鄂尔多斯盆地华庆地区长63重力流沉积特征

Characteristics of gravity flow sedimentation of Chang 63 in the Huaqing area,Ordos Basin

湖盆重力流沉积砂体是致密油勘探的有利目标区。综合利用岩心观察、分析化验及测录井资料,对鄂尔多斯盆地华庆地区长63砂层组重力流沉积类型、特征、主控因素及沉积模式展开了研究。研究表明:华庆地区长63砂层组沉积粒度细,粒度概率为上凸两段式,跳跃和悬浮总体发育,具有典型深水重力流沉积的层理构造;华庆地区重力流沉积划分为滑塌沉积、碎屑流沉积和浊流沉积3种类型,组成水道、朵叶及朵叶侧缘3种沉积微相。华庆地区长63深水重力流沉积发育主要受东北充足物源供给、足够湖盆水深、湖盆发育的深水坡折地形及延长期火山、地震等沉积事件影响,不同相带重力流沉积类型、砂体厚度与内部结构表现出明显差异性。在靠近三角洲源区以水道为主,由砂质碎屑流沉积和滑塌沉积组成,砂体薄而分布局限;中部沉积以朵叶为主,主要是砂质碎屑流沉积夹浊流沉积,沉积砂体垂向叠加,厚层展布;深湖区主要为朵叶侧缘,以浊流沉积为主,砂体呈薄互层分布。本研究不仅对湖盆重力流沉积认识有一定的补充作用,同时为后期重力流砂体中油气勘探与开发提供了重要地质依据。

The gravity flow sedimentary sand body found in a lake basin is considered a promising target area for tight oil exploration.In this study,we investigated the characteristics,main controlling factors,and sedimentary model of the Chang 63 sand group in the Huaqing area of the Ordos Basin,through core observation,analysis,and logging data.Our findings indicate that the sediments of the Chang 63 sand group in the Huaqing area have a fine grain size,with a probability of grain size distribution showing an upper convex two-stage type.The overall sedimentary structure is characterized by the development of jumping and suspension,typical of deep-water gravity flow deposits.We identified three types of gravity flow deposits in the Huaqing area:slump deposits,clastic flow deposits,and turbidity deposits.These deposits form three subfacies:channel,lobe,and lobe lateral.The development of deep-water gravity flow deposits in the Chang 63 area of the Huaqing area is primarily influenced by several factors.These include an abundant source supply in the Northeast,sufficient water depth in the lake basin,deep-water slope break topography in the lake basin,and volcanic and seismic sedimentary events of the Yanchang Formation.Notably,there are distinct differences in gravity flow deposition type,sand body thickness,and internal structure across different facies belts.In the vicinity of the delta source,the channel is mainly composed of slump deposits and some sandy debris flow deposits,with thin sand bodies and limited distribution.In the middle part of the sediment,the lobes consist mainly of sandy debris flow deposits,including some turbidity current deposits with vertically overlapping sedimentary sand bodies distributed as thick layers.In the deep lake area,the lateral margin of lobes is primarily composed of turbidity current deposits,with sand bodies distributed as thin interbeds.This study not only enhances our understanding of gravity flow sedimentation in lake basins but also provides a crucial geological foundation for future exploration and development of oil and gas resources in gravity flow sand bodies.