Abstract: Since the initiation of oil and gas exploration and development in the Pearl River Mouth Basin,South China Sea,understanding of the Neogene marine reservoirs has been deepening.However,understanding of the deep reservoir quality is still weak due to the late initiation of deep exploration and development and the sparseness of offshore wells,thus is inefficient to guide exploration and development.By taking Oilfield A of Lufeng sag as an example,we compared the reservoir quality between the braided river delta facies in the Paleogene Wenchang Formation and the shorefacies in the Neogene Zhujiang Formation in respects of microscopic pore structure and macroscopic physical properties.In addition,we also analyzed the main controlling factors of the low porosity and permeability reservoirs in the Wenchang Formation,so as to guide development planning of this kind of oilfield.Results show that the reservoir quality of Oilfield A is generally controlled by the tectonic sedimentation,the sedimentation in turn controls the late diagenesis to some extent,resulting in the reservoir quality difference between the Zhujiang Formation and Wenchang Formation.Diagenesis is the major controlling factor of the low porosity and permeability reservoirs in the Wenchang Formation.Diagenesis weakens the control of original sedimentary fabric on reservoir quality.It lowers porosity and permeability of the reservoirs and influences the later development of the oilfield.

Key words: reservoir quality, diagenesis, low-permeability reservoir, Lufeng Sag, Pearl River Mouth Basin