Description Of Chang 4+5 Reservoir In Southeast Wangjiawan Area,Ordos Basin

The Chang 4+5 oil layer group of the Upper Triassic Yanchang Formation in the southeastern part of Wangjiawan is rich in oil and gas resources and has great development potential,and has now become the main oil-bearing interval in this area.Due to the relatively weak geological research of the oil reservoir in this area,the thickness of the oil layer and the oil-bearing grade are quite different,and the lateral changes are violent,resulting in a great change in production after the production is put into operation.Based on this,in order to further grasp the geological characteristics of the oil reservoirs in this area,the reservoir description research was carried out on the Chang 4+5 oil layer group in the study area,which provided a theoretical basis for the later numerical simulation and the rational development of the oilfield in the next step.Guided by the theory of sedimentology,oil and gas reservoir geology,petroleum geology,and fine reservoir description,this paper uses drilling,well logging,core data,casting thin sections,scanning electron microscopy,cathodoluminescence,and conventional mercury intrusion experiments to analyze the reservoir geology.Conduct systematic research,including stratigraphic division and comparison,sedimentary facies research,reservoir characteristics and classification evaluation,reservoir characteristics and main controlling factors of distribution,3D geological modeling.The research results show that:the Chang 4+5 oil layer group in the study area develops the delta plain subfacies,the sedimentary microfacies are distributary channels and inter-channels,and the distributary channels are distributed along the NS-EW direction.The rock type in the study area is feldspar sandstone,and the pore types are intergranular pores,feldspar dissolution pores,and intragranular dissolved pores.Pore throat types are small pores and micro throats,belonging to low porosity and ultra-low permeability sandstone reservoirs.Through the analysis of intralayer,interlayer and plane heterogeneity,it is believed that the reservoir heterogeneity of Chang 4+5₁ is stronger than that of Chang 4+5₂.According to the reservoir classification standard,the research area is divided into I,II and III reservoirs.The research area mainly develops two types of reservoirs,II and III,and locally develops small-scale type I reservoirs.The study area is dominated by lithologic reservoirs.The oil-bearing layers in the study area are mainly medium-fine sandstone with good physical properties.The water saturation of the oil layer is relatively high.Spots and oil traces,distributary channel sand bodies are the main enrichment areas of oil reservoirs,and the distribution of oil reservoirs is mainly affected by sedimentary facies,diagenesis and structure.The stochastic modeling method is used to establish the structural model,the sedimentary facies model and the attribute model（porosity,permeability,oil saturation model）.The comparison of the obtained geological knowledge and the analysis of the model data has a high degree of agreement,which has certain guiding significance for the later numerical simulation and the rational development of the oilfield in the next step.