The presence of water in coal and its interaction plays pivotal roles in the storage and migration of coalbed methane (CBM), making it imperative to understand the water-occurrence across different coal ranks to guide CBM exploitation effectively. Here, a novel method for categorizing water into condensed and adsorbed forms based on their dehydration dynamics is proposed using differential thermogravimetric curve and the Arrhenius equation, offering a straightforward process and enabling the assessment of the interaction strength between water and coal. The result indicates that the total water capacity decreases initially before subsequently increasing as coal rank increases from 0.28 to 2.33% R_o,max, with the ratio of condensed water exhibiting an S-shaped curve. Remarkably, the condensed water capacity is correlated linearly with the total pore volume. The adsorbed water in low-rank coal is controlled primarily by the level of oxygen functional groups, whereas in medium-high rank coal it is controlled primarily by the specific surface area. Based on this, the controlling equations of water capacity and coal–water structure models were established. Additionally, coal–water interaction strength decreases significantly after the first coalification jump, with the strength of low-rank coal being approximately 2.54 times higher than that of medium-high rank coal. This discrepancy arises from the combined influence of multiple oxygen functional groups in low-rank coal on adsorbed water. This paper enhances the understanding of drainage process in coal reservoirs of varying ranks, which can facilitate the efficient extraction of CBM.

煤中水的存在及其相互作用在煤层气（CBM）的储存和运移中发挥着关键作用，因此必须了解不同煤种的水存在情况以有效指导煤层气开采。在此，提出了一种使用微分热重曲线和阿伦尼乌斯方程根据脱水动力学将水分类为冷凝和吸附形式的新方法，提供了一个简单的过程并能够评估水和煤之间的相互作用强度。结果表明，随着煤阶从0.28%R _o,max 增加到2.33%R _o,max ，总水容量先减小后增加，冷凝水比例呈现S形曲线。值得注意的是，冷凝水容量与总孔体积线性相关。低阶煤中的吸附水主要由氧官能团的水平控制，而中高阶煤中的吸附水主要由比表面积控制。在此基础上，建立了水容量控制方程和煤水结构模型。此外，第一次煤化跳跃后，煤水相互作用强度显着下降，低阶煤的强度比中高阶煤高约2.54倍。这种差异是由低阶煤中多个含氧官能团对吸附水的综合影响引起的。本文增强了对不同级别煤储层排水过程的认识，有利于煤层气的高效开采。