摘要： 断陷湖盆作为全球最重要的含油气盆地类型之一,在盆地早期的充填演化过程中,其陡坡带往往能够形成厚达上千米的砂砾岩沉积建造,成为油气勘探的重要领域。目前对这些巨厚层砂砾岩的沉积成因认识仍存在较多的争议。本次研究以济阳坳陷典型的断陷湖盆——东营凹陷陡坡带盐家地区为例,基于高分辨率三维地震数据体、岩心、录井、测井等地质资料,综合运用地震地层学、构造地质学、沉积学和流变学分析方法,对前期在断陷湖盆陡坡带早期发现的斜向扇三角洲的发育特征及其形成演化机制进行了研究,取得了以下主要认识: (1)斜向扇三角洲沉积物中砾石含量相对较高,由牵引流和重力流共同形成,石英含量平均40%~55%,发育扇三角洲平原、扇三角洲前缘和前扇三角洲亚相,其地震响应特征在顺物源方向表现为(斜交、叠瓦和帚状)前积相,在垂直物源方向表现为充填相; (2)斜向扇三角洲主要发育于断陷早期,并于断陷中期大量消亡,扇体与边界断层以低角度斜交,角度通常不会超过45°,扇体的发育规模受到其根部所处位置的影响,扇体的消亡呈非等时性; (3)断陷湖盆陡坡带早期大型斜向扇三角洲的形成演化主要受控于4个因素: 边界断层分段特征形成的转换构造为斜向扇三角洲的发育提供输送通道,断陷早期边界断层控制下的古凹槽为斜向扇三角洲的发育提供可容纳空间,断块间相互作用形成的破碎带为斜向扇三角洲的发育提供物质来源以及边界断层的硬连接导致斜向扇三角洲的消亡并向近岸水下扇转换; (4)已发现断陷湖盆陡坡带深层砂砾岩油气藏多属于斜向扇三角洲。本次研究指出陡坡带各级别转换带可作为勘探的重点靶区,布井方向应沿斜交边界断层。本研究不仅丰富了断陷湖盆陡坡带沉积理论,同时能够为中国陆相断陷盆地深层勘探提供新的思路和理论依据。

关键词: 断陷湖盆陡坡带, 斜向扇三角洲, 演化, 展布特征, 深层油气, 东营凹陷

Abstract: As one of the most important types of oil and gas basins in the world,the rift lacustrine basin can often form glutenite sedimentary formations with a thickness of thousands of meters in the early stage of filling and evolution process,which has become an important field of oil and gas exploration. However,there are still many controversies regarding the sedimentary genesis of this extremely thick glutenite. In this study,Yanjia area in the steep slope zone of the Dongying sag,a typical rift lacustrine basin in Jiyang Depression,is selected as an example. Utilizing high-resolution 3D seismic data,core samples,logging,and well logging,we conduct a systematic analysis of the glutenite sedimentary formations in the steep slope zone during the early rifting stage. This study applies seismic stratigraphy,structural geology,sedimentology,and rheology analysis methods comprehensively. The following understandings have been obtained: (1)The gravel content in the sediments of oblique fan delta is relatively high,which is formed by traction flow and gravity flow. The average quartz content is about 40%-55%. Fan delta plain,fan delta front and pre-fan delta subfacies are developed. The seismic response characteristics include(oblique,imbricate and broom-shaped)progradation facies along the direction of sediment source,and filling facies perpendicular to the sediment source direction. (2)The oblique fan delta mainly developed in the early stage of rifting,and disappeared in the middle stage of rifting. The fan and the boundary fault are obliquely intersected at a low angle,typically not exceeding than 45°. The development scale of the fan is affected by the location of its root,and its disappearance is not isochronous. (3)A new mechanism for the formation of the large-scale oblique fan delta in the steep slope zone of the rift lacustrine basin during the early stage of rifting is proposed. Relay structures related to the segmentation characteristics of boundary faults provide transport conduits for the development of oblique fan deltas. The paleo-troughs controlled by the boundary fault activity provide new accommodation for the development of oblique fan deltas during the early stage of rifting. The fracture zone formed by the interaction between faulted blocks provide material basis for the development of oblique fan deltas,and the connection of the faulted block leads to the disappearance of the oblique fan delta and the transformation to the nearshore subaqueous fan. (4)It has been found that most of the deep glutenite reservoirs in the steep slope zone of the rift lacustrine basin belong to the oblique fan deltas. This study points out that the relay zones at all levels in the steep slope zone can be key target areas for exploration,and the well layout direction follow the oblique boundary fault. This study not only enriches the sedimentary theory of steep slope zone in rift lacustrine basin,but also provided a new idea and theoretical basis for deep petroleum exploration of the continental rift lacustrine basin in China.

Key words: steep slope zone of rift lacustrine basin, oblique fan delta, evolutionary, distribution feature, deep petroleum exploration, Dongying sag

中图分类号: 

• P512.2