially segment the coal image, upsample the segmented image, and then re-calibrate the fracture aperture sizes. The final calibrated segmented image contains the fracture network acquired from the micro-CT data with precise aperture sizes assigned based on the high-resolution SEM data. To illustrate the importance of accurate aperture measurement, two coal subsets are tested. The permeabilities before and after applying the calibration method are measured. The results show a significant change in numerical permeabilities after applying the calibration method. This indicates that a large amount of information is potentially omitted when utilizing standard image segmentation tools to segment fractured media.