黄河口凹陷西北部湖底扇的沉积演化及发育模式——以古近纪沙三下亚段为例

湖底扇是黄河口凹陷古近纪一种重要的沉积类型,扇体储集物性和含油性较好,具有勘探价值.研究黄河口凹陷沙河街组沙三下亚段岩心、测井、地震反射特征,认为A区含油砂岩体为在半深湖—深湖环境形成的2种类型湖底扇沉积.低位域时期发育远岸的深水浊积湖底扇;湖扩域和高位域时期发育由三角洲前缘砂体滑塌进入湖底堆积而成的滑塌浊积湖底扇.从空间分布看,深水浊积扇主要发育在低位域湖盆内二阶断裂的下降盘;滑塌浊积扇主要发育在研究区南部的断裂陡坡带,位于扇三角洲前方,且扇体规模较大,发育时间长.湖底扇的发育受沉积坡折和断裂坡折的控制.由于构造背景、湖平面变化及物源供应不同,湖底扇的位置、规模和形态也不尽相同.

Sedimentary evolution and depositional model of Paleogene sublacustrine fan in the northwest of Huanghekou Sag: Case study on the down Member 3 of Shahejie Formation

The sublacustrine fan,an important deposition of Paleogene in Huanghekou Sag,is characterized by both good physical character of reservoir and oil-bearing property,thus it of higher value for petroleum exploration.Through studying the formation mechanism,the main control factors,the lithology,logging curve features and seismic reflectance signature in the lower Member 3 of Shahejie Formation in Huanghekou Sag,it was found that the oil-bearing sand bodies in the Area A belonged to two kinds of sublacustrine fan deposition formed under semi-deep-lake to deep-lake environment.Deposition of the deep-water turbidite sublacustrine fan corresponded to low stand system tract;deposition of the slump turbidite sublacustrine fan corresponded to transgressive system tract and high stand system tract,which was formed by slumping delta front sand.Viewed from spatial distribution,the deep-water turbidite sublacustrine fan was mainly developed in the second-order fault downthrown of the basin,while the slump turbidite sublacustrine fan was distributed in the abrupt slope which located in the south of study area,and the extent of the fan in the front of fan delta was greater and longer than that in the north.The sublacustrine fan was controlled by faulted-topographic break and sedimentary-slope break.As a matter of fact,different tectonic background,lake level changes and provenance could result in different position,shape and size of sublacustrine fan.