鄂尔多斯盆地镇北地区长8油层组自生绿泥石对储层物性的影响

自生绿泥石是砂岩储层中常见的成岩矿物,对储层物性具有重要影响。通过普通薄片、铸体薄片及扫描电镜观察,对鄂尔多斯盆地镇北地区长8油层组砂岩储层中自生绿泥石的形成机制及其对储层物性的影响进行了深入研究。研究表明:①该区自生绿泥石主要以黏土膜和玫瑰花状2种形式产出,黏土膜内层的颗粒黏土包膜自同沉积时期开始形成,转变为自生绿泥石后,黏土膜外层的孔隙衬里绿泥石于中成岩期呈叶状或针状垂直于内层包膜向孔隙方向生长;玫瑰花状绿泥石于晚成岩期在较大孔隙内形成。②自生绿泥石对储层物性的影响表现在2个方面:一方面自生绿泥石可通过改变孔隙微区环境及占据颗粒表面空间,阻止自生石英在碎屑石英表面成核来抑制石英次生加大,从而保存原生孔隙;另一方面自生绿泥石在保存原生孔隙的同时,占据了喉道空间,使砂岩储层的渗透性降低,其含量与渗透率呈负相关性。

Influence of authigenic chlorite on reservoir properties of Chang 8 oil reservoir set in Zhenbei area,Ordos Basin

The authigenic chlorite is frequently observed in sandstone and may heavily influence the reservoir properties.Based on observation of thin section,cast slices and scanning electronic microscope,we studied the mechanism of authigenic chlorite generation and its influences on sandstone reservoir properties of Chang 8 oil reservoir set in Zhenbei area of Ordos Basin.The results show that:①The authigenic chlorite is mainly presented in the form of chlorite coatings and chlorite rosettes,and the formation of internal layer of grain coatings began at the contemporaneous sedimentary stage.After the authigenic chlorite formed,pore-lining chlorite of outer layer grew towards the direction of the porosity perpendicular to the internal layer coatings by ctenoid at the mid-diagenetic stage.The formation of chlorite rosettes formed in the more capacious porosity at the late diagenetic stage.②The authigenic chlorite influenced the reservoir properties on two aspects:on the one hand,the authigenic chlorite is to the benefit of the preserve of primary porosity,it restrains the secondary enlargement of authigenic quartz by changing the porosity micro-environment and occupying the space on the detrital quartz surface;on the other hand,the permeability of the sandstone reservoir is reduced,although the authigenic chlorite has protected the primary porosity,it also occupies the space of throat,finally,it leads to the contents of authigenic chlorite is negative related to the permeability.