基于扫描电镜大视域拼接技术定量表征致密储层微观非均质性

Quantitative characterization of micro heterogeneity of tight reservoirs by large-view FE-SEM splicing technology

高分辨率扫描电镜技术是研究致密储层非均质性最直观的方法,但存在视域代表性的问题。以南襄盆地泌阳凹陷古近系核桃园组三段致密储层为例,基于扫描电镜大视域拼接技术,定量揭示了不同类型致密储层的微观非均质性。结果表明,研究区致密砂岩储集空间类型以粒间孔和粒内孔为主,同时发育少量微裂缝;泥页岩储集空间类型同样以粒间孔和粒内孔为主,有机孔和微裂缝相对较少。通过场发射扫描电镜大视域拼接技术与统计学方法结合,探讨了泥岩、页岩、泥质粉砂岩、砂岩等致密储层的矿物微观非均质性和孔隙微观非均质性。其中边长为160,300,300和1000μm的正方形视域面积可以分别作为上述4种岩性致密储层矿物微观非均质性代表视域面积;边长为200,300,300和800μm的正方形视域面积可以分别作为上述4种岩性的孔隙微观非均质性代表视域面积。由此可见,不同岩石类型的致密储层,其微观非均质性存在明显差异,其中砂岩微观非均质性>泥质粉砂岩、页岩微观非均质性>泥岩微观非均质性。综合矿物微观非均质性和孔隙微观非均质性,可将边长为200,300,300和1000μm的正方形视域面积分别作为研究区泥岩、页岩、泥质粉砂岩和砂岩致密储层微观非均质性的代表视域面积。

High-resolution scanning electron microscope(SEM)is the most intuitive method to study the heterogeneity of tight reservoirs,though the problem of representation of view area is yet to be solved.The tight reservoir of the third member of the Hetaoyuan Formation in the Biyang Sag is taken to quantitatively reveal the micro heterogeneity of tight reservoirs of diverse types with large-view splicing technology of field emission scanning electron microscope(FE-SEM).The results show that the main types of tight sandstone reservoir space in the study area include intergranular pores and intragranular pores,together with a few micro-fractures,and the shale reservoir space types are also dominated by intergranular and intragranular pores,with relatively few organic pores or micro-fractures.The micro heterogeneity of minerals and pores in tight reservoir rocks such as mudstone,shale,argillaceous siltstone and sandstone are discussed by combining FE-SEM technology with statistical method.The view area of a square with a side length of 160μm,300μm,300μm and 1000μm can be regarded as representative view area of mineral micro heterogeneity of the four lithological types of tight reservoirs mentioned above,and the view area of a square with a side length of 200μm,300μm,300μm and 800μm can be used as the representative view area of their pores’micro heterogeneity respectively.Thus it can be seen that there are marked differences in micro heterogeneity among different types of tight reservoirs,that is,the micro heterogeneity of sandstone,that of argillaceous siltstone and shale,and that of mudstone ever decreasing in order.Considering the micro heterogeneity of minerals and pores,the view area of a square with a side length of 200μm,300μm,300μm and 1000μm can be used,respectively,as the representative view area of micro heterogeneity of the mudstone,shale,argillaceous siltstone and sandstone reservoirs in the study area.