江汉盆地潜江凹陷盐间潜3^4油组储层微观结构特征及与物性的关系

Micro-pore structure in an inter-salt shale oil reservoir and the relationship with physical properties in the fourth section of the third member of Qianjiang Formation,Qianjiang Sag,Jianghan Basin

以X衍射、薄片、常规扫描电镜及氩离子抛光扫描电镜、FIB三维孔隙重构等手段,结合压汞及氮气吸附孔体积定量分析,研究了江汉盆地潜江凹陷盐间潜3~4油组页岩油储层微观结构及与物性的关系。按矿物含量的高低,把储层划分为云质泥岩、泥质云岩及含泥云岩三大类。该储层矿物组成、结构非均质性强,常规柱孔隙度变化大,在1%~13%之间。其中云质泥岩孔隙度低,泥质云岩、含泥云岩孔隙度高,钙芒硝含量高的泥岩孔隙度较低。储层微观结构变化大,云质泥岩具定向排列结构,以狭长状或扁平状微孔隙为主;孔径小,以直径20~50 nm的孔隙体积为主,最大连通喉道小,在22~42 nm之间。泥质云岩以残余粒间孔及粒间充填的黏土片间孔为主,孔径变大,以直径20~80 nm的孔隙体积为主,最大连通喉道变化大,在16~158 nm之间。含泥云岩以均匀晶粒结构、多边形等轴状晶间微孔为主;孔径大,以直径80~180 nm的孔隙体积为主,最大连通喉道大,在158~196 nm。云质泥岩、泥质云岩、含泥云岩的孔隙连通分别具有"缝—缝、孔—缝、孔—孔相连"的特征,含泥云岩孔隙度大、连通喉道宽、孔隙结构优,具最好的页岩油储集空间。

The micro-pore structure of an inter-salt shale oil reservoir and its relationship with physical properties in the fourth section of the third member of Qianjiang Formation(Eq43)in the Qianjiang Sag of Jianghan Basin were studied using X-ray diffraction,thin section observation,conventional scanning electron microscopy(SEM),argon ion polishing SEM and three-dimensional pore reconstruction of focused ion beam,microscopy combined with quantitative analysis of mercury intrusion and nitrogen adsorption pore volume.According to the level of mineral content,the reservoir is divided into three categories:dolomitic mudstone,argillaceous dolomite and muddy dolomite.The mineral composition and structure of the reservoir are highly heterogeneous,and the conventional core-plug porosity varies greatly,ranging from 1%to 13%.The porosity of dolomitic mudstone is low,the porosity of argillaceous dolomite and muddy dolomite is high,and the porosity of mudstone with high content of glauberite is low.The reservoir microstructure changes greatly,and the dolomitic mudstone has a directional arrangement structure,mainly with elongated or flat micropores.The pore size is small,with a pore diameter of 20-50 nm,and the largest connecting throat is small,ranging from 22 to 42 nm.The argillaceous dolomite mainly contains residual intergranular pores and pores between clay layers.The pore diameter becomes larger,mainly 20 to 80 nm.The maximum connecting throat varies greatly,between 16 and 158 nm.The muddy dolomite is mainly composed of uniform grain structure,polygonal equidimensional intergranular micropores.The pore size is large,80-180 nm.The largest connecting throat is large,at 158-196 nm.The pore connection of dolomitic mudstone,argillaceous dolomite and muddy dolomite has the characteristics of"fracture-fracture,pore-fracture,pore-pore connection",respectively.The muddy dolomite has high porosity,wide connecting throats,and favorable pore structure,indicating the best shale oil storage space.