Reservoir Characteristics And Influencing Factors Of The Mid-oligocene In The Deep Water Area Of The Qiongdongnan Basin

The deep-water area of the Qiongdongnan Basin is rich in oil and gas resources.In recent years,major discoveries have been made and it is gradually becoming an important area for the growth of my country’s oil and gas resources.However,due to the low degree of exploration,and limited by the lack of exploration drilling and laboratory analysis data,previous studies mainly focused on structural evolution characteristics,source rock geochemical characteristics,analysis of accumulation conditions,sediment filling evolution,etc.,but the research on the formation and evolution mechanisms of deep-water reservoirs is relatively weak.This paper takes the Miocene-Oligocene Lingshui Formation,Sanya Formation,and Meishan Formation reservoirs in the deep water area of the Qiongdongnan Basin as the research object,based on previous studies.Using casting thin section,scanning electron microscope,clay mineral XRD test,fluid inclusion uniform temperature test,laser Raman analysis,electronic probe and other experimental methods,combined with the drilling data of6 wells in the study area,from the petrological characteristics and storage space Comprehensive analysis of reservoir characteristics in deep water areas from three aspects:physical characteristics and diagenetic characteristics.The influencing factors of reservoir development are studied from theer aspects:sedimentation,diagenesis and fluid charging.Finally,classify and evaluate the reservoirs in the study area to provide a geological basis for exploration and development.The results of the study show that the Miocene-Oligocene reservoir sandstone in the Qiongdongnan Basin is dominated by feldspar quartz sandstone and lithic quartz sandstone,and iron calcite and iron dolomite cements are developed,and are dominated by pore cementation,showing secondary quartz Increase and uneven distribution of clay minerals.The overall physical properties of the reservoirs are poor,mainly with medium porosity and low permeability.The eastern zone is mainly low-medium porosity,and the western zone mainly develops medium-low porosity and medium-low permeability reservoirs.The overall physical properties of the upper eastern zone are better than those in the west zone.Sandstone pores are dominated by residual intergranular pores,but also developed intergranular dissolved pores,intragranular dissolved pores,and a small amount of intercrystalline pores and micro-cracks.Reservoir pores often appear in a combined form,with residual intergranular pores+intergranular dissolved pores and intergranular+intragranular dissolved pores dominated.Compaction,cementation,dissolution and fracture are the main diagenesis experienced by the reservoirs in the study area.The diagenetic evolution of the reservoir sandstone in the Sanya-Lingshui Formation in the study area is generally in the middle diagenesis phase A₁-A₂period,and a small amount reaches the middle diagenesis phase B period.The diagenetic evolution of the Meishan Formation sandstone is relatively slow,and is generally in the middle diagenesis phase A₁-A₂period.The diagenetic evolution sequence is:compaction→calcite and dolomite cementation metastitution→organic acid dissolution→quartz secondary growth and strong dissolution of feldspar→iron calcite and iron dolomite cementation metastitution→quartz and enlarged edge dissolution→a small amount of iron calcite Dissolution.There are 2-4 carbonate cementation and 2-3 siliceous cementation in the reservoir.The reservoirs in the study area are mainly affected by three factors:sedimentation,diagenesis and fluid charging.The shallow marine facies and submarine fans are the sedimentary facies with good physical properties in the east and west regions,respectively.Compaction and cementation affect the storage The pores of the stratum are seriously damaged,and the amount of pores increased by dissolution is small.Fluid filling has an important influence on the formation of abnormal pore development belts.The higher geothermal gradient in the east region accelerates the diagenetic evolution.Reservoirs in the study area can be divided into types I-IV,where type I is high-quality reservoirs,type II and III are medium reservoirs,and type IV is poor reservoirs.