渤海沙垒田地区新近系明下段多河型地震地貌学特征

渤海沙垒田地区新近系明化镇组下段主要发育河流相沉积,是渤海地区浅层油气勘探的重点。利用地震地貌学方法结合现代河流体系卫星照片,在重点区的若干典型地层切片中识别出顺直河、中—低弯度曲流河(弯曲度1.2~1.8)及辫状河等多种河流地貌类型,并在明下上亚段沉积阶段发现了辫状河、曲流河共存现象。古沉积坡降分析表明,在整体宽缓的沉积背景下,顺直河、曲流河坡降整体偏小,辫状河坡降相对较大。利用地貌—水动力关系进行古流量估算,认为辫状河满岸流量最大可达3 942 m ^3 /s,曲流河满岸流量最小为145 m^ 3 /s,顺直河满岸流量一般小于300 m^ 3 /s。基于坡降—流量进行河流类型的判别,可增进对研究区不同河型发育特征、多河型地貌、辫曲共存现象及复杂河道砂体空间展布的认识。

Seismic geomorphological characteristics of multiple fluvial patterns in the Neogene Lower Minghuazhen Member in the Shaleitian area,Bohai Sea

Fluvial deposits are well developed in the lower member of Neogene Minghuazhen Formation in the Shaleitian area, Bohai Sea, which are perceived as the main targets of hydrocarbon exploration for shallow-buried reservoirs in the offshore Bohai Bay Basin. Combined with seismic geomorphological approach and satellites photographs of modern fluvial systems, straight river, low-to medium-sinuosity meandering river (sinuosity 1.2-1.8) and braided river can be well recognized from several typical slices in the study area. And the coexistence of braided and meandering rivers can be well interpreted during the deposition of the upper submember of the Lower Minghuazhen Member. According to the reconstruction of paleoslope gradient, the slope gradients of straight and meandering rivers are relatively lower, while they are particularly larger in braided rivers on a gentle-dipping slope. Within the paleodischarge estimation from the geomorphology-hydraulics relation, the bankfull discharge of braided rivers can reach 3 942 m3/s, while meandering rivers can be as low as 145 m3/s. The bankfull discharges of straight rivers are usually less than 300 m3/s. The discrimination of fluvial patterns based on slope gradient and discharge will enhance the understanding of different fluvial patterns, and will provide an important guidance of the geomorphological characteristics of multiple fluvial patterns, the coexistence of braided and meandering rivers and spatial distribution of composite fluvial sandbodies.