Based on the sedimentary and petroleum geology theory and through the observation of outcrops, cores, and slices and testing analysis, the authors study the Ordovician organic reefs on the west margin of Ordos Basin. The authors reach out a conclusion that the Ordovician organic reefs on the west margin of Ordos Basin are the coral reefs of the Lower Ordovician Zhuozishan Formation located in Wuhai Zhuozishan in the north, the stromatoporoids-sponge reefs of the Lower Ordovician Kelimoli Formation of Well Qitan 1 in the middle and the coral reefs of the Upper Ordovician Beiguoshan Formation in Shijiezigou in the south. The reefs in the north develop earlier than that in the south. The north reefs have grown 2 — 3 phases and that in the south 4 phases. The aquatic environment of the reefs in the north is relatively shallow and the reefs in the south has a deep aquatic environment. The coexistence of different shoals and the reefs develops the reef-bank reservoirs. The reservoir spaces are mainly the organic lattice poles and dissolved poles dissolved by fabrics selectively. The physical conditions show the reservoir property is poor. But, the reefs located on the platform margin are beneficial to developing the reef-bank reservoirs, so the platform margin can be the exploration target.%应用沉积学和石油地质学理论,通过野外剖面观测、岩心观察、室内薄片和测试分析,对鄂尔多斯盆地西缘奥陶纪生物礁进行了详细研究,认为有北部的乌海桌子山地区下奥陶统桌子山组珊瑚生物礁,中部的棋探1井下奥陶统克里摩里组层孔虫—海绵生物礁和南部的石节子沟上臭陶统背锅山组珊瑚生物礁.北部生物礁发育的时代早,南部晚；北段礁体生长发育2～3期,南段发育可达4期；北段及南段生物礁生长的水体环境相对较浅,中部相对较深.生物礁与各种滩共生,发育礁滩型储层,生物格架孔和组构选择性溶蚀的溶孔是其主要储集空间类型,物性条件显示其储集性能不佳；但是,生物礁处在有利于礁滩储层发育的台地边缘相带,可以作为油气勘探的重要目标.
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