Chagan Sag is a Mesozoic sedimentary sag,the second section of Bayingebi is the main hydrocarbon generation interval. Fan delta surrounds the sag,and the fan delta sedimentary is of coarse granularity,fast phase change and poor physical property. The main controlling factors of hydrocarbon accumulation are effective reservoir. Based on the studies of precipitation facies,diagenesis,reservoir prediction about the mechanism of effective reservoir generation and distribution,we understand that physical properties of different facies of fan delta are largely different,and plain subfacies is of high content of glutenin of matrix,poor sorting and reservoir density;outside frontal subfacies is of thin rock granularity,weak hydrodynamic,high shale content and poor reservoir physical property;in front distributary channel microfacies is fine microconglomerate and gritstone of fine sorting and low shale content. Calcium cementation compaction plays an inhibitory effect in the early diagenesis,which creates the conditions for later dissolution,and Alkaline sedimentary environment and diagenetic evolution of sedimentary are helpful to form dissolution pores. In Chagan Sag,hydrocarbon accumulation has the characteristics of oil and gas storing in frontal fan delta-plain block-close range migration in the store-the tectonic setting control. Based on the above understanding, we focus on the anatomy of the Wuliji structure zone,and make a breakthrough of the thin oil exploration in the fan delta front.%查干凹陷是中生代的沉积凹陷，巴音戈壁组二段是主力生烃层段，扇三角洲环凹分布，但扇三角洲沉积粒度粗、相变快、物性差，储层有效性是油气成藏的主控因素。针对有效储层的形成机制和分布，开展了沉积相、成岩作用、储层预测等方面的研究。认为，扇三角洲不同相带储集物性差别较大，平原相砂砾岩杂基含量高、分选差，储层致密；外前缘相岩石粒度偏细，水动力弱，泥质含量高，储层物性较差；扇三角洲内前缘分流河道微相岩石多为细砾岩、粗砂岩，分选较好，泥质含量较低，成岩早期的钙质胶结作用对压实起到抑制作用，为后期溶蚀作用创造了条件，碱性沉积环境及其储层的成岩演化史有利于形成溶蚀孔隙。油气成藏具有扇三角洲前缘储-平原封堵-源内近距离运移-构造背景控藏的特点。在上述认识基础上，优选乌力吉构造带重点解剖，在扇三角洲前缘钻探获得突破。
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