Investigation on capturing bedding planes in laminated shale through advanced physics-informed image processing for multiscale geomechanical simulation

Abstract

Shale is characterized by its laminated and fissile nature, consisting of numerous thin layers that easily split along bedding planes. Traditional geomechanical simulations often simplify shale's complex structure by representing bedding planes as continuous and equidistant. While this approach is numerically efficient and useful for approximating general shale behavior, it limits our understanding of the shale's true mechanical response to mining-induced stress. This study proposes an advanced physics-informed image processing method to capture bedding planes across different orientations, scales, and shale types. The method includes five procedures: 1) projection transfer, where a 3D cylinder is projected onto a 2D image; 2) edge detection, where physics-informed edges are detected to obtain bedding plane pixels; 3) clustering, where bedding plane pixels are clustered to form bedding plane lines; 4) representation of bedding planes; and 5) feature extraction of bedding planes. Our method effectively captures bedding planes across different orientations (0°, 45°, and 90°), scales (interim bedding planes at the laboratory scale and ordinary bedding planes at the rock mass scale), and shale types (Opalinus shale, sandy shale, gray shale, black shale, and carbonaceous shale). The geometric information extracted from the bedding planes—including coordinates, number, spacing, length, and distribution characteristics—has been summarized into a comprehensive database for different shales at different scales. The results show that: at the laboratory scale, the captured interim bedding planes are neither continuous nor equidistant. Their lengths follow a log-normal distribution, with the mean length (LN) ranging from 1.227 to 1.823 and the standard deviation (LN) varying between 1.069 and 5.062. The fitting statistical parameters, including the mean and standard deviation of this distribution, have been summarized. At the rock mass scale, the ordinary bedding planes are continuous but not equidistant. Successful multiscale geomechanical simulations in UDEC and FLAC3D were conducted to model uniaxial compression tests at the laboratory scale and shale roof failure at the entry scale, calibrated using laboratory and field observations.