沁水盆地中南部太原组煤系页岩孔隙结构特征

Pore structure characteristics of Taiyuan Formation coal measures shale in south central Qinshui Basin

页岩孔隙结构及其控制因素的研究,对页岩气的勘探开发具有重要的指导意义。对沁水盆地太原组海陆过渡相煤系页岩进行了地球化学及低温气体吸附等试验,分析了过渡相页岩的地球化学特征、矿物组成特征和孔隙特征,在此基础上探讨了孔隙发育的控制因素。结果表明,沁水盆地太原组海陆过渡相煤系页岩有机碳质量分数为1.55%~5.21%,平均为3.53%,有机质类型主要为Ⅲ型,且多处于高-过成熟阶段。除少量的长石及碳酸盐矿物外,矿物质组成以质量分数占比55%~69%的黏土矿物和27%~40%的石英为主。黏土矿物中则以高岭石质量分数最高(为23%~65%,平均为48%),其次为伊蒙混层、伊利石和绿泥石。中孔对页岩孔隙体积的贡献最大(贡献率为35.6%~53.7%),其次为大孔(贡献率为25.7%~40.8%)。微孔对孔隙体积的贡献最小,但对比表面积的贡献最大(贡献为72.2%~88.2%),而大孔对比表面积的贡献几乎可以忽略,仅占总比表面积1.5%~2.2%。有机碳含量对微孔及中孔的发育有一定正面影响,但对大孔的影响较小,热演化则不利于孔隙的发育。石英不利于海陆过渡相煤系页岩孔隙的发育,而黏矿物则对孔隙发育有促进作用,尤其是对中孔发育的影响尤为显著,其次是微孔,对大孔影响较弱。黏土矿物中,高岭石和绿泥石有利于页岩孔隙的发育,而伊利石和伊蒙混层则抑制了过渡相页岩孔隙的发育。

The study of the pore structure and its controlling factors of shale reservoir has important guiding significance for further explora⁃tion and exploitation of shale gas.Geochemical and low-temperature gas adsorption experiments were carried out on the transitional coal measures shale of Taiyuan Formation in Qinshui Basin.The geochemical characteristics,mineral macter composition characteristics and pore features were analyzed.On this basis,the controlling factors of pore development were discussed.The results show that the total organ⁃ic carbon(TOC)content of the transitional shale of Taiyuan Formation ranges from 1.55%to 5.21%,with an average of 3.53%,the type of organic matter is mainly type III,and most of them are in a stage of highly to over mature stage.In addition to a small amount of feldspar and carbonate minerals,the two main components of this shale are 55%~69%of clay minerals and 27%~40%of quartz.Among the clay minerals,the content of kaolinite is the highest(ranging from 23%to 65%,with an average of 48%),followed by an illite mixed layer,il⁃lite and chlorite.Mesopores are the major contributor to pore volume(between 35.6%and 53.7%),followed by macropore(between 25.7%and 40.8%).The contribution of micropores to pore volume is the smallest,but the contribution of specific surface area is the largest(between 72.2%and 88.2%),while the contribution of macropores to specific surface area is almost negligible,accounting for only 1.5~2.2%of the total specific surface area.The TOC content has a positive effect on the development of micropores and mesopores,but has little effect on macropores,and thermal evolution is not conducive to the development of pores.Quartz inhibit the development of pores,while the total amount of clay minerals is beneficial to the development of pores,especially to mesopore,followed by micropores and weak effects on macropores.In clay minerals,kaolinite and chlorite are beneficial to the development of shale pores,while the illite mixed layer and Illite inhibit the development of pores in the transitional shale.