Diagenesis of Paleogene Glutenite Reservoir and Its Control on Physical Property in the North Zone of Chezhen Sag

Key words: 
• the north zone of Chezhen sag /
• glutenite /
• diagenesis /
• physical property

Abstract: Based on a combination of core information, thin-section identification, an analysis of core properties and related analysis-testing data, the diagenesis of Palaeogene glutenite reservoir and its control on physical property in the north zone of Chezhen sag have been studied. Studies have shown that diagenesis is characterized by compaction, cementation, dissolution, lime-mud matrix recrystallization and metasomatism, the diagenetic environment underwent an evolution of alkalescence→acid→alkalescence→acid→alkalescence, and the corresponding diagenetic evolution sequence is compaction→feldspar dissolution/early quartz overgrowth→carbonate cementation/quartz dissolution→feldspar dissolution/carbonate dissolution/late quartz overgrowth→pyrite cementation. The glutenite reservoirs in research area have low porosity and permeability, and the reservoir space is mainly composed of secondary pores and cracks. The difference in lithofacies and diagenesis of different subfacies results in the difference in physical property. The inner fan is mainly composed of matrix-supported or grain-supported conglomerate,whose diagenesis is characterized by compaction or lime-mud matrix recrystallization, so dry layers develop widely in this kind of subfacies. Dissolution is intense in the middle fan, which effectively improves the reservoirs' property, so the rate of effective reservoir is high in this part. As for the fan marginal subfacies, intense cementation makes the property worse, regional dissolution makes the reservoir effective.