Fracture dynamic evolution features of a coal-containing gas based on gray level co-occurrence matrix and industrial CT scanning

The expansion evolution law of internal fractures of coal under external load is of great significance to coalbed methane production and to control coal and gas outburst disasters. The coal body is in a three-dimensional (3D) stress state under the action of original in-situ stress. It is necessary to study the fracture evolution law of a loaded coal-containing gas under triaxial compression. The industrial computed tomographic (CT) scanning test of a loaded coal-containing gas under triaxial loading was carried out using the industrial micro-CT scanning system for the loaded coal-containing gas. The CT images and stress–strain curves of coal samples were obtained at each deformation stage. The 3D digital reconstruction of CT scanning data was carried out using image analysis software. Next, 3D visualization and quantitative characterization of coal sample internal fractures were realized. Based on the gray level co-occurrence matrix (GLCM) theory, the fracture dynamic expansion characteristics and laws of the loaded coal-containing gas were analyzed. The results show that the existence of gas pressure weakens the mechanical properties of the loaded coal-containing gas and accelerates the expansion of cracks. The two-dimensional fractures of the loaded coal-containing gas first close and then expand, and then expand rapidly after the peak, forming a connected two-dimensional fracture network. The 3D fracture volume and fracture density first show a decreasing and then an increasing trend, which can be divided into three stages: fracture compaction and closure, new fracture initiation and expansion, and main fracture accelerated expansion and penetration. In the GLCM analysis, the contrast first decreases and then increases, the energy and homogeneity first increase and then decrease, and the correlation presents a monotonic decreasing trend. The analysis results accurately describe the overall development law of the internal cracks of the loaded coal-containing gas changing with stress increase.