页岩孔隙中气—水赋存特征研究——以川东南地区下志留统龙马溪组为例

以川东南地区下志留统龙马溪组页岩为研究对象，借助重量法水蒸气吸附仪、重量法甲烷等温吸附仪以及页岩组成和孔隙结构等分析手段，开展束缚水、吸附气赋存定量研究，并探讨了微纳米孔隙中气—水赋存特征及主要影响因素。研究表明，不同类型页岩束缚水赋存能力差异较明显，可以利用水蒸气吸附—脱附和GAB模型比较准确地定量描述束缚水特征。页岩最大单层水分子吸附量与黏土矿物含量呈显著的正相关，表明黏土矿物为水分子提供了主要的活性吸附位。页岩对水分子的吸附能力要整体高于甲烷分子，而甲烷分子则主要以单层吸附形式在孔隙中赋存。不同页岩中束缚水、吸附气和游离气赋存的孔隙空间存在差异。2 nm以下孔隙均被吸附气和孔隙水所占据；有机碳（TOC）含量小于2.5%的页岩中游离气主体赋存空间约为5 nm以上孔隙，而TOC含量大于2.5%的页岩中游离气赋存空间主体约为3 nm以上孔隙；有机碳含量越高，游离气赋存的空间占比越高。 

Co-occurring characteristics of pore gas and water in shales: a case study of the Lower Silurian Longmaxi Formation in the southeastern Sichuan Basin

In this paper, the co-occurring characteristics of pore gas and water in the Longmaxi Formation shales in the Sichuan Basin, South China were investigated. Water vapor and methane adsorption by the means of gravimetric methods were carried out to quantitatively determine the behavior of gas and bounding water in micro-nano pores. The impact of the shale compositions and pore structures on the occurring characteristics were discussed. Results showed that the storage capacity of bound water in different types of shales varied dramatically, and the characteristics of bound water could be described by the water vapor adsorption curve and the GAB model. There is an apaprent positive correlation between the maximum monolayer water molecule adsorption capacity and the clay mineral content in shales, indicating that clay minerals provide the main active adsorption sites for water molecules. The adsorption capacity of shale to water molecule is higher than that of methane molecule overall, and methane molecule mainly exist in pores with the form of monolayer adsorption. Bound water, adsorbed gas and free gas could be stored in different pore ranges of different shales. Pores with diameters lower than 2 nm are occupied by bounding water and adsorbed gas. For shales with TOC<2.5%, free gas would be stored in pores with diameters larger than 5 nm approximately, while for the shales with TOC>2.5%, free gas would be stored in pores with diameters larger than 3 nm approximately. The higher the TOC content, the higher the proportion of the free-gas storage space.