Computer axial tomography in geosciences: an overview

Computer axial tomography (CAT) is one of the most adequate non-destructive techniques for the investigation of the internal structure of a large category of objects. This method, based on the attenuation of X- or gamma-ray, generates digital images which map the numerical values of the linear attenuation coefficient of a section or of the entire volume of the investigated sample. Depending on the energy of the utilized radiation as well as on the effective atomic number of the sample, CAT can furnish, with a spatial resolution of 0.01-0.5 mm, quantitative as well as qualitative information concerning local density or chemical composition of the sample. In geosciences, CAT has been successfully applied to the investigation of bulk density, moisture content or macroporosity of the soil, soil-plant-water system, oil sand or shales, small scale heterogeneities in siltstone or sandstone, diamonds in kimberlite, mineralization layers in manganese nodules, local structure of marine sediments or coal composition. The method has also been used for the investigation of the rock mechanical properties, rock permeability, fracture network, two or three-phase flow or residual oil distribution in carbonate cores. A review of the actual applications of CAT in soil science, sedimentology, coal geology as well as rock mechanics is presented. All these applications reveal the great potential of CAT in geoscience investigations. (C) 1999 Elsevier Science B.V. All rights reserved.