The study on physical properties and pore seepage characteristics of complex-structured coal seam in Baode Coal Mine

In response to the challenges of gas drainage in the complex-structured coal seams of the Bode Coal Mine, this study conducts field observations and sampling, combined with laboratory experiments, and utilizes multiple experimental methods such as macroscopic characterization of coal-rock hand specimens, industrial analysis, microscopic component analysis, XRD testing, low-temperature liquid nitrogen adsorption, low-field nuclear magnetic resonance （NMR）, and industrial CT scanning. These methods are employed to comprehensively characterize the physical properties and fluid flow characteristics of the coal-rock. The results indicates that the No.8 coal seam exhibits typical complex structural features, with an average of 5-8 intercalated shale layers, and up to 11 layers in some areas. The coal structure is primarily composed of primary structural coal, with relatively low development of tectonic fractures and intrinsic fractures. Microscopic component analysis reveals that the average content of vitrinite is 28.88%, and the average content of clay minerals is 24.53%, with kaolinite being the predominant clay mineral component. In terms of pore structure characteristics, the coal samples are dominated by small pores, followed by medium pores, with fewer micro-pores, and pore sizes are primarily distributed in the range of 0.01-0.6 μm, with the largest proportion in the 0.025-0.10 μm interval. The average porosity of the coal-rock is 5.75%. The connectivity of pores and fractures in the coal-rock is relatively poor, resulting in low permeability of the coal seam and weak fluid flow capacity. Based on these findings, it is recommended to implement large-scale hydraulic fracturing technology in the No.8 coal seam to enhance fragmentation of the coal seam and dense intercalated shale layers, thereby increasing permeability, accelerating gas desorption and seepage, and improving gas drainage efficiency. The research findings provide experimental data and theoretical support for addressing gas drainage challenges at the Bode Coal Mine.