Research on radial stress distribution and gas seepage characteristics of the coal body around boreholes

Addressing the complex issues of elastic–plastic deformation in the coal body around boreholes (CBAB) and gas seepage during gas extraction, this study quantitatively reveals the radial stress distribution characteristics of CBAB based on Mohr–Coulomb strength criteria through post-drilling stress analysis of the surrounding coal body. Radial seepage experiments were simulated, and combined with experimental results, the gas seepage characteristics of CBAB were systematically analysed, validating the permeability evolution model. The findings indicate that CBAB radially divides into a decompression zone, a stress concentration zone and a native rock stress zone. Vertical stress first peaks and then decays, while horizontal stress continuously decreases. Radial segmented permeability experiments demonstrate that CBAB permeability initially drops sharply owing to pore compaction and then undergoes a gradual change dominated by microfractures, eventually stabilizing under rigid matrix control. The calculated results of the CBAB radial permeability evolution model exhibit an R² > 0.95 correlation with experimental flow data.