白云岩物质组分与结构对微孔储集体系形成的制约--以塔里木盆地下古生界白云岩为例

Dolomite Composition and Texture Constrain the Formation of Micropore Reservoir:An Example from Low Paleozoic Dolomite,Tarim Basin

塔里木盆地下古生界白云岩是重要的油气储层,由于经历了长期而复杂的成岩演化过程,其储集空间以次生孔隙为主,其中微孔储集体系分布广泛,很不均匀,并且规律性不强。通过对大量白云岩岩心薄片与显微照片的观察,结合电子探针分析,认为埋藏过程中白云石与方解石的差异溶蚀是微孔储集体系形成的主要方式,白云岩的物质组分与微观结构对白云岩微孔的形成具有重要的制约作用;从白云岩成分上来讲,含灰云岩与灰质云岩是白云岩储层的主要岩性;白云岩中方解石的溶解与否,受方解石赋存状态的制约。根据白云岩显微结构中方解石和白云石两者之间的关系,将储集物性较好的粒状白云岩大致分为3个亚类,即粒间填隙型、粒内包含型、包含—填隙混合型,其中以第1种形式即"粒间填隙型"分布的方解石最容易被溶蚀并形成次生孔隙,包含—填隙混合型次之,粒内包含型最差。

The lower Paleozoic dolomite sequences are important petroleum reservoirs in the Tarim basin. After a long and complex diagenetic process, the secondary dissolution pores are the main reservoir spaces. The distribution of the micro-porosities is wide and not uniform. The diverse-dissolution between calcite and dolomite during the burial is considered as an important mechanism for the micro-porosities reservoir system＇s formation based on the observation of plenty of well thin sections and micro-photos, as well as the EPMA data, and this process is constrained by the components and textures of dolomite despite the influence of fluids. Limestone bearing dolomite and calcitic dolomite are the main reservoir rocks with reference to the component of dolomite. However, not all the calcite can be dissolved during the burial process. The distribution type of the calcite in the dolomite has been used to subdivide the sucrosic dolomite into three types, including intercrystalline filling type, innercrystalline filling type and inter-innercrystalline filling mixed type, and the intercrystalline filling sucrosic dolomite can form fine micro-porosities during burial dissolution.