Comparative study of the eastern and western Chang 81 submember in Huanjiang area,Ordos Basin
There are obvious differences in reservoir properties between the eastern and western parts of Chang 81 submember of the Triassic Yanchang Formation in Huanjiang area,Ordos Basin,which results in different oil reservoir enrichment regularity between the eastern and western parts of Huanjiang area.By means of core observation,logging curve comparison,rock thin section identification and mercury injection curve analysis,this paper has clarified the basic reservior characteristics of the eastern and western Chang 81 submember of the Triassic Yanchang Formation in Huanjiang area,and then analyzed the tight genesis of the reservoirs in the studied area and the main controlling factors of the different properties between the eastern and western reservoirs.The research results showed that:① The eastern and western rocks of Chang 8i submember in Huanjiang area are mainly composed of lithic arkose and feldspathic lithic sandstones.The grain size in the west is coarser than that in the east.The pores are dominated by the remaining primary intergranular pores,followed by secondary feldspar dissolved pores,with high content of matrix.②Reservoir properties between the eastern and western parts are huge.The porosity and permeability in western Shancheng and Luoshanchuan area are 10.71％and 6.44 mD,developeing the low porosity and ultra-low permeability reservoirs,in which a considerable part can reach medium porosity and low permeability.In the estern studied area,the porosity and permeability of Dabazui-Laochikou to Hongde area are 5.63％and 0.13 mD,which are basically ultra-low porosity and ultra-low permeability tight reservoirs.③Sediment source supply,sedimentation and paleotopography are the inborn factors that the reservoir physical properties in the western part of the studied area are better than those in the eastern part.Among them,sedimentation and paleotopography control the macroscopic characteristics of reservoir sand body thickness and spatialdistribution,andsedimentsourcesupplyaffectsthemicroscopiccharacteristics of reservoir sedimentary rock particle size distribution and interstitial material distribution.And diagenesis is a key factor to reduce the eastern and western areas overall reservoir physical properties.
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