Diagenesis of the Paleogene Clastic Reservoir and Their Relation with Reservoir Quality of Beidagang Oilfield in Huanghua Depression

This paper studies the diagenetic characteristics and the influencing factors related with the Paleogene clastic reservoir of Beidagang Oilfield in Huanghua Depression,based on a vast amount of data from rock thin section,scanning electron microscope,cathodoluminescence,X -ray diffraction and physical data,including the types and characteristics of diagenesis,diagenetic evolution stage,influencing factors of diagenesis,the classifications of diagenetic facies and the relation between diagenesis and reservoir quality.It is shown that the Dongying Formation reservoir is mainly in early diagenetic B stage with a partin middle diagenetic A1 stage;the Shahejie Formation reservoir is mainly in middle diagenetic A stage with a part in middle diagenetic B stage.The compaction and the cementation significantly reduce the primary pores and permeability,as the main causes of the poor physical properties,but the dissolution as the main factor helps the development of the secondary pores,which can improve the reservoir properties of the sandstones.The area of the sandstone reservoir can be divided into four diagenetic facies including compaction-consolidation facies,carbonate cementation facies,weak cementation facies and unstable clastic dissolution facies.The reservoir properties of sandstone controlled by unstable clastic dissolution facies are the best,those of the weak cementation facies are the second best,and those of the reservoir properties of sandstone controlled by carbonate cementation facies and compaction-consolidation facies are poor.The results of this study may provide guidance in finding favorable reservoirs in this region.