涠西南凹陷南部斜坡带中段流一段湖底扇沉积特征研究及油气勘探

Sedimentary characteristics of sublacustrine fan in the first member of Liushagang Formation in middle section of southern slope in Weixinan Depression

涠西南凹陷为典型的箕状断陷盆地,广泛发育与湖底扇有关的岩性油气藏,本文以其中一个最为典型的湖底扇油气藏为例,从岩心、测井、地震多方面对湖底扇的岩石学特征、结构、构造特征进行了分析,认为流一段湖底扇比较发育,具有浊流沉积所形成的不同段数的鲍玛序列,在沉积结构上具有典型浊流沉积的粒度分布特征和沉积构造现象,另外在测井曲线和地震反射特征上也具有明显的浊流沉积响应。在此基础上分析了湖底扇的成因机制与分布规律,认为丰富的物源供给、一定的触发机制和较为发育的断裂坡折带的存在是该区湖底扇形成的重要条件。该区湖底扇沉积于中深湖环境中,封堵条件好,同时邻近生油洼陷,能够形成利于油气聚集的岩性圈闭,是勘探的有利目标。

Weixinan Depression is a typical halfgraben basin,which is widely developed lithologic reservoirs related to sublacustrine fan. Taking a typical sublacustrine fan reservoir as an example, the petrological characteristics and structural characteristics of the sublacustrine fan were analyzed from the aspects of core, logging, seism, etc. The results indicated that the sublacustrine fan of the first member of Liushagang Formation was relatively developed, having Bouma sequences of dif- ferent segment numbers formed from turbidity sediment and the granularity distribution characteristics and structure of typi- cal turbidity sediment. Besides, the logging curves and seismic reflection characteristics have obvious turbidity deposit re- sponse. On this basis, it was analyzed the formation mechanism and distribution law of the sublacustrine fan. The analysis results indicated that main conditions of the sublacustrine fan formation include rich source supply, some certain triggering mechanisms, and the existence of relative developed faulted slope - break zone. Meanwhile, the fan with good sealing condi- tion was deposited in mid - depth lake environment, and close to source sag. The fan is beneficial to forming the lithologic trap of hydrocarbon accumulation, which is a favorable exploration target.