Dynamic Transport and Occurrence of Hydrogen in Methane-Bearing Coal Seams: Implications for Geological Hydrogen Preservation

Coal seams are increasingly recognized as important components of subsurface hydrogen systems， yet the occurrence state and preservation potential of hydrogen in methane-bearing coal remain poorly constrained. In particular， competitive interactions between hydrogen (H₂) and methane (CH₄) may fundamentally control hydrogen retention and loss in coal-bearing strata. In this study， blank-corrected multicomponent breakthrough experiments combined with Monte Carlo simulations were conducted to investigate the dynamic competitive behavior of H₂ and CH₄ in a low-rank coal from Inner Mongolia under methane-rich conditions (CH₄:H₂ = 3:1). Breakthrough results reveal a pronounced contrast between the two gases: methane exhibits delayed breakthrough and a broader mass transfer zone， indicating strong affinity to the coal matrix， whereas hydrogen shows a rapid breakthrough. Quantitative analysis shows that CH₄ uptake (9.478 ml·g^-1) is approximately five times higher than that of H₂ (1.877 ml·g^-1) under competitive conditions at 25 ℃， and methane reduces the effective hydrogen retention by approximately 14.7% under the studied conditions. Monte Carlo simulations further indicate that moisture amplifies this selectivity by preferentially reducing hydrogen adsorption. These results suggest limited hydrogen retention potential in methane-bearing coal seams under methane-rich conditions， particularly in the adsorbed state. This study provides geological insights into hydrogen occurrence and preservation in coal-bearing systems， with implications for natural hydrogen resource evaluation in methane-rich basins.