Abstract:

Shale gas, an emerging unconventional natural gas mainly composed of methane (CH₄), is of great significance to optimize China’s current energy consumption structure and to mitigate environmental pollution issues during energy consumption. Previous study has shown that shale gas in gas shale reservoirs mainly exists in adsorbed state. The adsorption performance of gas shales depends on both physicochemical properties of shales and external reservoir conditions. Among them, the moisture contained in shales significantly affects the adsorption/desorption of shale gas. Therefore, based on literature review, this work analyzed the occurrence and distribution of moisture in gas shales, summarized the analysis method of moisture in shale reservoirs, and pointed out the research trend regarding moisture occurrence and distribution. The results showed that the moisture in gas shales mainly existed in pore structures, and the moisture contained in inorganic pores was higher than that of organic pores; the water molecules were mainly adsorbed to the hydrophilic sites of the organic pores through hydrogen bonds, and the hydrogen bonds and surface forces combined with clay particles or pore surface; the moisture content was related to both clay mineral content and TOC content of gas shales; hitherto, the experimental methods for determining the occurrence and distribution of water molecules in shales comprised water vapor isothermal adsorption, low temperature difference scanning calorimetry, low field nuclear magnetic resonance, infrared thermal imaging, and low-temperature plasma ashing. Although study on moisture in gas shales had gained broad attention, it was still insufficiently compared with that on moisture in coals. Thus, the following aspects need to be further concentrated on. To start with, it was necessary to determine content distribution and spatial distribution characteristics of moisture in inorganic minerals and organic matter, furthermore, to examine water dependence of CH₄ adsorption/desorption within shales, and finally, to address the mechanism of water dependence of CH₄ adsorption/desorption in shales using experiment and simulation approach.

Key words: gas shales, moisture, occurrence, shale gas, adsorption/desorption

摘要：

页岩气（主要组分为甲烷，CH₄）作为一种新兴的非常规天然气，对于优化我国现行能源消费结构、缓解能源消耗过程中的环境污染问题具有重要意义。研究表明，含气页岩储层中页岩气主要以吸附态形式存在。影响含气页岩吸附性能的因素包括页岩自身理化性质和外部储层条件。其中，页岩中的水分是影响页岩气吸附/解吸的重要因素。因此，本文结合国内外相关研究工作，分析了含气页岩中水分的赋存与分布特征，归纳了页岩储层中水分的分析方法，指出了水分赋存与分布的后续研究方向。分析表明：①页岩中水分主要赋存于孔隙结构中，且无机孔隙中的水分赋存量比有机孔隙多；②水分子主要通过氢键吸附于有机孔隙的亲水性位点，以及经由氢键和表面作用力结合于黏土颗粒或孔隙表面；③水分含量与页岩黏土矿物含量及总有机碳（TOC）含量有关；④探明页岩中水分赋存与分布的实验表征手段包括水蒸气等温吸附、低温差示扫描量热、低场核磁共振、红外热成像和等离子体低温灰化等。虽然页岩中水分的研究已经引起国内外学者的关注，但是相比煤中水分的研究仍显不足。因此，本文指出后续需开展以下工作：探明水分在页岩中的无机矿物质空间和有机质空间的含量分布和空间分布特征；明确水分对页岩吸附/解吸CH₄流体的作用规律；联用实验科学和理论模拟方法，探明水分对页岩吸附/解吸CH₄流体的作用机理。

关键词: 含气页岩, 水, 赋存, 页岩气, 吸附（作用）/解吸