Abstract: This study investigated the lithology and reservoir characteristics of the glutenite reservoir in the Niubao Formation of the Lunpola Basin using core, thin section and physical property analysis, and SEM data. In particular, several factors of rock compaction were analyzed from the viewpoint of diagenesis, and the relationship and sequential order between diagenesis and oil emplacement was investigated with reference to favorable conditions for pore formation. This study investigates for the first time the developmental process of reservoir pores. The results show that the reservoir space mainly comprises residual pores. A mixed sedimentation environment, relatively weak resistance to mechanical compaction, and intense carbonate cementation in the mid-late diagenetic phase are the three leading causes of reservoir compaction. Dissolution of soluble parties by acidic fluids is the main factor controlling the formation of secondary pores, whereas oil emplacement favors porosity preservation in that it causes dissolution and enlargement in some pores and forms oil films in the periphery to prevent carbonate cementation. Compaction causes significant damage to the reservoir during the shallow burial stage. As burial depth increases, acid dissolution and quartz overgrowth are enhanced and oil emplacement takes place. These lead to the formation of early carbonate cements. In the mid-late diagenesis, iron-containing carbonate cements replace early carbonate minerals and block most of the pores. The late-stage tectonic compression that follows leads to cracking in the reservoir. Based on the above, it can be concluded that pores are first formed among the primary grains, and then eliminated by compaction. Acid dissolution enlarges the pores, while oil emplacement preserves porosity and carbonate cementation destroys pores. The overlap between regions with sufficient oil emplacement and those with weak carbonate cementation is favorable for porosity preservation.

Key words: porosity preservation region, pore formation, compaction, glutenite, Niubao Formation, Lunpola Basin