Diagenesis of the Ordovician Carbonates in Bozhong Depression,Bohai Sea Area

There is long geological reconstruction of Ordovician carbonates in Bozhong Depression after its deposition.Different diagenetic transformation makes reservoir very complex,so identifying the different diagenetic environment has certain significance for the buried hill reservoir prediction.By using normal thin-sections,cast thin-sections,scanning electron microscope and cathodoluminescence,this paper analyses the main diagenetic environment in the research area through the normal seawater,atmospheric freshwater and burial diagenetic environment.The pore types are dominated by secondary pores caused by dissolution and fracture.The reservoir physical properties are characterized by medium reservoir with strongly heterogeneity.The carbon and oxygen isotopic analysis and inclusion analysis of carbonate reservoir,based on the regional tectonic evolution and microscopic characteristics,shows although dissolution may occur in atmospheric freshwater and burial diagenetic environment,the main influential factors were hypergene karstification during the Paleozoic to Mesozoic time.The long time leaching dissolution improves the reservoir physical properties,but the dissolution under burial diagenetic environment can be limited for shaping the reservoir physical properties.The primary factor for lowering the Ordovician reservoir physical properties should be the large scale cementation in deep burial environment during Neocene.