Reservoir Diagenesis of the Intermediate Section in Member 3 of Shahejie Formation(Paleogene) in Niuzhuang Subsag, Shandong Province

Key words: 
• reservoir /
• diagenesis /
• reservoir quality /
• intermediate section of Member 3 of Shahejie Formation /
• Paleogene /
• Niuzhuang Subsag /
• Shandong Province

Abstract: Reservoir rocks of the intermediate section of Member 3 of Shahejie Formation of Paleogene in Niuzhuang Subsag, Shandong Province, mainly consists of feldspathic litharenite and litharenite arkose with low compositional maturity and textural maturity. Diagenesis of the sandstones includes compaction, cementation, replacement and dissolution. Compaction includes five occurehces, they are brittle cracking of rigid grains, lined and concavoconvex intergranular contacts, apparently directional arrangement of framework grains, compressional deformation of plastic grains or intercalation of rigid grains in deformational grains, pseudomatrixization of compressional deformed ductile detrital grains. Cements are argilla, carbonates, authigenic clay minerals, quartz and feldspars. Replacement includes quartz replaced feldspars, carbonate cements replaced quartz, feldspars and lithic fragments, and carbonates cements replaced each other. Dissolution of grains mainly are quartz, feldspars and lithic fragments, and of cements of carbonate minerals. The research result shows that the diagenesis of reservoir rock is in Asubstage of telodiagenesis. The main factors which affect the diagenesis of the reservoir include rock composition, sedimentary environment and property of pore fluid. The influences of diagenesis on the reservoir physical properties are mainly the change of porosity and permeability. Compaction and cementation of the reservoir rocks makes the primary pores and permeability decreased quickly, which is the main causes of the poor physical properties; but dissolution of the reservoir rocks is the main factor of the development of the secondary pores, which can improve the physical properties of the reservoir sandstones.