鄂尔多斯盆地渭北地区页岩纳米孔隙发育特征及其控制因素

为深入研究鄂尔多斯盆地东南缘渭北地区页岩储层中纳米孔隙的发育特征及其地质控制因素，对采自太原组、山西组和延长组三套泥页岩层的11块样品进行低温氮吸附实验、氩离子抛光-场发射扫描电镜、显微组分、镜质体反射率（R_o）、总有机碳（TOC）和X-射线衍射等系列分析测试。研究结果表明，研究区泥页岩处于低成熟向成熟转变阶段，有机碳含量差异较大，储层纳米级孔隙以中小孔（粒径2~50 nm）为主，约占总孔体积的63.5%，BET比表面积大多在10 m²/g以上，有利于页岩气的吸附；孔隙形态以“狭缝状”和“墨水瓶”形孔隙为主。研究区页岩的矿物类型具有明显的区域差异性：韩城区以粘土矿物为主，而铜川区以脆性矿物为主。粘土矿物含量与微孔（粒径<2 nm）、中小孔总含量呈显著的正相关性，而脆性矿物含量与大孔（粒径>50 nm）含量正相关，因此矿物类型差异是影响该区页岩纳米孔隙发育的主控因素。另外，R_o与TOC对纳米孔隙发育也有一定的影响：页岩R_o越高，大孔含量越高、中小孔含量越低；有机碳含量越高，微孔和中小孔含量越高。

Characteristics and controlling factors of nanopores in shales in Weibei,Ordos Basin

To better understand the development characteristic of nanopores and its geological controlling factors,we collected 11 shale samples from the Taiyuan,Shanxi,and Yanchang formations in the Weibei,southeastern Ordos Basin,and performed low-temperature nitrogen adsorption,Argon-ion milled and field emission scanning electron microscopy(FE-SEM),vitrinite reflectivity(R_o)and maceral composition,total organic carbon(TOC)content and X-ray diffraction(XRD)analyses.The selected shale samples are in the transition period from low mature to mature,and are quite different in TOC.The nanopores in the shales are dominated by pores within the size of 2~50 nm,which account for 63.5% of the total pore volume.The BET specific surface area is commonly higher than 10 m²/g,indicating a favorable condition for methane adsorption.The pore types are mainly of narrow-slit pores and ink-bottle shaped pores.The dominant mineral compositions are different from area to area:clay minerals being dominated in the Hancheng area,while brittle minerals being dominated in the Tongchuan area.Clay mineral content is positively correlated with the total content of nanopores smaller than 2 nm and that within 2-50 nm,while the brittle mineral content is positively correlated with the content of nanopores larger than 50 nm.This means that the difference in mineral types is the main control factor on the development of nanopores.Moreover,R_o and TOC also have some influences on the development of nanopores.The higher the R_o is,the higher content of large nanopores is,but the lower content of medium to small nanopores is.In addition,the higher the TOC,the higher content of medium to small nanopores is.