Methane adsorption amount and kinetics in coal with pre-adsorbed water.

This article focuses on the effects of pre-adsorbed water on methane adsorption quantity and kinetics in coal samples of varying maturities, relevant to coalbed methane (CBM) resource evaluation. Experimental and modeling results show that adsorbed water can reduce methane adsorption by up to 60%, with a more pronounced impact in low-maturity coals, where water forms stronger bonds with oxygen-containing functional groups. Higher-maturity coals exhibit weaker water-coal interactions, leading to less stable adsorbed water that methane can displace more effectively as pressure increases, thereby increasing methane adsorption. Additionally, adsorbed water significantly decreases methane adsorption and mass transfer rates, especially in high-maturity coals, with reductions up to 90% and 80%, respectively. These findings highlight the importance of considering water coverage and coal maturity in assessing methane storage and flow in CBM reservoirs.