Bongor盆地N油田下白垩统PⅠ油组扇三角洲前缘沉积模式及构型演化

Sedimentary model and architecture evolution of fan delta front in Lower Cretaceous PⅠOil Formation of N Oilfield in Bongor Basin

扇三角洲沉积体是陆相湖盆重要的油气储集体,确定储层内部砂体叠置关系是油田后期增储上产的关键。以Bongor盆地N油田下白垩统PⅠ油组为例,基于岩心、测井和地震资料,识别井下单砂体,分析扇三角洲前缘内部构型单元,建立由低位域期、湖侵域期到高位域期的扇三角洲前缘内部构型,研究砂体叠置样式的演化规律。结果表明:扇三角洲前缘发育水下分流河道、河口坝、席状砂及水下分流间湾4类微相,其中水下分流河道和河口坝为主要的单砂体类型,与四级构型单元相对应,存在切叠型、接触型和孤立型3类叠置样式。由低位域期、湖侵域期到高位域期演化过程中,扇三角洲前缘的砂体由高角度前积式、退积式到加积式、低角度前积式变化;平面上,表现为由长帚状、小朵状到大朵状演化。低位域期,具有水下分流河道构型优势,砂体以切叠型为主;湖侵域期,砂体发育有限,以孤立型为主;高位域期,河口坝和水下分流河道构型同时发育,演化为接触型。层序演化控制扇三角洲前缘内部砂体叠置样式与构型展布规律。该结果对扇三角洲前缘储层构型演化及油田后期开发和剩余油挖潜具有指导意义。

The fan delta body is an important oil and gas reservoir in the margin of continental lake basin.It is the key to increase storage and production of the oilfield to clarify the superimposition relationship of its internal sand bodies.Taking the Lower Cretaceous PⅠOil Formation of N Oilfield in Bongor Basin as an example,by integrating core,logging and seismic data,authors identified single sand bodies in the dense well network,analyzed the internal configuration unit of fan delta front,and established the evolution law of the internal architecture and sand body superposition style of fan delta front in the process of complete sequence from lowstand domain,lake transgression domain to highstand domain.The results show that four types of microfacies can be identified in the front of the fan delta,including underwater distributary channel,estuarine bar,sheet sand and underwater interdistributary bay.Among them,underwater distributary channel and estuarine bar are the main single sand body types and correspond to the fourth order architecture unit.There are three types of overlapping styles:tangent type,contact type and isolated type.In the process of evolution from lowstand and lake transgression to highstand domain,the sand body of fan delta front changes from high angle progradation and retrogradation to low angle progradation and aggradation,and changes from long broom,small flower to large flower on the plane.The lowstand stage has the advantage of underwater distributary channel architecture.The sand body is mainly cut and stacked.The development of the sand body in the lake transgression stage is limited.The sand body is mainly isolated.In the highstand stage,the mouth bar and underwater distributary channel architecture are developed at the same time.The sand body evolution is mainly contact type.Sequence evolution controls the superimposition style and architecture distribution of sand bodies in the fan delta front.The results show that the evolution of the fan delta front reservoir architecture,the later development of the oilfield and the tapping of the remaining oil are of great significance.