渤海湾盆地沙南凹陷曹妃甸14-5区沙河街组砂体成因分析

西洼沙河街组沉积位于渤海湾盆地沙南凹陷,从Es3m到Es1,沙南凹陷经历四期裂陷幕,其间发育的不整合面T5使区域古地貌隆升,形成四期的三级层序变化旋回,并在西洼东—西向中央断裂带的控制下形成南、北物源和北部断裂坡折。双向物源和断裂坡折控制沙河街组沉积,形成多类型沉积,其中Es3m以半深湖—深湖、富泥质的湖底扇为特征,形成弱水动力沉积环境;Es3u以半深湖—深湖、富砂质的湖底扇和火山岩为特征,形成局部动荡的水动力沉积环境;Es12沉积较薄,形成独具特色的多样式、多类型沉积,包括半深湖—深湖、扇三角洲前缘、前缘斜坡扇、滑塌体、湖底扇及火山岩沉积,以及牵引流与重力流并存,以重力流为沉积主导。层段内的沉积序列及演化特征决定该区域形成南、北物源控制的4种成因砂体,南物源的晚期成砂机制,包括扇三角洲前缘砂、前缘斜坡扇砂,北物源的中晚期成砂机制,包括滑塌体砂和湖底扇砂。因此,西洼区域勘探以寻找岩性圈闭、构造—岩性圈闭为主,断裂与砂体的空间匹配关系决定了圈闭的有效性。

Origin analysis of Es sand body in Caofeidian 14-5 area of Shanan Depression in Bohai Bay Basin

Shahejie formation is thick layer in west sub-depression of Shanan depression in Bohai Bay Basin.From Es3m to Es1 the basin undergoes rifting III phase and rifting IV phase,between them there is T5 uncomformity.The regional formations first undertake subsidence and then uplift,and at last subsidence phase,so there are three three-order sequences.And every sequence developed with different sedimentary systems.So under control of central fault,north supply and south supply,and then break belt on the north area developed.In Es3m phase,semi-deep lacustrine,deep lacustrine,and mud-rich sublacustrine fan with weak hydrodynamic developed in Caofeidian 14-5 area.In Es3u phase,semi-deep lacustrine,deep lacustrine,and sand-rich sublacustrine fan and volcanic sediments developed in the north with partial strong hydrodynamic.In Es12 phase,kinds of sedimentary systems developed including semi-deep lacustrine and deep lacustrine,delta front,slope fan,slump,sublacustrine fan and volcanic.Traction current and gravity current sediments existed together in the study area,and gravity current sediments were the main body.Through above sedimentary evolution,exploration focuses on lithologic trap and construction-lothologic trap in the west sub-depression,especially good matching of faults and sand body in space leads to trap exploration success.Therefore,regional exploration should focus on finding different types of sand in thick mud.