Abstract Water is considered ubiquitous within the shale reservoirs and mainly stored in the hydrophilic clay minerals. The water distribution characteristics and its effect on pore structure are important for the gas-in-place of shale systems. In this work, water vapor adsorption on montmorillonite (Mt), kaolinite (Kaol) and illite (Il) were performed to investigate the behaviors of water adsorption on shale clay. Subsequently, the moisture-equilibrated samples were conducted with N2 gas-adsorption techniques to investigate the effect of adsorbed water on pore structure characteristics, such as apparent pore size distribution (APSD), N2 BET specific surface area (N2-BET SSA) and pore volume (PV). The results show that the water uptake isotherms of our samples have the sigmoidal-shaped profiles and GAB model provides a good fit for the adsorption behavior. In addition, The APSD curves under different relative humidity (RH) conditions have validated the condensation effect and indicated that the small pores (approximately smaller than 5 nm) are blocked by the capillary water and will disappear on the APSD curves at RH of 98% while the large nanopores (> 5 nm) are covered with water film, these effects will lead dramatically decrease of N2-BET SSA. Taking Mt and Il samples as the examples, the N2-BET SSA has declined to 33.51% and 33.66% compared with the dry conditions when Sw approaches to 50%. Meanwhile, these effects also indicate that the gas storage for clay minerals is massively overestimating under dry condition, the contribution to methane adsorption might be negligible in the actual shale reservoir.

中文翻译：

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吸水及其对页岩黏土孔隙结构特征的影响

摘要 水在页岩储层中普遍存在，主要储存在亲水性粘土矿物中。水的分布特征及其对孔隙结构的影响对于页岩系统的气藏具有重要意义。在这项工作中，水蒸气吸附在蒙脱石 (Mt)、高岭石 (Kaol) 和伊利石 (Il) 上，以研究水在页岩粘土上的吸附行为。随后，水分平衡的样品用 N2 气体吸附技术进行研究，以研究吸附水对孔隙结构特征的影响，如表观孔径分布 (APSD)、N2 BET 比表面积 (N2-BET SSA) 和孔隙率。体积 (PV)。结果表明，我们样品的吸水等温线具有 S 形曲线，GAB 模型很好地拟合了吸附行为。此外，不同相对湿度（RH）条件下的 APSD 曲线验证了冷凝效果，表明小孔隙（约小于 5 nm）被毛细管水阻塞，在 RH 为 98% 的 APSD 曲线上会消失当大纳米孔（> 5 nm）被水膜覆盖时，这些效应将导致 N2-BET SSA 显着降低。以Mt和II样品为例，当Sw接近50%时，与干燥条件相比，N2-BET SSA分别下降到33.51%和33.66%。同时，这些影响也表明干燥条件下粘土矿物的储气量被大量高估，