Calibration Of Dual Energy Ct Scans For Rock Core Examination

One of the first applications of X-ray computed tomography in geology took place in 1974. X-ray tomography (CT) allows non-invasive imaging of the examined objects. The result of a tomographic measurement is a spatial image, showing the changes in X-ray absorption value for each point of the examined object, which are a result of calculations during the reconstruction process. An important advantage of computer tomographs is the ability to test large objects (meter sections of the core) in a very short time, while the disadvantage is the relatively low resolution of the measurement. Each voxel in the tomographic image has a specific grey value, proportional to the linear attenuation coefficient, depending on the electron density and the effective atomic number averaged in the imaged space (the averaging range is determined by the resolution of the tomographic image). Two tomographic images registered at two different energies, allows the deconvolution of the images into two components: the first - dependent on the electron density and the second - dependent on the effective atomic number. The aim of this study is to show the possibility of using dual energy computed tomography (DECT) to litho-density characterization of rock cores. In order to use tomographic images to obtain the above-mentioned physicochemical values, it is necessary to standardize CT images. The paper presents the process of determining calibration coefficients, which are necessary to convert the values of absorption coefficients, which are a direct result of CT reconstruction, into density values and effective Z atomic number. The article presents the calibration process with the use of reference rock fragments. The values of the standard samples computed from the analysis of images were compared with the values determined by laboratory methods. An example of the application of results is presented on the examined part of the image of the sandstone core, containing a calcite-filled fracture.