Abstract The variation in pore water distribution within gas shale reservoirs has a significant effect on gas content, and thus on resource evaluation. However, the characteristics of water micro-distribution and its effects on pore parameters are still not well understood due to the mixed wettability of shale and the complexity of the pore structure. In this study, six lower Permian transitional shale samples from the southern North China Basin, humidified at four levels up to a relative humidity of 98%, were selected for moisture-equilibrated experiments and low-pressure N2 gas adsorption measurements. The results indicate that the adsorbed moisture in transitional clay-rich shales can be divided into capillary condensation water in the micropores and monolayer–multilayer adsorbed water in the non-micropores. Moreover, thermal maturity (VRo), total organic carbon, clay, and carbonate are positively correlated with the adsorbed moisture and micro-/mesopores, indicating that water in shales could be hosted in inorganic pores as well as in organic pores. Furthermore, the distribution of adsorbed moisture is mainly controlled by the VRo, component wettability (i.e., organic matter, clay, pyrite, and carbonate), and pore structure (micro-/mesopore distribution). In addition, a subtle adsorbed moisture may significantly reduce both the pore volume (PV) and specific surface area (SSA) of micropores, and the effect on micropores and SSA is more pronounced than that on the respective non-micropores and PVs. Additionally, the mechanism of clay swelling and pore expansion in clayey shale can provide certain insights for water–methane competitive adsorption, identifying clay type and pore size, and the formation of organo-mineral complexes.

中文翻译：

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吸附水分对海陆过渡页岩孔径分布的影响：来自岩相差异和粘土膨胀的洞察

摘要 含气页岩储层孔隙水分布的变化对含气量有显着影响，进而影响资源评价。然而，由于页岩的混合润湿性和孔隙结构的复杂性，水的微观分布特征及其对孔隙参数的影响仍不清楚。在这项研究中，选择了来自华北盆地南部的六个下二叠纪过渡页岩样品，在四个级别加湿至相对湿度为 98%，用于水分平衡实验和低压 N2 气体吸附测量。结果表明，过渡性富粘土页岩的吸附水分可分为微孔内的毛细管凝结水和非微孔内的单层-多层吸附水。此外，热成熟度（VRo），总有机碳、粘土和碳酸盐与吸附水分和微孔/介孔呈正相关，表明页岩中的水既可以存在于无机孔中，也可以存在于有机孔中。此外，吸附水分的分布主要受 VRo、组分润湿性（即有机质、粘土、黄铁矿和碳酸盐）和孔隙结构（微/中孔分布）控制。此外，细微的吸附水分可能会显着降低微孔的孔体积（PV）和比表面积（SSA），并且对微孔和 SSA 的影响比对各自的非微孔和 PV 的影响更明显。此外，粘土质页岩中粘土膨胀和孔隙膨胀的机制可以为水-甲烷竞争吸附、识别粘土类型和孔径提供一定的见解，