Seepage Evolution Law of Coal during Loading Process Based on Digital Core

Abstract

Coal seam water injection is a widely employed strategy to mitigate dust in coal mines, and the effectiveness of water injection is intricately linked to the internal pore and fracture structure of the coal. During the process of coal mining, the stress induced by mining activities has a significant impact on the pore and fracture structure of the coal mass surrounding the borehole, consequently altering its seepage characteristics. In order to investigate the seepage evolution patterns of coal seams, this study was based on in situ micro-computed tomography (CT) imaging tests to extract the interconnected fracture models of a coal sample under various axial force loading conditions. Subsequently, a numerical simulation was conducted to simulate water injection seepage and analyze the permeability evolution of coal. According to the obtained results, when the axial force was loaded from 431 N to 732 N, the interconnected fractures inside the coal increased, and the seepage velocity and mass flow rate increased slightly. When the axial force was loaded to 1,100 N, the interconnected fractures experienced a further increase in number, leading to the formation of a complicated interconnected fracture network. Therefore, the resistance of water in seepage increased, resulting in a slight decrease in seepage velocity, but a significant increase in mass flow rate. When the axial force reached 492 N after the peak load, a stable interconnected fracture network was formed in the coal, the fracture development became slow, and the seepage rate as well as the mass flow rate reached a relatively stable state. Under the influence of axial force loading, the fracture structure within coal exhibits significant development, leading to a notable enhancement in its seepage characteristics. The research findings presented in this paper hold significant practical implications for the utilization of mining-induced stress in guiding the design of parameters for coal seam water injection and its subsequent field application.