摘要： 中非裂谷系Doseo盆地Kedeni组油气勘探获重大突破,但对该主力层系层序地层和沉积充填方面的认识仍不明确,成为制约下一步油气勘探的关键。以Doseo盆地东部坳陷Kedeni组为研究对象,运用层序地层学及沉积学理论,结合岩心、测录井和地震资料,明确了Kedeni组层序地层格架及沉积体系展布。研究表明: Kedeni组可识别出3个层序界面,划分为2个三级层序(SQⅠ、SQⅡ),对应于2个“湖进—湖退”旋回。Kedeni组沉积物主要来自4个方向,并发育6种沉积相类型,沉积相展布具有东西分异、垂向继承发育的特征。正常三角洲分布于东南部缓坡带及中央低凸带,辫状河三角洲主要分布于东北部长轴方向和南部陡坡带,扇三角洲和近岸水下扇发育于北部陡坡带边界断层下降盘,湖底扇主要分布于西部凹陷深湖区。纵向上,SQⅠ层序的骨架砂体规模整体大于SQⅡ层序,且在每个三级层序内部,低位域和湖侵域组成的下部单元中三角洲—水下扇砂体更为发育。Kedeni组层序与沉积演化主要受到主干断层的构造活动、“南多北少”的物源供给、“半干旱—湿润”气候的转变等因素控制。在层序—沉积模式指导下,认为北部陡坡带小规模扇三角洲前缘—近岸水下扇砂体、南部及东北部大范围正常三角洲前缘、辫状河三角洲前缘砂体及西部凹陷深湖区湖底扇砂体可作为区内有利储集层的勘探目标。

关键词: 乍得Doseo盆地, Kedeni组, 层序地层, 沉积特征, 沉积模式

Abstract: A significant breakthrough has been made in hydrocarbon exploration in the Kedeni Formation of the Doseo Basin in the Central African Rift System. However,the stratigraphy and sedimentary infill of this dominant formation are still unclear,which has become a key constraint for the next step of hydrocarbon exploration. In this study,the Kedeni Formation in the Eastern Depression of Doseo Basin is taken as the research object. Based on the theory of seismic stratigraphy and sedimentology,combined with the core,logging and seismic data,the sequence stratigraphic framework and sedimentary system distribution of Kedeni Formation are clarified. The research results demonstrate that the Kedeni Formation exhibits three identifiable sequence interfaces,dividing into two third-order sequences(SQⅠ and SQⅡ),in response to two ‘transgressive-regressive’ cycles. The sediments of Kedeni Formation mainly came from four directions,and six types of sedimentary facies were developed. Distribution of sedimentary facies was characterized by east-west differentiation and features of vertical inheritance. Normal delta were distributed in the southeastern gentle slope zone and the central low uplift zone,whereas the braided river delta were primarily distributed in the long axis direction of the northeast and the southern steep slope zone. The fan delta and the nearshore subaqueous fan developed in the downthrown side of the boundary fault in the northern steep slope zone. The sublacustrine fan were mainly distributed in the deep lake area of the western sag. Vertically,the framework sandstone scale of the SQⅠ was larger than that of the SQⅡ,and in each third-order sequence,the delta-subaqueous fan was more developed in the lower unit composed of a lowstand system tract and a transgressive system tract. The sequence and sedimentary evolution of the Kedeni Formation were primarily controlled by factors such as the structural activity of major faults,differential sediment supply from the south to the north,and shifts in climate from semi-arid to humid conditions. Under the guidance of sequence-sedimentary model,it is considered that the small-scale fan delta front-nearshore subaqueous fan sandstone in the northern steep-slope zone,the large-scale normal delta front and braided river delta front sandstone in the south and northeast,and the sublacustrine fan sandstone in the deep lake area of the western sag can be regarded as favorable exploration targets within the region.

Key words: Chad Doseo Basin, Kedeni Formation, sequence stratigraphy, sedimentary characteristics, sedimentary model

中图分类号: 

• P531