Geological characteristics and controlling factors of the fourth member of Dengying Formation in Pengshen well 1-Dongba well 1

The Dengying Formation is an important oil and gas exploration layer in the central Sichuan Basin. In order to investigate the reservoir characteristics and genesis of the fourth member of the Dengying Formation in the Pengshen well 1-Dongba well 1 area, the rock type and reservoir space type of the fourth member of the Dengying Formation were analyzed through drilling core observation, rock thin section identification and permeability experiments. The results show that the reservoir rock types in the fourth member of the Dengying Formation of the study area include algal dolomite, mud powder crystal dolomite, breccia dolomite, and sandstone dolomite. The reservoir space is mainly composed of secondary dissolution pores, followed by residual primary pores and modified fractures. The development of dissolution pores has the characteristics of distribution along fractures and biological algae layers, and the development of dissolution pore pore fracture composite reservoirs has the characteristics of dissolution pore pore fracture type. According to the differences in genesis, the fourth member of Dengying Formation reservoir can be divided into three types: burial karstification type reservoirs, surface-buried superimposed modified reservoirs and structural hydrothermal modified reservoirs. Among them, the surface-buried superimposed modified reservoirs are concentrated at the top of the fourth member of the Dengying Formation. The sedimentation of the reef-beach body controls the composition of reservoir materials, develops early framework pores, controls the longitudinal distribution of the reservoir, controls the development and planar distribution of secondary dissolution pores through surface and buried karst processes, communicates with isolated pores through fracture development, promotes fluid dissolution, and increases reservoir permeability