Major Controlling Factors Of High Quality Reservoirs Of The Dongying Formation Of The CFD6-4 Oilfield In The Bozhong Sag

In this paper,the petrological characteristics,diagenesis characteristics,reservoir space and physical properties of the Dongying Formation reservoir in the CFD6-4 oilfield in the Bozhong sag are studied.The article is guided by sedimentary petrology,reservoir geology,petroleum geology and other theories,using basical geological data and regional geological data,combined with observation of rock slice,scanning electron microscopy,X-ray diffraction analysis,ion concentration test and other means.On this basis,this paper deeply studies the effects of sedimentary conditions and diagenesis on reservoir physical properties in the study area,and clarifies the main controlling factors of high-quality reservoir.The petrological characteristics show that the grain size of the Dongying Formation reservoir in the study area is mainly fine-medium sand,and the sandstone composition has low maturity.The sandstone type is dominated by lithic feldspar sandstone and feldspar lithic sandstone.The study of diagenesis shows that the compaction in the study area is mainly mechanical compaction;The cementation is mainly carbonate cementation,siliceous cementation,iron cementation and clay mineral cementation;the dissolution mainly includes feldspar,cuttings particles and cements;The diagenetic stage is the stage B of the early diagenetic stage to the stage A of the middle diagenetic stage.Reservoir storage space in the study area includes primary pores,dissolved intergranular pores,intragranular dissolved pores of feldspar and rock debris,intercrystalline pores,mold pores and a small amount of biological cavity pores.The research area is dominated by secondary pores,followed by primary pores,and a small number of micro-cracks formed by rigid grain under compression.By establishing the logging interpretation curve of porosity with depth in the study area,it can be found that there are obvious abnormal pore zones in the Dongying 2nd and Dongying 3rd formations of the study area.According to the physical property data classification,it can be seen that the reservoir types in the study area are mainly mesoporous infiltration,mesoporous hypotonic and mesoporous ultra-low permeability,low porosity and ultra-low permeability.The high-quality reservoirs in the study area are mainly controlled by factors such as sedimentary factors,diagenesis and tectonic movement.Sedimentary conditions are the pre-requisites for high-quality reservoirs in the study area.High-quality reservoirs are often located with dominant sedimentary microfacies.The parent rock types are rhyolite and andesite,which often become high-quality reservoirs.The areas with high content of cuttings of the two types of extruded rocks are easy to form secondary pores and improve the physical properties of the reservoirs.Larger size of grains also lays a good foundation for the formation of high quality reservoirs.Diagenesis is the main reason for the later changes of reservoir physical properties.The dissolution is the main reason for improving the physical properties of reservoirs.There are many abnormal pore development in the Dong 3 formation of the study area,which cannot be separated from the contribution of dissolution.The cementation is an important reason for the deterioration of physical properties in the study area.The Dong 1st formation has a poor cementation effect and lays a foundation for the formation of high-quality reservoirs.The influence of tectonic movement on reservoir physical properties is mainly reflected in the influence of tectonic compression movement and the uplift of the stratum near the boundary fault,which causes the reservoir to be subjected to atmospheric water leaching and improve the physical properties of the reservoir.In addition,the microscopic tectonic movement provides a good channel for fluid migration,increases the area of water-rock reaction,promotes the formation of secondary pores,and improves reservoir performance.