Abstract In this study, an NMR fluid typing method was applied to two typical anthracite and high volatile bituminous coals to identify different occurrence states of water (adsorbed and non-adsorbed water), and multiphase methane (adsorbed, porous medium confined, and bulk methane) and investigate the effect of the water occurrence states on methane adsorption capacity. First, results of isothermal adsorption analysis conducted using the NMR method was compared to those from conventional volumetric method to verify the precision of the NMR method. Then the influence of adsorbed water and non-adsorbed water on methane adsorption was examined based on two parallel treatments. For bituminous coal, the adsorbed water remarkably reduced the Langmuir adsorption volume, whereas adding non-adsorbed water had no effect on gas adsorption. In contrast, for anthracite coal, the methane adsorption capacity revealed a downward trend with increase in both adsorbed water and non-adsorbed water. The explanation is that adsorption competition between water molecules and methane gas molecules can constrain further adsorption of methane on the coal matrix. Thus, adsorbed water negatively impacts gas adsorption for both anthracite and bituminous coal. In terms of non-adsorbed water, due to the superior pore conductivity and hydrophilia of bituminous coal, methane gas can easily pass through the pores in the presence of non-adsorbed water, compared to anthracite, where water blocking and the Jamin effect tend to occur. Even water droplets formed because of anthracite’s hydrophobicity can utterly block the pore throats, resulting in a continuous decrease in methane adsorption capacity. The implications of this study are important for better understanding the influence of various occurrence states of water on the adsorption/desorption processes in unconventional reservoirs.

中文翻译：

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水分赋存对煤吸附甲烷能力的影响：烟煤与无烟煤的比较

摘要 本研究将 NMR 流体分型方法应用于两种典型的无烟煤和高挥发分烟煤，以识别不同赋存状态的水（吸附水和非吸附水）和多相甲烷（吸附、多孔介质封闭和块状甲烷）。 ) 并研究水的赋存状态对甲烷吸附能力的影响。首先，将使用 NMR 方法进行的等温吸附分析的结果与常规体积法的结果进行比较，以验证 NMR 方法的精度。然后基于两个平行处理检查吸附水和非吸附水对甲烷吸附的影响。对于烟煤，吸附水显着降低了朗缪尔吸附量，而加入非吸附水对气体吸附没有影响。相比之下，对于无烟煤，随着吸附水和非吸附水的增加，甲烷吸附量呈下降趋势。解释是水分子和甲烷气体分子之间的吸附竞争可以限制甲烷在煤基质上的进一步吸附。因此，吸附水对无烟煤和烟煤的气体吸附产生负面影响。在非吸附水方面，由于烟煤优越的孔隙导电性和亲水性，在非吸附水存在的情况下，甲烷气体很容易通过孔隙，而无烟煤则容易发生堵水和贾敏效应。发生。即使是由于无烟煤的疏水性而形成的水滴也会完全堵塞孔喉，导致甲烷吸附能力不断下降。