宁武盆地山西组过渡相页岩孔隙特征及影响因素

摘要

In order to study the pore characteristics and influence factors of transitional facies shale in Shanxi Formation of Ningwu basin,the shale in Shanxi Formation was systematically sampled to carry out the SEM analysis,low temperature nitrogen adsorption experiment,TOC content test,maturity(Rmax) test,the whole rock mineral X diffraction analysis and porosity test,then the pore types,pore characteristics and influencing factors are discussed.The results show that pores in transitional shale of Shanxi Formation mainly consist of intergranular pores,intercrystalline pores,organic matter pores,organic matter primary pores and dissolution pores and fractures.The pore radius is primarily between 2 nm to 50 nm,and the shapes of the pores inclue open-wedge pores,parallel-plate pores,conical tube pores,ink bottle pores,etc.The average porosity of the shale is 3.64％,the average pore radius is 7.78 nm,the average BET surface area is 11.70 m2/g,and the average total pore volume is 0.0222 cm3/g,indicating a strong storage and adsorption.The shale pores have obvious fractal characteristics,and the fractal dimension is 2.61～2.77,which is positively correlated with the percentage of micropore volume;the shale pore development is influenced by TOC content,maturity(Rmax)and mineral composition.%为了研究宁武盆地山西组过渡相页岩的孔隙特征和影响因素,对宁武盆地山西组过渡相页岩进行了系统采样,并针对性地进行了扫描电镜分析、低温氮吸附实验、TOC含量测试、有机质成熟度(Rmax)测试、全岩矿物X衍射分析和孔隙度测试,探讨了页岩孔隙类型、孔隙特征及影响因素.结果表明:研究区页岩孔隙类型主要以粒间孔、晶间孔、有机质气孔、有机质原生孔、溶蚀孔及裂缝为主,大小以2～50 nm的介孔为主,孔隙形态包括开放的尖壁形孔、平行壁孔、锥型管状孔、墨水瓶孔等;页岩平均孔隙度为3.64％,平均孔径为7.78 nm,BET比表面积平均为11.70m2/g,总孔体积平均为0.022 2 cm3/g,具有较强的储集性和吸附性;页岩孔隙具有分形特征,分形维数为2.61～2.77,分形维数与微孔体积分数表现出良好的正相关性;页岩孔隙发育受TOC含量、成熟度(Rmax)和矿物组成的影响.