RESERVOIR CHARACTERISTICS AND MAIN CONTROLLING FACTORS OF XISHANYAO FORMATION IN NIUJUANHUNAN-MAZHONG AREA,SAN-TANGHU BASIN
The Malang Sag in the Santanghu Basin of northeast Xinjiang is notable for the coexistence of multiple reservoir types,with the first member of the Middle Jurassic Xishanyao Formation(J2x1)in the Niuquanhunan-Mazhong area showing significant exploration potential.Despite this potential,there have been few studies on the characteristics and main controlling factors of the reservoir in this area.This paper investigates the reservoir characteristics and controlling factors of the first member of the Xishanyao For-mation in the Middle Jurassic through the analysis of extensive data from over 490 drilling wells,1,270 thin sections,1,197 cast thin sections,1,197 scanning electron microscopy samples,and 49 sets of mercu-ry compression data collected from the Niuquanhunan-Mazhong area.The results reveal that the reservoir sandstone of the first member of the Xishanyao Formation in the Niuquanhunan-Mazhong area is primarily feldspar lithic sandstone,with lithic sandstone being the secondary type.The average interstitial material content between the clasts is 4.78％,predominantly composed of cements.Diagenetic analysis indicates that the main pore types in the sandstone are residual primary intergranular pores,followed by intergranu-lar pores and intergranular dissolved pores.The average porosity of the sandstone reservoir is 12.23％,and the average permeability is 4.21×10-3 μm2.Furthermore,the sandstone reservoir exhibits poor sor-ting characteristics with small pore throats.The average separation coefficient of the mercury injection curve is 1.5,and the average maximum pore throat radius is 1.4 μm.The study of sedimentary facies in-dicates that both sedimentary microfacies and diagenesis significantly impact the physical properties of the sandstone reservoirs,with microfacies being the predominant factor.Among the various microfacies,the underwater distributary channel reservoirs exhibit the best physical properties,followed by the estuarine bar facies.Diagenesis has both positive and negative effects on reservoir physical properties.Compaction and cementation reduce the reservoir porosity by 19.03％and 4.78％,respectively,while dissolution in-creases porosity by 1.53％.Comprehensive diagenetic analysis shows that the diagenetic stage of the reser-voir rocks ranges from early diagenetic stage B to middle diagenetic stage A.The porosity of the rocks is reduced by compaction and cementation and increased by late-stage dissolution,which can create favorable reservoir spaces.The findings of this study provide an effective basis for selecting superior reservoirs in the Malang Sag,enhancing the understanding of reservoir characteristics and the main controlling factors,and guiding future exploration and development activities in the region.
sandstone reservoirreservoir qualitythe first member of Xishanyao FormationSangtang-hu Basin
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