Inhibition mechanisms of gas desorption and pressure inversion in water-bearing coal under stepwise decompression via volume expansion

The interference of moisture in water-bearing coal seams on gas desorption is a key bottleneck restricting the accurate determination of in-situ pressure. In this study, we systematically elucidate the dual inhibition mechanisms of moisture on gas desorption through stepwise volume expansion experiments (moisture content gradient 0-5.11%) combined with multi-scale characterization techniques including low-field nuclear magnetic resonance, scanning electron microscopy, and mercury intrusion porosimetry. Two dominant mechanisms are identified: (1) Competitive adsorption, where moisture occupies mesopore surfaces (2–50 nm, dominant pore size 2.2–4.8 nm), leading to a 28.6% reduction in the Langmuir volume (a); (2) Pore throat blockage—capillary liquid bridges form within ink-bottle pores, hindering gas diffusion. Based on these mechanisms, a modified Langmuir model incorporating an adsorption attenuation coefficient (λ) is proposed, and a dual-mode pressure hierarchical/chained inversion algorithm is developed. The hierarchical method achieves a single-stage pressure inversion error < 1.65%, and the chained method shows a full-process inversion error of only 0.59% at a moisture content of 4.85%. The study indicates that the solidification effect of moisture on the pore system can enhance the predictability of pressure evolution. This method provides a theoretical framework for gas disaster prevention and control in water-bearing coal seams and contributes to improved accuracy in in-situ pressure determination.