X-ray Micro-Computed Tomography (μ-CT) and Scanning Electron Microscope (SEM) was used to analyze the microcracks in cylindrical rock specimens under constant stress state. Marcellus shale specimens were maintained under constant load and terminated at the onset of tertiary creep stage. Specimens were analyzed through X-ray μ-CT and SEM to extract the topological information of sub-critical cracks. X-ray μ-CT scan of the complete specimen in contrast to the SEM showed the two dimensional crack distribution with resolution up to 29.9 microns. Comparison between the time to reach the tertiary creep stage and average crack intensity of a specimen showed that the natural, pre-existing cracks and level of constant stress state dominates the time to reach failure of rock. Further, SEM analysis of thin sections of the shale specimen showed the cracks propagation along the grain boundaries. Finally, we concluded that microscopy is an effective technique for micromechanical analysis of rocks.
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