THE INFLUENTIAL FACTORS AND CHARACTRISTICSOF TRIASSIC YANCHANG FORMATION RESERVIORIN LONGDONG AREA, ORDOS BASIN

Chang 3,Chang 6,Chang 7 and Chang 8 Triassic Yanchang formations are the main producing oil layers in Longdong area,Ordos basin.The reservoir-rock types in these formations are arkose,lithic arkose and litharenite with delta and lacustrine facies.Their compositional maturity is low and textural maturity is medium.The clastic rocks experienced compaction,cementation and dissolution,thus producing intergranular pores and secondary solution pores.In profile,the physical properties of Chang 3 reservoirs are the best and in plane,the physical properties of reservoirs in the northeast are obviously better than that in the southwest.Favorable reservoirs mostly occur in the sand bodies in delta-front underwater distributary river channel and river mouth bars.All the composition of clasts,grade scale,content of interstitial materials and diagensis have important effects on the reservoir properties.Six vertical distributional models of reservoir are identified in Yanchang formation in Longdong area.The ascend and descend of base-level cycle with high frequency are main factors which control the distribution of reservoir physical properties.