Evaluation of rock anisotropy using 3D X-ray computed tomography

The anisotropic nature of fabric and internal structures plays a significant role in fluid flow, heat transfer, and geomechanical behavior in rock. The existence and orientation of anisotropy in various rocks have been evaluated using laboratory experiments and image analyses to characterize anisotropic pore networks, micro-fractures, mineralogy, grain fabric, and stiffness from micro- to macro-scales. We present an assessment of anisotropy in rock by systematic and planar clustering of three-dimensional X-ray attenuation values and associated statistical analysis on the basis that X-ray CT numbers directly represent the internal density of the mineral fabric in the rock mass. Variation in voxel values across the slicing plane for a given orientation enables identification of the unique orientation of anisotropy in rock. The proposed concept is validated using a 3D virtual structure and is applied to four different rock types. The sensitivity of anisotropic features and the image noise effect are further explored to highlight the robustness of the proposed method for evaluating the anisotropy of rock fabrics.