Diagenesis of the Upper Permian Panlongdong organic reefs in northeastern Sichuan

The diagenetic types of the Upper Permian Panlongdong organic reefs in northeastern Sichuan consist mainly of cementation, neomorphism, dolomitization, dedolomitization, pressolution and dissolution. The study of cementation textures and mineralogy of the cements shows that the diagenetic environments of organic reefs in the study area evolved from the submarine environment to the meteoric vadose and underflow environments to the mixed sea water-fresh water environment and finally to the burial diagenetic environment. The dolostones in the study area are originated from mixed dolomitization. The regional dolomitization and dissolution are demonstrated to make greater contributions to the increase in porosity and potential reservoir space for oil and gas accumulation, and thus have important significance for the oil and gas exploration and assessment.