东海西湖凹陷平湖斜坡带平湖组沉积体系平面分区特征及差异性展布

Distributional signatures of depositional system of Pinghu Formation,Pinghu slope,Xihu Sag,East China Sea Shelf Basin

东海陆架盆地西湖凹陷平湖斜坡带始新统平湖组是目前已证实的主力油气富集层系,对其沉积体系已开展过多轮研究,但是仍然存在很大争议。在前人研究的基础上,基于新处理的三维地震、岩心和多种地球化学测试等资料,对平湖斜坡带平湖组沉积环境和沉积体系重新展开了系统分析。平湖斜坡带主要发育三种沉积体系类型:河控三角洲、潮汐改造为主的三角洲和潮坪沉积体系。这三种沉积类型在平面上具有明显的分区性,平北地区以河控三角洲沉积为主,平中地区发育受潮汐改造的三角洲沉积,平南地区处于半封闭海湾湾口,以潮坪体系为主,洋流控制着砂体的空间展布形态和规模。整体而言,平湖斜坡带平湖组沉积格局从北向南表现出受海水影响逐渐加强的变化规律。

The Eocene Pinghu Formation on the Pinghu slope of Xihu Sag of East China Sea Shelf Basin is a main confirmed strata for hydrocarbon enrichment.At present,many studies have been carried out on its sedi⁃mentary system,but certain controversies are still existed.On the basis of previous studies and newly processed 3D seismic,core and geochemical data,it was re⁃analyzed in this paper for the sedimentary system of Pinghu Formation.Results show that there are three types of sedimentary system on the slope belt:river⁃controlled delta,tidal⁃transformed delta and tidal flat depositional system.These three types of sedimentary modes have obvious zoning characteristics in plane.The northern area is dominated by river⁃controlled delta deposits.The middle area is dominated by tidal⁃transformed delta deposits.The southern area is in the mouth of a semi⁃closed bay,dominated by tidal flat system,and ocean currents control the spatial distribution shape and scale of sand bodies.It is concluded that the influence of seawater on the sedimentary pattern of the Pinghu Formation in the slope belt is strengthening from north to south.