Abstract: Multiple types of in-channel deposits with obvious characteristics are developed in the Lower Member of Minghuazhen Formation in Laibei low uplift, Bohai Bay Basin. Based on the comprehensive analysis of 3D seismic data, cores, logging, ancient organisms and clay minerals, this paper quantitatively studies the features of channels, and then discusses the evolution rule, controlling factors and their significance for oil and gas accumulation. Based on analyzing the plane shape, development scale, hydrodynamic conditions and sedimentary environment, the channels in the Lower Member of Minghuazhen Formation can be divided into five types:large high-curvature meandering channel, small low-curvature meandering channel, micro meandering channel, braided channel and underwater distributary channel. The evolution of channel patterns is mainly driven by tectonic subsidence rate and paleoclimate change. As the tectonic subsidence accelerated, the type of channel was transformed from large meandering river to small meandering river and braided river successively. The East Asian monsoon enhancement event occurred around 8.5 Ma ago resulted in increases in both rainfall and source supply. With the rapid lake transgression, the study area was transformed from the sedimentary environment of braided river to shallow water delta; taking underwater distributary channels as the skeleton and sheet sand body as the inter-channel sediments, the large continuous sandbody was developed in this area. Guided by this understanding, the Neogene lithologic traps of large continuous sandbody were discovered for the first time in Bohai oilfield, and KenLi6-1 oilfield with hundred million tons was successfully discovered, initiating a new model of "lithologic exploration for large continuous sand body".

Key words: KenLi6-1 oilfield, paleoclimate, channel evolution, large continuous sandbody, lithologic trap

摘要： 渤海湾盆地莱北低凸起明化镇组下段(明下段)下部发育特征明显、类型丰富的河道沉积,综合三维地震资料、岩心、测井、古生物、黏土矿物分析等地质资料,对河道特征进行定量研究,讨论了河道类型的演变规律、控制因素及其油气成藏意义。基于平面形态、发育规模、水动力条件、沉积环境分析,将明下段河道划分为5种类型:大型高弯度曲流河道、小型低弯度曲流河道、微型曲流河道、网状河道和水下分流河道。构造沉降速率和古气候变化是河道类型演化的主要驱动因素,随着构造沉降加速,河道由大型曲流河依次转化为小型曲流河、网状河。距今约8.5 Ma的东亚季风增强事件导致降雨量增加、物源供给增强,随着快速湖侵,研究区由网状河沉积环境转化为浅水三角洲,发育以水下分流河道为骨架、河道间席状砂为主体的大型连片砂体。在该认识指导下,渤海油田首次在新近系发现大型连片砂体岩性圈闭,并成功发现垦利6-1亿吨级油田,开创了"大砂体岩性勘探"新模式。

关键词: 垦利6-1油田, 古气候, 河道演化, 大型连片砂体, 岩性圈闭