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Abstract Non-transparency of microstructures for the porous media has long been the obstacle for a deep understanding of the mechanisms of rock damage and coal and rock outbursts at depth. As an attempt，a methodology based on wavelet multi-resolution analysis(MRA) for visualization and multiscale-anisotropic-detailed characterization of pore space for complex porous media at meso- and microscopic scales is proposed. In order to validate the proposed approach，observations are made on the six groups of coal rock specimens by using scanning electron microscope(SEM)，sampled from six different underground mining districts；the integrated image processing schemes are conducted for the so called“sub-pixel”scale analysis of the resulting SEM images，including multi-scale wavelet transform，image segmentation and reconstruction. The detail sub-bands coefficients of the wavelet transform are used to reconstruct images of the horizontal，vertical and diagonal dominant micropores of the microporous matrix. In addition，the probability density distribution of the characteristic length for the pore throat and cavity，the porosity and fractal dimensions for the pores at multiple scales are calculated. The segmented macro-fractures by the MRA are at micron scale while the micro-pores are at nano-scale. The macro-fractures of all the specimens have much larger fractal dimension value than that of the micro-pores. The profiles of the pore throat distribution for all the specimens take on the shape of single peak，and the peak value is the measure of the drag forces for the fluid transport，whereas the curves of the pore cavity take on the shapes of single or multiple peaks，and the maximal peak value represents the storage capacity for the fluids. The obtained results validate the applicability of the microscopic image based approach for characterization of the geometrical boundary and structural features of fractured rocks，which will certainly contribute to a deep understanding of the influences of the complex pore structures on the nonlinear behaviour of the rock masses at depth.
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Received: 01 November 2009
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