Abstract: In order to solve the difficulty of entering the horizontal well of the Shan 2³ sand body of the Yulin Gas Field in the Ordos Basin and the problem of deviation of the wellbore from the gas layer after entering the window,the sedimentary sequence of more than 30 wells and the sedimentary rhythm of the Shan 2³ sand body in the Yulin Gas Field were studied.It is found that there are three sets of coal-bearing strata in the Shan 2 approximately the same distance to the Shan 2³ sand body,and the Shan 2³ sand body is superimposed by a plurality of positive cyclothemic vertical single sand bodies.Therefore,the coal-bearing strata were used as the marker to predict the top boundary of the Shan 2³ sand body,and the marker based window entering method for horizontal wells was developed.The sedimentary characteristics of the Shan 2³ sand body were combined with the variation characteristics of drilling time,cuttings,gas measurement and Gamma ray while drilling to establish the sedimentary cycle based horizontal section geo-steering technique.Through those techniques applied in the Well YuH1 and YuH2,sidetracking was eliminated,and the encountering rate of sandstone reached 98.2% and 95.6%,respectively.The marker layer method and the sedimentary cycle horizontal well guidance technology provide an efficient geosteering method for accurate horizontal window entry and improved sandstone drilling rate