应用氩离子抛光－扫描电镜方法研究四川九老洞组页岩微观孔隙特征

摘要

Microscopic pore structure is the key to studying shale gas reservoirs.Traditional Scanning Electron Microscope cannot be used to identify topographic irregularities caused by differential hardness of components during mechanical polishing.Microscopic pore structures of Jiulaodong formation shale in the Weiyuan area of the Sichuan basin were investigated using scanning electron microscope coupled with an Ar-ion milling technique.Three types of pores were identified:(1 )mineral matrix pores (pore diameters are mostly 100 -500 nm),mainly including interparticle pores and intraplatelet pores within clay aggregates,and intercrystalline pores within pyrite /anatase and biological pores;(2 )organic matter pores (pore diameters range from tens of nanometers to several micrometers),either controlled by thermal evolution of kerogen or clay minerals coated by organic matter;(3)micro fractures (with length of dozens of micrometers and width of a few micrometers),including shrinkage fracture,tectonic fracture,overpressure fracture and artificial fracture.In conclusion,micro-nano pores in Jiulaodong shale are mainly composed of mineral matrix pores and micro fractures which provide the main storage space and flow channel for shale gas.%微观孔隙结构是页岩储层研究的重点，而扫描电镜方法无法识别机械抛光中由于页岩硬度差异所造成的不规则形貌。本文利用氩离子抛光－扫描电镜方法对四川威远区块九老洞组页岩进行研究，发现了三种孔隙类型：①无机孔以粒间孔和黏土矿物层间孔为主，同时发育晶间孔和生物孔，孔径主体100～500 nm；②有机孔受控于热成熟度或有机黏土复合体，孔径范围数十纳米至数微米；③微裂缝包括成岩收缩裂缝、高压碎裂缝、构造裂缝和人为裂缝，缝宽数微米，缝长数微米至数十微米。研究表明无机孔和微裂缝是九老洞组页岩气的主要储集空间。