渤海湾盆地渤南洼陷古近系沙河街组二段沉积相特征及演化

Features and evolution of sedimentary facies in the second Member of Paleogene Shahejie Formation in Bonan Subsag,Bohai Bay Basin

为了查明渤海湾盆地渤南洼陷沙河街组二段沉积相分布与演化规律,为油气勘探寻找接替区,在岩心、测井、录井及地震综合研究的基础上,对沙河街组二段进行了砂层组划分与对比,进而圈定了各个时期沉积相的展布范围并总结了沉积演化规律。研究结果表明:渤南洼陷沙二段可划分为4个砂层组,各砂组依次向南逐层超覆,沉积范围不断扩大。洼陷周缘凸起带附近主要发育扇三角洲前缘沉积,以水下分流河道微相为主;其次为河口砂坝与水下分流间湾。洼陷内部以滨浅湖滩坝为主,按其成因可分为正常砂质滩坝、砂岩-碳酸盐岩混积型滩坝以及风暴成因滩坝三类,不同类型砂坝分布规律各不相同。沙二段整体呈湖盆不断扩张、沉积范围不断扩大、扇三角洲分布减少而滩坝沉积规模不断扩大的沉积演化特征。

In order to reveal the sedimentary facies distribution and evolution pattern of the 2nd Member of Shahejie For-mation in Bonan Subsag of Bohai Bay Basin and to find new target areas for future oil and gas exploration in Zhanhua de-pression,we classiffied and correlated the sand groups of the 2nd Member of Shahejie Formation,delineated the distribu-tion of sedimentary facies in different historical periods and summarized the sedimentary evolution pattern based on the comprehensive study of core,logging and seismic data.Four sand groups were identified in the 2 nd Member of the Shahejie Formation in Bonan Subsag.They overlap each other southwards and get larger progressively in distribution area.Near the uplift zone around the Bonan Subsag,fan delta front deposits are predominant and consist mainly of underwater distributa-ry channel microfacies, followed by channel mouth bar and subaquatic interdistributary embayments.Inside the Bonan Subsag,shore-shallow lacustrine beach bars are predominant and can be divided into three types with different distribu-tion patterns according to their origin,namely normal sandy beach bars,sandstone and carbonate mixed beach bars and storm beach bars.The sedimentary evolution of the 2nd Member of Shahejie Formation features in continuous enlarging of lake basin,progressive expanding of sedimentary range.decreasing of fan delta distribution area,and increasing of beach bar distribution area.