Study on the sedimentary facies of Chang4+5 of Yanchang Formation in Triassic in Tiebiancheng area,Ordos Basin

Tiebiancheng area is located in nip depressed belt on south-north hunch belt between eastern steep slope and east-north slow slope in Etuokeqianqi-Yanchi-Huanxian-Qianyang area,the middle and western area of Ordos Basin.The main oil-bearing formation is Chang4+5 reservoir of Yanchang Formation,Triassic.The litho logical character,sedimentary structure and grain-size distribution of the reservoir are analyzed based on core data and logging data,and it is held that land facies river and lake dominated delta system develops in Chang4+5, and belong to bend flow river dominated delta system.The main microfacies include submerged distributaries channel,mouth bars,distal bar,distributaries separate bay,submerged bank and submerged burst fan.The relationship is studied between sedimentary facies and oil-bearing characteristics of the reservoir.The result of the study provides the support for prediction of favorable facies belts of the reservoir and next exploration.