断陷湖盆陡坡带砂砾岩扇体成藏动力学特征——以东营凹陷为例

东营凹陷北部陡坡带主要发育了冲积扇、扇三角洲、近岸水下扇、陡坡深水浊积扇和滑塌浊积扇5种类型的砂砾岩扇体。以这些砂砾岩扇体为储层的油藏呈群带状沿陡坡带有规律展布,由边缘凸起向生烃洼陷中心依次形成了地层-岩性油气藏、构造-岩性油气藏和岩性油气藏。陡坡带内发育沙河街组四段和三段两套优质烃源岩,最大厚度大于4000m,有机质类型为Ⅰ、Ⅱ型,有机碳为0.5%～3.5%;陡坡带中、上部发育的扇体以断裂、砂层和层序界面组成的复合油气输导体系为通道,油气运移以纵、横向转换传递的阶梯状输导为主,为间接充注成藏。由于断阶发育,砂体岩性较粗、储集物性较好等因素在时空上的有机配置,致使扇体油气藏的油气生成、运移和聚集成藏具有多期性,即经历了东营组、馆陶组和明化镇组沉积期的三期油气充注过程,但以馆陶组和明化镇组沉积期的成藏为主,其成藏动力学过程概括为陡坡带断阶型砂砾岩扇体成藏模式。

CHARACTERISTICS OF RESERVOIRING DYNAMIC ON THE SAND-CONGLOMERATE FANBODIES IN THE STEEP-SLOPE BELT OF CONTINENTAL FAULT BASIN:A CASE STUDY ON DONGYING DEPRESSION

Five types of sand-conglomerate fanbodies,including alluvial fan, fandelta, coastal submerged fan, steep-slope deep water turbidite fan and slump turbidite fan,are developed on the northern steep-slope belt of Dongying depression. From the marginal salient to the basin's hydrocarbon-generating center, the oil reservoirs in these sand-conglomerate fanbodies are successively the stratigraphic-lithologic reservoirs,structural-lithologic reservoirs and lithologic reservoirs.In the steep-slope belt,the 4th member and 3rd member of Shahejie Formation are excellent source rocks,with a maximum thickness of 4000m, where the type I-II kerogen are present.The organic-carbon content for both source rocks ranges from 0.5 to 3.5 percent.Oil and gas were moved into the fanbodies,developed on the middle-upper parts of steep-slope belt,through the composite conduit system consisting of faults,sand layers and sequence boundaries,which is characterized by stepped migration in vertical and lateral transformation.The oil reservoirs in the fanbodies experienced the hydrocarbon-charging stages corresponding to the deposition periods of Dongying,Guantao and Minghuazhen Formations.The reservoiring process,however,occurred mainly during the deposition of Guantao and Minghuazhen Formations.The dynamic process of oil and gas accumulation can be summarized as the reservoiring model of the fault terrace type of the sand-conglomerate fanbodies in steep-slope belt.