Diagenesis and Porosity Evolution in the Changxing Formation in Tongnanba Area,Northeast of Sichuan

The changing formation in tongnanba area,northeast of Sichuan basin has experienced 4 evolutionary stages,namely penecontemporaneous diagenatic stage,shallow burial early diagenetic stage,moderate burial anadiagenetic stage,deep burial late diagenatic stage.The major types of diagenesis include cementation,compaction,pressure solution,recrystallization,dolomitization,dissolution and tectonism,in which the dolomitization and dissolution are the major contributors to the improvement of poroperm characteristics of the reservoirs in deep burial diagenetic stage.In correspondence with the complicated diagenis,the porosity evolution also experienced 3 major evolutionary stages:the destroying of primary pores,formation of secondary pores and destruction of secondary pores.