Influence of deep coal-rock heterogeneity on damage evolution path and risk assessment in drilling engineering

Deep coal-rock mining faces complex environments with high in-situ stress and strong heterogeneity, posing severe threats to drilling engineering safety. This study systematically investigated the influence mechanism of heterogeneity on damage evolution paths and its application in drilling risk assessment through multi-scale characterization, laboratory experiments, numerical simulation, and comprehensive evaluation. A quantitative evaluation methodology was established using CT scanning, acoustic testing, SEM, and XRD techniques, incorporating 6 primary and 15 secondary indicators to achieve heterogeneity classification ($$ I_{H} $$=0.24–0.78). The methodology was validated using 14 sampling points from three coalfields (Ordos Basin, Qinshui Basin, and Huainan Mining Area) spanning different coal ranks and tectonic settings. Through 210 triaxial compression tests with synchronous AE monitoring on 168 specimens from 14 sampling points, three mechanisms controlling damage evolution were revealed: stress concentration, crack propagation path alteration, and energy dissipation differentiation. Three typical damage evolution paths were identified: progressive type (characterized by gradual and continuous damage accumulation), step-wise type (featuring intermittent damage jumps at discrete stress levels), and burst type (exhibiting abrupt damage surge near peak stress) ($$ \sigma _{{\text{int} }} /\sigma _{c} = 0.67 - 0.45I_{H} $$, $$ R^{2} = 0.91 $$, n = 42, p < 0.001). A numerical model considering heterogeneity was constructed with high accuracy (error < 5%), and the damage depth prediction equation was established ($$ D_{d} = 0.17e^{{2.68I_{H} }} $$, $$ R^{2} = 0.968 $$, n = 14, p < 0.001), revealing damage depth increases from 0.32 m to 1.18 m (269% increase). A risk assessment framework based on damage evolution paths was developed with tiered management strategies. Field applications across 28 drilling operations in three mining areas achieved 63% reduction in wellbore instability, 45% decrease in drilling fluid loss, and 55% reduction in pipe sticking risk, providing scientific basis for deep coal seam drilling engineering.