西湖凹陷砂岩自生高岭石发育特征及其对储层物性的影响

Characteristics of authigenic kaolinite in sandstones of Xihu Sag and it's impact on reservoir physical properties

从储层演化的角度来说,高岭石是砂岩储层中最常见的自生黏土矿物之一,通常出现在孔隙喉道中,是长石溶解和次生孔隙发育的指示矿物。以薄片鉴定、电镜扫描、X衍射分析等资料为基础,通过对西湖凹陷古近系、新近系影响储层质量的自生高岭石的分布特征及其形成机制的研究,认为西湖凹陷自生高岭石的含量和分布特点与成岩作用过程中有机酸和大气水对长石等铝硅酸盐的溶解作用有关;自生高岭石含量与储层物性之间具有较好的相关性;西斜坡平湖组具有比中央反转构造带平湖组明显高的自生高岭石含量,具有更好的成岩和次生孔隙形成条件;凹陷南部地区具有比北部地区相对较高的高岭石含量,有更好的次生孔隙形成条件与储层物性。

Kaolinite is one of the commonest authigenic clay minerals in sandstone reservoirs from the point of view of reservoir evolution. Kaolinite generally existed in pore-throat and is an indicator mineral of dissolution of feldspars and development of secondary pores. Based on thin-section identification, scanning electron microscope analysis, X-ray diffractometric measurement, and study of the distribution and forming mechanism of authigenic kaolinite which influenced quality of Paleogene and Neogene reservoirs in Xihu Sag, it was indicated that the content and distribution of authigenic kaolinite was related to the dissolution of aluminosilicate minerals like feldspars which dissolved by organic acid and meteoric water in the diagenesis process and the content of kaolinite was well correlated to reservoir physical properties. Content of kaolinite in Pinghu Formation of the west slope was obviously higher with better development conditions for diagenesis and secondary pores than that of center inversion structure belt. Content of kaolinite in the southern area of Xihu Sag was relatively higher with better development conditions for secondary pores and better reservoir quality than that of northern area.