鄂南延长组长3段致密储层特征及相对优质储层形成机理

Characteristics of tight sandstones and forming mechanism of relative high-quality reservoir in Chang 3 member of Yanchang Formation in Xunyi area, Ordos Basin

通过岩石普通薄片、铸体薄片、扫描电镜、物性测试以及X线衍射等分析,研究鄂南旬邑地区延长组长3段对油气富集有利的相对高效储层的发育规律和主控因素。研究结果表明:研究区长3段经历了中等强度的压实作用,大量的云母和塑性岩屑的存在以及方解石连晶式胶结导致了储层的致密化;绿泥石薄膜的发育有效地阻止了石英等碎屑颗粒的次生加大,并增强了颗粒的抗压实能力,保护了原生孔隙和喉道,自生高岭石发育的晶间孔对储层物性具有一定的改善,自生伊利石的发育对储层发育没有影响;近地表暴露时期大气淡水的淋滤作用是长石被溶蚀产生大量次生孔隙的主要原因;三角洲前缘水下分流河道和河口坝微相,较少的云母、塑性岩屑(其质量分数小于25%)和方解石(其质量分数小于6%)和相对较多的自生绿泥石以及古地貌斜坡带大气淡水淋滤的叠合是相对优质储层形成的重要条件。

The development rules and main controlling factors of reservoir for oil and gas accumulation in the Chang 3 member of Yanchang Formation in Xunyi area, Ordos Basin were studied by analyzing the thin sections, scanning electron microscopy（SEM）, physical properties and X-ray diffraction. The results show that the medium intensitycompaction occurs in Chang 3 member, and reservoir densification is caused by the occurrence of a large number of mica and plastic clastic, and calcite-crystal stock cementation. The development of chlorite films has effectively prevented secondary quartz enlargement and retards the compaction, which favors the preservation of primary pores. The development of intercrystalline pores in authigenic kaolinite has certain improvement on reservoir physical property, while authigenic illite development has no effect on reservoir development. The subaerial exposure of the Yanchang Formation sandstone in Early Jurassic and consequent meteoric fresh-water leaching are the main reasons for a large number generated secondary porosity caused by feldspar corrosion. Underwater distributary channel of delta front, mouth bar, fewer mica, plastic clastic（mass fraction〈25%）, calcite（mass fraction〈6%）, relatively more chlorite, and meteoric fresh-water leaching are important conditions in the formation of relative high-quality reservoir.