A METHOD FOR EXTRACTING 3D FRACTURE GEOMETRIES AND ACQUIRING THEIR MECHANICAL PROPERTIES FROM CT SCANNING IMAGES

摘要

Fractures in rock masses subjected to considerable in situ stress may close, propagate, or coalescence with other weak planes. These responses determine the mechanical properties of the rock and can significantly influence the exploitation of oil and gas resources and the construction of subsurface civil engineering projects. In this paper, based on computed tomography (CT) scanning images, we proposed a method for extracting the three-dimensional (3D) geometries of fractures in rock samples and acquiring the initial fracture stiffness and maximum apertures. In this method, fractures in coal samples were extracted from CT scans by combining Sobel edge detection with a local threshold algorithm and were then reconstructed through superposition. To analyze the mechanical properties of these fractures, the reconstructed fractures were subsequently divided into several fragments simplified as two subparallel plates. The initial fracture stiffness was subjected to the distribution and magnitude of the initial contact areas of a fracture. For a single fracture, if the initial contact areas are larger and more dispersed, the initial fracture stiffness will increase. The permeability values calculated from the reconstructed 3D fractures are consistent with and have the same order of magnitude as those from laboratory experiments. Therefore, this method is effective and can be used to elucidate the entire process of fracture closure and to predict the permeability of rocks.