基于可容纳空间变化的河流相演化新模式及其控藏作用——以莱州湾凹陷垦利A构造为例

为了厘清莱州湾凹陷馆陶组油气差异成藏机理，应用层序地层学原理，结合岩心、钻井、测井、地震等资料，对莱州湾凹陷垦利A构造馆陶组沉积期的沉积基准面及可容纳空间变化规律进行研究，建立了层序地层格架与河流相沉积演化模式，分析了河流相储层的控藏作用。结果表明：①馆陶组作为三级层序，内部可划分为3个体系域，由早期高可容纳空间体系域、低可容纳空间体系域和晚期高可容纳空间体系域构成。②馆陶组发育网状河、辫状河和曲流河3种河流相类型，受不同体系域的影响，三者在纵向上不断演化，导致储层垂向相变以及平面差异分布较为明显。③不同河流相的差异性决定了不同的油藏特征，早期发育的网状河储层侧向上相互切割拼接，垂向上存在稳定的泥岩夹层，导致横向连通性较好、垂向连通性较差，形成岩性-构造油藏；中期发育的辫状河储层在侧向和垂向上往复切割、相互叠置，侧向与垂向连通性均较好，形成构造-层状油藏；晚期发育的曲流河储层受大套泥岩隔层阻隔，侧向及垂向连通性均较差，形成孤立的岩性油藏。以上认识可为研究区的下一步勘探评价提供新的依据。

A new model for sedimentary evolution of fluvial faices based on accommodation space change and its impact on hydrocarbon accumulation: a case study of Kenli-A structure in Laizhouwan Depression

In order to clarify the differential accumulation mechanism of Guantao Formation in Laizhouwan Depression,the sequence stratigraphic framework and the sedimentary evolution pattern were established by using sequence stratigraphic theories,core and well-logging analysis and seismic data,and a new model for fluvial facies reservoir characterization was proposed which emphasized the fluctuation of sedimentary base level and the change of accommodation space. The results show that:(1)The Guantao Formation was a third-order sequence,and it was divided into three system tracts including early-stage high accommodation system tract,low accommodation system tract and late-stage high accommodation system tract.(2)Three fluvial facies were recognized in the study area including anastomosing river,braided river and meandering river. Each fluvial facie indicated a distinctive system tract,and the evolutionary process of fluvial facies was affected by the change of system tracts,which resulted in the vertical and lateral distribution differences of reservoir sand bodies.(3)The sand body distribution features of different fluvial facies controlled the hydrocarbon migration and accumulation:the anastomosing river sand bodies which had well lateral connectivity and poor vertical connectivity formed structurallithologic oil reservoir;the braided river sand bodies indicated predominant superimposition with well lateral and vertical connectivity,which became effective pathway for hydrocarbon migration and accumulation in structural high position and formed structural-formation oil reservoir;the meandering river sand bodies which were surrounded by thick mudstone had poor lateral and vertical connectivity,and formed isolated lithologic oil reservoir,thus the coupling relationship of oil-migrating faults and reservoir sand bodies was crucial to hydrocarbon accumulation.