Discovery of alkali diagenesis in overpressured compartment--By taking Che-66 fan body as an example

According to in-depth study of deep reservoir petrology of Che-66 wellblock in Chezhen sag,obvious quartz dissolution and the stable carbonate minerals occurrence have been found out,which reveals the overpressured compartment of the gravel rock is under the typical alkaline diagenetic environment.The pores of quartz dissolution type accounts for about 50% of the total reservoir porosity and its formation mechanism can be divided into three steps:theshaping of alkaline environment,the dissolution of quartz minerals,and the transformation of clay minerals.The influence of the alkaline diagenetic environment on reservoirs has two sides.One is the formation of quartz dissolution pores,and it plays a constructive role on reservoir quality.The other is that it is easy to precipitate massive calcite cement,filling parts of the micro fractures and secondary pores,and plays a destructive role.The fracture system composed by grain-edged joints and structural joints can be considered as a function of overpressure release and water-rock fluid channel,which can improve physical properties of deep reservoirs,favorable for hydrocarbon migration and accumulation,and good for high-quality glutenite reservoirs of 3rd member of Shahejie formation in Che-66 in overpressured compartment.