Quantitative characterization of cracking process in oil shale using micro-CT imaging

Our understanding of progressive cracking in rock materials is very important for prediction of failure in rock engineering. Gathering three-dimensional observation of damage evolution process in rock materials has been a challenge. In this article, we realized imaging of cracking in oil shale during uniaxial compressive test using X-ray micro-computed tomography (CT) technology with a resolution of 11.27 μm. We also had fully resolved sequences of micro-cracks damage and cracks growth at different positions and stress levels. The results indicated that the micro cracks initiated at the boundary of specimens, and suffered continuous development during the process including branching, coalescence, and failure. The unstable propagation stage of cracks was assumed to be very close to the peak strength. Continuous loading enlarged the width of the cracks in the failed specimen. However, few new cracks were generated. Besides, several parameters such as the crack length (CL) and fracture network volume (FNV) were selected to quantitatively describe the cracking and damage evolution process. The cracking process, especially the propagation and formation of fracture network, can be precisely characterized these parameters. Our observations provide a powerful methodology for characterizing the dynamic changes in oil shale by fracturing treatment for the improvement and optimization of hydrocarbon recovery.