Abstract: To analyze diagenesis of clastic rock in upper part of the 4^th member of Shahejie Formation (Es₄ ^s) in Bonan sag of Jiyang depression and its quantified influence on porous development and find favorable reservoirs, casting slices, scan electronic microscope and X-ray diffraction are used to study the relevant data. The results indicate that compactness, cementation, dissolution and metasomatism occurred in the clastic rock reservoir of Es₄ ^s in Bonan sag. Influenced by alkali fluid from early–stage gypsum and organic acid from latestage hydrocarbon source rock, the gypsum reservoir experienced the alkali and acid diagenetic environment. Controlled by the diagenetic environment, there were mainly cementing pores in the clastic rock reservoir in the early diagenesis and dissolving pores occurred in the middle diagenesis. Based on a large amount of analytic and testing data about different depths and horizons, the quantitative characterization method of pore development is established for the time being. The clastic rock reservoir in the low-level system domain, with development of secondary pores, is distributed in the southern and northern delta frontal area and eastern fan delta plain of Bonan sag, while the clasitc rock reservoir with development of primary pores is distributed on sandstone beach bar. The clastic rock reservoir in the high-level system domain, with development of secondary pores, is distributed in the end of the northern near-bank underwater fan and southern fan delta plain of Bonan sag, while the clastic rock reservoir with development of primary pores is distributed in the frontal area of fan delta.

Key words: porous development, diagenetic environment, favorable reservoir, Bonan sag, Es₄ ^s