富有机质页岩成分与孔隙结构对吸附气赋存的控制作用

The dual influence of shale composition and pore size on adsorption gas storage mechanism of organic-rich shale

富有机质页岩中天然气主要以游离气和吸附气2种形式存在,吸附气占重要比例,可达20%~80%,吸附气的赋存机理复杂,对勘探方法和开采方式有重要影响,通过对我国海相、陆相页岩等温吸附特征与孔隙发育特征进行研究,探讨了页岩成分与孔隙结构对吸附气赋存特征的双重影响。认为：①页岩孔隙结构与页岩成分共同控制吸附气赋存特征。页岩孔隙结构及其表面性质是直接因素,页岩成分如有机碳含量、有机质类型、含水量和成熟度等因素通过影响页岩孔隙结构间接影响吸附气含量;②页岩中吸附气赋存于有机质的微孔、介孔（〈50nm）,储层中黏土矿物吸附性较弱,游离气赋存于矿物宏孔（〉50nm）;③随着成熟度的增高,页岩有机质微孔、介孔孔隙增多,比表面增大,吸附能力增强。当页岩演化至高过成熟阶段,孔隙增大,微孔减少,比表面降低,吸附气含量降低。我国海相页岩成熟度普遍较高,要对吸附气下降界限深入研究。

Shale gas is generally believed to have been stored in forms of free compressed gas and adsorbed gas.The proportion of adsorption gas ranges between 20% and 80%.The storage mechanism of adsorption gas is so complex that it has a great influence on the way of shale gas exploration and development.Based on the comprehensive observation of pore structure and isotherm adsorption of typical marine and terrestrial shale,the dual influencing of shale composition and pore size on gas storage mechanism of organic-rich shale are recognized：（1）The adsorption capacity is controlled by shale composition and pore structure.The pore structure is the direct influencing factor,and the shale maturity and composition,such as TOC content,kerogen type and moisture content,are indirect factors,which can influence the adsorption capacity by the pore structure;（2）The macro-pores（〉50nm）are developed mostly in inorganic mineral,where free gas is stored,and micro-and meso-pores（〈50nm）are developed mostly in organic matters,where adsorption gas is stored;（3）With the increase of thermal maturity,pore abundance and specific surface area in shale become higher,so does the adsorption capacity.However,the adsorption capacity decreases due to the specific surface area decline during the post mature stage.The maturity of marine shale in China is at a high or post mature stage,so the threshold of adsorption decrease needs to be further studied.