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.