Genesis and exploration significance of calcareous intercalation of Jurassic Xishanyao Formation in Luliang area,Junggar Basin
Based on core description,cast thin slice,scanning electron microscopy,conventional logging,CT,XRD,production dynamics and other data,the development characteristics,genesis,distribution pattern and 3D model of calcareous intercalation of Jurassic Xishanyao Formation in well 9 area of Luliang Oilfield are studied by means of hierarchical structure analysis,multi-dimensional interactive reservoir configuration characterization,3D embedded intercalation modeling and reservoir numerical simulation.The results showed that:(1)The cal-careous intercalations are mainly distributed in the densified medium and fine sandstone,and are typical physical intercalations.Its physical properties are characterized by extremely low porosity and low permeability,and it is a typical physical intercalation with"three low and two high"logging response characteristics.(2)The abundant sediment supply from underwater distributary channels and the mineralization process of bioclastic debris at the delta front,where dissolved Ca2+and CO32-are converted into solid calcium carbonate,provide the sedimentary material basis for the formation of calcareous layers.Calcareous layers primarily form during the diagenetic stage.Based on their genesis,they can be divided into two main types:one type is the cementation of thin sand layers within the proximity of mudstone formations,and those are calcareous cementation of diagenetic evolu-tion;the other type develops in river channel sand bodies with good physical properties and connectivity,specifi-cally at the base and overlapping areas of the channels,where secondary porosity is filled and cemented in pores.(3)It is mainly distributed of calcareous intercalation,with a thickness of about 0.25-2.00 m,a length of about 200-1 300 m and a width of about 100-900 m.The planar distribution is relatively continuous,and the direction of vertical material source varies greatly,and it is thin layer lenticular.(4)The calcareous interlayer has obvious control over the distribution of residual oil,forming residual oil-rich zones in the form of lenses and strips,etc.The residual oil in the study area is mainly distributed in J2x41-3 and J2x42-1 layers.
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