东营凹陷砂岩储层自生高岭石发育特征与成因机制

Development characteristics and genetic mechanism of authigenic kaolinite in sandstone reservoirs of the Dongying Sag,Bohai Bay Basin

通过大量薄片鉴定、岩心观察以及扫描电镜、粘土矿物粉晶衍射等分析测试手段,对东营凹陷砂岩储层中发育的高岭石的分布、产状以及镜下特征等进行了分析。结果表明,研究区砂岩储层中高岭石有自生和陆源两种成因。自生高岭石在储层中较为常见,其微观特征表现为结晶形态完整,呈典型的书页或蠕虫状充填于粒间孔和长石颗粒溶孔内,在铸体薄片中可见自生高岭石集合体呈"斑状"的聚集充填特征。陆源高岭石在研究区较为少见,一般在浅层出现,是在沉积过程中与碎屑颗粒等非粘土矿物同时形成。在上述研究的基础上,对自生高岭石成因机制进行了讨论,认为东营凹陷砂岩储层中长石类矿物的溶蚀作用是自生高岭石形成的主要物质来源。研究区粒度大、分选好的砂岩储层中高岭石含量较高,说明除酸性的流体环境和一定的物质供应外,流体动力条件也是自生高岭石形成的重要控制因素。

Arthroscopic characteristics,distribution and occurrence of kaolinite are analyzed through quantity thin section analysis,core observation,scanning electron microscope and X-ray powder diffraction. The results show that the kaolinite of sandstone reservoirs in Dongying Sag has two genetic types including authigenic kaolinite and terrigenous kaolinite. The authigenic kaolinites are common in the reservoirs. Microscopically,they show complete crystal form,and fill intergranular pores and dissolution pores of feldspar in typical sheet or vermicular shapes. The ＂spotted＂filling feature of the authitgenic kaolinite aggregates are clear on cast thin sections. The terrigenous kaolinites are rare and often occur in shallow layers. They are formed in association with the non-clay minerals like clastic particles in deposition process. Based on the study mentioned above,the genetic mechanism of authigenic kaolinite is discussed. It is supposed that feldspar dissolution is the main material source for the formation of authigenic kaolinite. Sandstones with large grain size and well sorting have high content of kaolinite,indicating that,in addition to acid fluid environment and sufficient material supply,strong fluid dynamic is also an important controlling factor of authigenic kaolinite formation.