摘要：

浅水三角洲广泛发育于湖泊环境中，受到波浪的改造作用，可在其前端形成离岸滩坝沉积。湖盆浅水三角洲-离岸滩坝体系可作为重要的油气储层类型，其构型特征尚不清楚。本文综合利用岩心与密井网资料，对渤海湾盆地东营凹陷胜坨油田二区沙河街组二段2砂组砂体开展了精细构型解剖，结合基于Delft3D的沉积数值模拟结果，阐明了湖盆浅水三角洲-离岸滩坝体系构型特征与形成机理。研究认为，浅水三角洲-离岸滩坝体系在顺源方向上具有明显的相带分异特征，呈现浅水三角洲前缘-小规模滩砂-大规模坝砂-小规模滩坝砂的顺源演变规律。浅水三角洲前缘与大规模的离岸坝砂同时形成，两者之间发育后期形成小型滩砂。浅水三角洲前缘表现出波浪影响的特点，分流河道分支数量少、深切于河口坝中部，河口坝呈朵状，分流河道在前进到一定距离后决口在侧向形成新的河口坝。大规模透镜状的厚层坝砂形成于破浪带附近，最先发育于三角洲的侧前方滩砂两侧部位，由两个小型坝砂生长、拼接而成，具有平面双厚中心、剖面驼峰状的特点。河口坝与大规模坝砂的规模相对较大、宽厚比高，前者的长宽比较低，而后者的长宽比较大；近端与远端滩砂的规模较小，长宽比与宽厚比也较小。本文研究为东营凹陷胜坨油田剩余油的精细挖潜提供参考和借鉴。

关键词: 浅水三角洲, 离岸滩坝, 湖浪改造, 构型, 胜坨油田, 沉积数值模拟

Abstract:

Shallow water deltas are widely developed in lake environments. Under the modification of waves, offshore beach-bar deposits can be formed at the delta front. The shallow water delta-offshore beach-bar system in the lacustrine basin can be an important oil and gas reservoir type, and its architectural characteristics are still unclear. In this paper, the sand bodies of the 2nd submember of the 2nd member of the Eocene Shahejie Formation (Es₂) in the 2nd Block of Shengtuo Oilfield, Dongying Sag, Bohai Bay Basin were finely dissected by using core and abundant well data. Combined with the results of sedimentary numerical simulation based on Delft3D, the architectural characteristics and formative mechanism of the shallow water delta-offshore beach-bar system in the lacustrine basin were explained. The study believes that the shallow water delta-offshore beach-bar system has obvious facies differentiation characteristics along the provenance direction, showing the evolution law of shallow water delta front to small-scale beach sand to large-scale bar sand to small-scale beach-bar sand. The shallow water delta front and large-scale offshore bar sand were formed simultaneously, while the small-scale beach sands developed later in areas between them. The front of the shallow delta shows the characteristics of wave influence. The number of distributary channel branches is small and the distributary channel is deeply cut in the middle of the mouth bar. The mouth bar is in the shape of a fan. After the distributary channel has extended a certain distance, it avulses and forms a new mouth bar laterally. Large-scale lenticular thick bar sands are formed proximal to the surf zone, initially developing on both sides of delta-front shoreline sands through the growth and coalescence of two small bar units. These composite features display biconvex thickness maxima (dual-thick centers) with a characteristic humpbacked morphology. The scale of the mouth bar and the large-scale bar sand is relatively large and the aspect ratio is high. The length-to-width ratio of the former is low, while the length-to-width ratio of the latter is large; the scale of the proximal and distal beach sand is small, and the aspect ratio is also small. This study provides reference for the fine-scale potential tapping of remaining oil in the Shengtuo Oilfield of the Dongying Sag.

Key words: shallow water delta, offshore beach-bar, lake wave modification, architecture, Shengtuo Oilfield, sedimentary numerical simulation

中图分类号: 

• P618.13

• TE122