鄂西黄陵背斜南翼下寒武统水井沱组页岩孔隙结构与吸附能力

Pore structure and adsorption capacity of shale in the Lower Cambrian Shuijingtuo Formation in the southern flank of Huangling anticline,western Hubei

以鄂西黄陵背斜南翼秭地2井下寒武统水井沱组海相富有机质页岩为研究对象,在水井沱组一段和二段选取代表性页岩样品,利用CO2和N2物理吸附、高压压汞、氩离子抛光-场发射扫描电镜(FE-SEM)等多尺度孔隙结构测试技术和观察手段以及有机质孔统计分析方法,结合甲烷等温吸附实验以及其他测试手段,描述了页岩地球化学、矿物组成和岩相特征,研究了页岩孔隙类型、孔隙形态、孔径分布和比表面积等孔隙结构参数,分析了页岩甲烷吸附能力,讨论了页岩孔隙发育和孔隙结构的影响因素。研究表明:秭地2井水井沱组一段和二段富有机质黑色页岩成熟度Ro约为2.5%,页岩岩相主要有硅质页岩、混合质页岩和黏土质页岩;页岩有机质孔隙形状多样、边界不规则,孔径偏小,大多孔径<50nm;无机质孔/缝丰富,成因类型多,孔隙形状多变;页岩微孔(孔径为0.3~2.0nm)中的有机质微孔十分发育,孔径在2~5nm介孔中的有机质介孔占有较大比例;孔径>5nm的介孔+宏孔中的无机质孔隙占优势;页岩比表面积大、对甲烷的吸附能力强;硅质页岩的孔隙结构和吸附能力相对较好;页岩有机碳含量、碳酸盐矿物和黏土矿物含量以及页岩岩相等因素对页岩孔隙发育和孔隙结构有重要影响。

Aiming at the marine organic-rich shale in the Lower Cambrian Shuijingtuo Formation in the Well Zidi2 in the southern flank of the Huangling anticline in western Hubei,this study selects shale samples from the first and second members of Shuijingtuo Formation.Using the multi-scale testing techniques such as CO2 and N2 physical absorption,high-pressure mercury injection,and argon ion polishing-field emission scanning electron microscope(FE-SEM)the observation methods for pore structure and the statistical analysis methods of organic pores in combination with methane isothermal adsorption experiments and other basic testing methods,this paper describes the geochemistry,mineral composition and lithofacies characteristics of shale,investigates the pore type,pore shape,pore size distribution and specific surface area of shale and other pore structure parameters,analyzes the methane adsorption capacity of shale,and explores the factors affecting the pore development and pore structure of shale.The research results show that Roof the organic-rich black shale in the first and second members of Shuijingtuo Formation in the Well Zidi2 is about 2.5%,and the shale lithofacies are mainly siliceous shale,migmatitic shale,and clayey shale;organic pores of shale have various shapes,irregular boundaries,and small pore sizes,most of which have a pore diameter of less than50 nm.Inorganic pores/seams are abundant,with various types of geneses and variable shapes micropores in shale(pore size of 0.3-2.0 nm)develops well,and organic mesopores occupy a large proportion in mesopores with the pore size of 2-5 nm;inorganic pores are dominant in mesopores with a pore size>5 nm and macropores.Shale has a large specific surface area and strong methane adsorption capacity;the pore structure and adsorption capacity of siliceous shale are even better.The organic carbon content,carbonate mineral and clay mineral content of shale,shale lithofacies and other factors have important effects on the pore development and pore structure of shale.