Study On Sedimentary Microfacies And Single Sand Bodies Of Member K₂qn¹ In Hei 69 Block In Jilin Daqingzijing Oilfields

Block Hei-69 is a typical block of low-porosity and low-permeability fault-controlled lithologic oil reservoirs in the Daqingzijing oilfields in Jilin.Years of exploration and development practices have revealed geological problems in the K₂qn¹reservoir,such as unclear understanding of high-quality sedimentary microfacies types and insufficiently detailed subdivision of individual sand bodies,which require further in-depth study.The study area covers 115 km²with significant differences in well deployment density.The target layers of K₂qn¹sand bodies are mostly thin interbeds with complex vertical superposition relationships and rapid lateral facies changes.This paper carries out detailed work on layer subdivision and consistency comparison,identification of sedimentary microfacies on the layer plane,and fine characterization of individual sand bodies in the study area,aiming to improve geological understanding,determine favorable sedimentary facies zones distribution and individual sand body plane distribution,and provide support for well deployment and productivity enhancement.The research firstly carries out fine layer subdivision and establishes a chronostratigraphic framework;then,based on sedimentary facies markers,single well-interwell facies analysis is conducted,combined with geological statistical inversion of sand body prediction,revealing sedimentary microfacies information between wells and in sparse well networks,and completing sedimentary microfacies plane distribution characteristics at the layer level.On this basis,individual sand body characterization of each layer is carried out under the constraint of facies control,resolving composite channels into single-phase channel sand bodies and plotting individual layer plane distribution maps of the main layers.The study shows that the K₂qn¹ section in the study area is a long-term base-level cycle deposition,with four sand groups and 16 layers developed internally,among which layers 12 and 14 can be further divided into five individual layers.The main source of water system during the K₂qn¹period in the study area is the Baokang-Tongyu water system in the southwestern part of the basin,which develops shallow-water delta-front subfacies.Based on sedimentary facies markers,well-log facies patterns,and seismic facies,underwater distributary channel microfacies（subdivided into class I and II underwater distributary channel microfacies）,underwater distributary bay microfacies,sheet sand microfacies（subdivided into class I and II sheet sand microfacies）,and distal sand bar microfacies are identified.With the secondary rise and fall changes of the lake level during the K₂qn¹period in the study area,the shapes of the underwater distributary channels in each sand group change from sheet-like to reticulate,bifurcate,and meandering.The composite sand bodies in the K₂qn¹section of the study area are divided into four types,and seven spatial contact modes of individual sand bodies are summarized based on vertical and lateral division markers,namely,isolated,superposed,shear superposed,bay-separated,sheet sand-contacted,docking,and side-cutting.As the lake level gradually rises and the accommodation space increases,the superposition style evolves from shear superposed to isolated and side-cutting to bay-separated.Based on the quantitative parameter characterization of individual sand bodies in the dense well network area,the average width of single-phase underwater distributary channels in the study area is 274.02m-383.33m,and the average thickness is 3.51m-4.31m,which guides the prediction of individual sand bodies in the sparse well network area.The basic characteristics of the remaining oil distribution are pointed out according to the influence of the development pattern of individual sand bodies on the effect of remaining crude oil injection and recovery in the study area.