Diagenesis Evolution Of Carbonate Reservoirs In The Middle Permian Of Fenggang 2 Block,Guizhou Province

Qixia formation and Maokou formation of middle Permian are one of the most abundant Marine carbonate reservoirs in south China.Fenggang block 2 is an important area for shale gas exploration in northern guizhou province.Diagenesis study based on the compared 2 blocks is lack of the status quo,in the modern sedimentary geology and reservoir geology theory,under the guidance of Marine carbonate rocks in Permian as the research object,field outcrop section and drilling in the region has carried on the investigation and study,study mainly by means of mercury injection experiment research of reservoir physical characteristics,combined with the microscopic identification cathodoluminescence method was used to study the the middle Permian carbonate diagenesis,diagenesis evolution stages are analyzed in detail,discusses the diagenesis and porosity evolution of carbonate reservoir.The middle Permian qixia formation and maokou formation in fenggang block 2 are mainly Marine carbonate rocks.The main rock types include: bioclastic limestone,micritic limestone,dolomitic limestone and other Marine carbonate rocks.Qixia formation and maokou formation belong to open platform and restricted platform as a whole.The porosity of carbonate rocks in the study area ranges from 0.55% to 4.05% with an average value of 1.34%,while the permeability of rocks is distributed between 0.000000126-59.9md with an average value of 3.62 md,belonging to ultra-low porosity,ultra-low permeability reservoirs.The carbonate rocks of qixia formation and maokou formation in fenggang block 2 have undergone complex diagenetic evolution in the process of deposition,and the degree of participation of these diagenesis in reservoir construction in this area is not the same.Micritization,compaction,compaction and cementation play a destructive role in carbonate reservoirs.Dissolution,dolomization and fracture play a constructive role in the formation of large-scale carbonate reservoirs.Due to the low development of middle Permian dolomites in the study area,the constructive role can be ignored.The diagenesis of the middle Permian carbonate rocks in the study area can be divided into three stages: early diagenesis(quasi-syngenetic diagenesis),middle diagenesis,late diagenesis and epigenetic diagenesis.The corresponding relationship between diagenesis stage and diagenetic environment was established,the diagenetic sequence of carbonate rocks was established,and the pore evolution model of middle Permian carbonate reservoirs in fenggang block 2 was established.