The diagenesis of carbonate rocks underwent through the entire period from the accumulation

burial to the uplifting of sediments.Because carbonate rocks were sensitive to the rock-forming environment

primary petrofabric and physical properties of rocks were constantly modified during the long time of diagenesis.Exam-ples are the complex diagenesis processes of the Changxing reef shoal dolomite and the Feixianguan oolitic beach dolomite in the Puguang gas field in northwest Sichuan.This paper focuses on the burial diagenesis through thin-sections of key wells in the Puguang gas field

and high precision 3D seism and cores data have been used to analyse the penecontemporaneous diagenesis environment.From the sedimentation of the Changxing Formation of the Upper Permian to the Feixianguan Formation of the Lower Triassic

most part of the Puguang gas field was lo-cated on the platform margin.Reef on the Changxing Formation platform margin

marginal beach and intraplat-form beach on the Feixianguan Formation platform composed the reservoir facies of the Puguang gas field.Limi-ted environment after and between reef beach has provided penetration-reflux conditions for penecontemporane-ous dolomitization.The study on thin-sections shows that the Permian Changxing Formation and the Triassic Feixianguan Formation underwent large-scale diagenesis processes like dolomitization

multistage cementation

compaction

multistage dissolution and fissure.The dolomitization generated intracrystalline pores and improved reservoir permeability.Early calcite cementing materials protected the original porosity from compaction.The se-lective dissolution of oolite formed moldic pores.The selective dissolution of non-fabric materials created en-larged pores or caverns.Tectonic fracture not only improved reservoir permeability but also served as the liquid migration channels to enlarge the dissolved fissure.Despite the heterogeneity of reef beach facies reservoirs

which was determined by various diagenesis processes and the complexity of depositional fabric

the original dep-ositional fabric of oolitic beach and reef beach facies controlled the distribution of potential reservoirs.