东海盆地丽水凹陷仙桥低凸起构造特征及其控砂模式

The structural characteristics and sand controlling models of Xianqiao Low Uplift in Lishui Sag,East China Sea Shelf Basin

现有钻探成果表明,落实仙桥低凸起以东砂体发育范围是丽水凹陷北部下一步油气勘探部署的关键。以三维地震为基础,结合周边探井资料,开展构造演化、构造样式、断裂体系及断层活动性研究,分析仙桥低凸起构造特征,进而从构造角度总结低凸起对东部主洼的沉积控制作用。仙桥低凸起为丽水凹陷断陷期发育的坡垒构造,发育地垒和半地垒两种构造样式,西倾主控断层仙桥大断裂为初始裂陷期多条独立断层生长、连接发育而成的断裂带,断陷末期断层硬连接区逐渐演化为断裂转换带。强断陷期仙桥大断裂活动性强,低凸起沉积控制作用主要表现为断层控砂;断陷末期在断裂转换带疏导下水系越过低凸起输入东部主洼,形成转换带控砂。围绕断陷末期断裂转换带,在仙桥低凸起东部落实南、北两支大型三角洲沉积体,为该区的油气勘探明确了方向。

The present drilling results show that determining the distribution of sand bodies to the east of Xianqiao Low Uplift is the key to locating the next oil and gas exploration target in the northern Lishui Sag.Based on the 3D seismic data and the surrounding exploration wells,this paper studies the tectonic evolution,structural style,fault system,and fault activity,analyzes the structural characteristics of Xianqiao Low Uplift,then summarizes the sedimentary control of Xianqiao Low Uplift on the eastern sub-sag from the perspective of structure.Xianqiao Low Uplift in Lishui Sag is a slope-horst structure formed during rifting and develops two structural styles:horst and half-horst.The west-dipping Xianqiao Fault is the fault zone formed by the growth and linkage of a series of isolated faults during rift initiation stage.In the rift waning stage,the hard-connected fault zone gradually evolved into relay ramps.Due to the strong fault activity during the rift climax stage,the sedimentation to the east Xianqiao Low Uplift is mainly characterized by a fault-controlled depositional model.Then during the rift waning stage,the drainage system flowed across Xianqiao Low Uplift and entered the eastern sub-sag through relay ramps,forming a relay-ramp-controlled depositional model.In the eastern part of Xianqiao Low Uplift,two large deltas(at the north and the south) were identified around the relay ramp which formed in the rift waning stage,providing a clear direction for oil and gas exploration in this area.