Reservoir Characteristics In The Second Section Of Bayingebi Of Wuliji Tectonic Zone,Chagan Depression

Chagan sag is one of sedimentary sags that are highly explored in the Yingen-Ejina Banner Basin.During the faulting period,the slope of the lacustrine margin is relatively steep.Under the control of near-shores,multi-sources,and small-sources,Fan belta and nearshore subaqueous have been developed in the second section of the Bayingebi of Wuliji tectonic zone.Based on the characteristics of coarse granularity,fast phase change and poor physical property,in order to find out the distribution of favorable reservoir,the studies of stratigraphic division and comparison,sedimentary facies and reservoir characteristics are carried out.Based on the theory of sequence stratigraphy and well logging geology,using the vertical cycle change of core observation and logging curve,the second section of Bayingebi Formation is divided into seven sand bed groups;.And on this basis,multiple stratigraphic frameworks are established,revealing the distribution of the stratigraphy in the horizontal direction.The study of sedimentary facies of K₁b₂ is carried out through core,logging,seismic data and the predecessors’research.And the study makes clear that they are most developed Nearshore Subaqueous Fans during the sedimentary period of K₁b₂^6K₁b₂⁷ section;they are mainly developed Fan belta during the sedimentary period of K₁b₂^1K₁b₂⁵ section.The sedimentary facies can be further divided into six subfacies which are composed of Nearshore Subaqueous Fans internal fans,intermediate fans and external fans,and fan delta front,fan delta plain.The reservoir rock of K₁b₂ is mainly composed of feldspar lithic sandstone.The reservoir properties are poor,with ultra-low porosity and ultra-low permeability.The porosity ranges from 1.2%to 15.32%with an average of 6.2%,and the permeability ranges from 0.003×10^-3μm² to158.6×10^-3μm²,with an average of 4.7×10^-3μm².The reservoir of K₁b₂ underwent mainly mechanical compaction,carbonate dissolution and late carbonate cementation,creating a secondary pore zone among 2300²900m.The K₁b₂ reservoir is mainly at the middle diagenetic A₂ stage.According to the characteristics of sedimentary facies,diagenesis,reservoir properties,and pore structure,the reservoir classification standard is established.And the reservoir type is mainly the classⅢandⅣ.Among them,the class III is the relatively better reservoir andⅣis poor reservoir.On the basis of the classification standard,the reservoir of K₁b₂ is evaluated.Taking K₁b₂⁶,K₁b₂² and K₁b₂¹ as an example,it is considered that the reservoir property of the K₁b₂² are the best in the longitudinal direction,and the reservoir in the south of Wuliji is better than other areas on the horizontal direction.