Diagenesis and reservoir porosity evolution of Western Slope Zone of Xihu Sag

The main types of reservoir rocks in the Western Slope Zone are feldspathic lithic sandstone and lithic arkose sandstone, and reservoir space is dominated by the intergranular and intragranular dissolution pores. Bases on core observation, combining with scan-ning transmission electron microscope and physical property analysis, it is realized that diagenesis and pore evolution have exerted great effects on the properties of reservoir. Study results showed that the reservoir has experienced complex diagenetic events, including com-paction, cementation, dissolution and replacement. The diagenetis stage can be divided into early diagenetic A and B stage and lately diagenetic A1, A2 and B, and now reservoir has entered into A2 stage. Most primary pores were destroyed after diagenetic evolution, and it is mainly secondary pores now. The two secondary dissolved porous belts have formed, one between 2 900 and 3 200 meters deep, and the other between 3 600 and 4 000 meters deep.