Diagenesis Characteristics And Porosity Evolution Of Sandstone Reservoir Of Zhuhai Formation In Huizhou Sag

Based on the data of casting thin section,SEM,cathodoluminescence,X-ray diffraction,conventional mercury injection and grain size analysis,the petrological characteristics,diagenesis,physical properties,pore structure and pore evolution process of Zhuhai Formation reservoir in Huizhou Sag are studied comprehensively.By analyzing the main controlling factors of the reservoir,the classification and evaluation standard of the reservoir are established,and the favorable reservoir is predicted.The results show that Zhuhai Formation in Huizhou Sag is a sandstone reservoir with coarse sand as the main grain size.It mainly develops compaction,cementation and dissolution.The reservoir is a porous reservoir with average porosity of 18.7% and average permeability of 309.2m D.The physical properties are medium.There are obvious differences in the planes of Zhuhai Formation reservoir.According to its characteristics,the reservoir of Zhuhai formation in Huizhou Sag can be divided into four areas: western,eastern,northern and southern uplift area.The reservoirs in the western area are mainly lithic feldspar sandstone and feldspar quartz sandstone,which are in the stage A of middle diagenesis.They have strong cementation,moderate compaction and dissolution.There are many primary intergranular pores.The reservoirs are controlled by the sedimentary environment.The favorable reservoirs are in the beach bar sand body which is transformed by wave action at the underwater uplift.The eastern area reservoirs are mainly composed of lithic sandstone and feldspathic lithic sandstone,which are in the transitional stage of the middle diagenetic stage A and the middle diagenetic stage B.It has undergone strong compaction,moderate strength cementation,and strong dissolution.The pores are mainly intergranular dissolved pores.The reservoir is controlled by the diagenetic environment.Therefore,favorable reservoirs are in the main channel sand bodies and mouth dam sand bodies in the delta fronts that have shallow burial depth,low paleotemperature and strong hydrodynamic.The northern area reservoirs that are in the stage A of middle diagenesis are primarily feldspathic quartz sandstone and lithic quartz sandstone.The intensity of compaction is medium,and that of cementation and dissolution is not strong.Intragranular dissolved pores are the main type of pores.The reservoir is controlled by the original sedimentary conditions and diagenetic environment.Favorable reservoirs are the main channel sand bodies in the delta front,mouth dam sand bodies,and beach bar sand bodies on low uplifts.The southern uplift area reservoirs are mainly feldspathic lithic sandstone,which is in the transition stage of early diagenetic stage B and middle diagenetic stage A.The compaction in the southern area is the weakest;the cementation is strong;the dissolution is weak.The primary pores are the main type of pores.The reservoirs are controlled by the shallower burial depth,so the favorable reservoirs are widely distributed in the sand body of the uplift area.