On the basis of the sequence stratigraphic classification for Liushagang Formation of Weixinan Sag, the fine sedimentary facies studies are conducted: analyze the forming conditions and trap types of the subtle traps so as to guide the exploration of the subtle oil reservoirs. The studies show that Liushagang Formation is mainly characterized by the following four favorable conditions: multiple-period tectonic movements, multiple-time lake surface changes, various sedimentary facies types, favorable sand percentage and so forth. Two principal Lypes of subtle trap are developed; the lithologlcal trap including the fault-lithologic trap and updip pinch out trap etc. in the background of the structures; pure lithological trap maintaining nearshore subaqueous fan, slump turbidite, mouth bar and distal bar of the delta front without structural background. In the drilling practice of Weixinan Sag, the oil and gas are all discovered in different degrees in the following traps.%在涠西南凹陷流沙港组层序地层划分基础上开展精细沉积相研究,分析隐蔽圈闭的形成条件和圈闭类型,指导隐蔽油藏勘探.研究认为流沙港组具有多期构造运动、多次湖平面变化、多方向物源、多沉积相类型、砂岩体积分数适合等形成隐蔽圈闭的有利条件,主要发育2种隐蔽圈闭类型,即构造背景下的断层-岩性、砂岩上倾尖灭等岩性圈闭类型和无构造背景的近岸水下扇、滑塌浊积体、湖底扇、三角洲前缘河口坝及远砂坝等纯岩性圈闭类型.在涠西南凹陷的钻探实践中,以上类型圈闭均获得不同程度的油气发现.
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