塔里木盆地寒武—奥陶系主要白云岩类型及孔隙发育特征

塔里木盆地寒武系和下奥陶统白云岩广泛发育,岩石类型复杂多样。按照结构和特殊构造两大分类依据,文中将研究区白云岩归为6大类,即泥-粉晶白云岩(又按含膏与否进一步分为含膏泥-粉晶白云岩和不含膏泥-粉晶白云岩)、粉-细晶白云岩、中-粗晶白云岩、斑状白云岩、藻纹层白云岩和膏溶角砾白云岩。每类白云岩都可以其独具特色的晶体结构和/或沉积构造与其他类型相区分。在这些白云岩中发育的孔隙类型主要有6种,即窗格孔、铸模孔、晶间孔、溶孔、角砾孔及砾间溶孔和缝合线孔,其中除窗格孔为原生孔隙外,其余均属次生孔隙。就其储集意义而言,以溶孔和晶间孔最为重要,次为角砾孔及砾间溶孔,而铸模孔和窗格孔的储集意义相对次要。缝合线孔的意义主要有二:一是可改善储集岩的渗透性,二是与斑状白云岩配合还可能构成有效储集岩。

Types and porosity characteristics of the Cambrian-Ordovician dolostones in Tarim basin

Cambrian-Ordovician dolostones in the Tarim basin are of various types and extensively distributed.Six dolostone types can be documented based on fabrics and special structures,which are mud-silt-sized dolostone,finely crystalline dolostone,coarse dolostone,patchy dolostone,algal laminated dolostone and gypsum-dissolved angular gravel dolostone.Furthermore,the mud-silt-sized dolostone can be divided into gypsiferous and non-gypsiferous.Every dolostone type can be differentiated from the others by its special crystal structure and/or sedimentary structures.Six main pore types were identified in the dolostones,which are fenestral,moldic,intercrystal,dissolved,breccia and dissolved breccia,and stylolite pores.Fenestral pores are primary and the others are secondary.The dissolved pore and intercrystal pore are the most important reservoir spaces,followed by breccias,and dissolved breccia pores,and the moldic and fenestral pores are less important.Stylolites can enhance the permeability of reservoir rocks;they can also enhance the capacity of reservoir and form better reservoir rocks when they are combined with patchy dolostone.