松辽盆地四方坨子地区上白垩统姚家组浅水三角洲实例分析

摘要

Sifangtuozi area is the key project for Jilin Oilfield to submit reserves and raise efficiency recently, but there is no breakthrough of Yaojia Formation due to the poor knowledge of scientific theories.Based on the data from 147 exploration wells and 300 development wells,focused on core observation from 25 coring wells,combined with petrological characteristics,sedimentary structures,seismic sections and modern sedimentary cases, the formations,sedimentary features and exploration prospects of the shallow water delta of Upper Cretaceous Yaojia Formation in Sifangtuozi area were analyzed.The result shows that Yaojia Formation can be divided into two third-order sequences(SQY1and SQY2+3)and six fourth-order sequences(RST).In the sedimentary period of Yaojia Formation,the paleo-topography grade is less than 3°,the paleo-depth is less than 20 m,and the dry and hot paleoclimate and opening of eastern Songliao Basin,jointly contributed to the development of shallow delta and shallow to semi-deep lacustrine sedimentary system.Specifically,the natural traits of the shallow water delta comprising features of traction current and short distanced depositional process with near-provenance, with the development of enforced hydrodynamics structures, are presenting as blanket shaped morphological characteristics and imbricated aggradations seismic facies.Integrated the delta of the Ganjiang River and the Mississippi River with the studied case,it is concluded that the large scaled bed-like sand bodies developed in depositional center, are with the characteristics of horizontal long distance propulsion and vertical extensive overlap in multistage. The above knowledge will be helpful to the exploration of subtle reservoirs in southern Songliao Basin scientifically.%松辽盆地四方坨子地区是吉林油田近年提储增效的主力区块,但上白垩统姚家组勘探长期未获得突破.基于147口探井和300口开发井资料,重点结合25口井岩心观察,以岩石学特征、沉积构造分析和地震切片为手段,结合现代沉积分析,探讨了该区上白垩统姚家组浅水三角洲的形成背景、沉积特征和勘探潜力.结果表明,姚家组可划分为2个三级层序(SQY1与SQY2+3)和6个四级层序(RST).姚家组沉积期,研究区古坡度小于3°、古水深小于20 m、干热的古气候与东部敞盆的古地理格局,促成发育浅水三角洲—滨浅湖—半深湖沉积体系.其浅水三角洲具备牵引流和"源近流短"的沉积特征,发育强水动力沉积构造,表现为毯式三角洲形态和叠瓦状加积地震反射.结合赣江和密西西比河三角洲实例认为,该区浅水三角洲发育的大规模湖盆中心薄层砂体,具有"平面长距离推进,垂向多期广覆式叠置"的特征,该认识对松辽盆地南部坳陷区隐蔽油气藏勘探具有参考价值.