Effect of coal-measure tight sandstone cementation on reservoir physical property in the south of Ordos Basin

The tight sandstone reservoir diagenesis of the Upper Paleozoic He-8 member in the south of Ordos basin is mainly based on compaction and cementation. Cementation is the most important diagenesis in the target member. Therefore,it is bound to have an effect on the porosity and permeability of reservoir. Based on cathode luminesce,SEM analyses and casting slice,the types and characteristics of cements are analyzed. As a result,the tight sandstone ce- mentation of He-8 member is divided into three main types including silicate cementation,carbonate cementation and mud cementation. Besides,according to the occurrence status of different cements,silicate cement is divided into Type I (contact cement),Type II (overgrowth-edge cement),and Type III (mosaic cement);carbonate cement is divided into Type I (porous cement),Type II ( particle replacement cement),Type III ( crystal stock cement) and Type IV ( base cement);and mud cement is divided into Type I (illite mud cement),Type II (clay matrix mud cement),Type III (chlorite grain-coating mud cement),and Type IV (kaolinite mud cement). Different cementing methods and the content of cement are not the same. By means of the quantitative analysis with Photoshop,the result shows that the par- ticle replacement cement has little effect on the reservoirs physical property. The overgrowth-edge cement is positive to the reservoir storage space when the cement content is less than 5% . The crystal stock cement is negative to the reser- voir storage space.