CHARACTERISTICS OF TRANSFORM FAULTS IN THE XIHU SAG AND THEIR SIGNIFICANCE TO HYDROCARBON ACCUMULATION
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摘要:
西湖凹陷油气资源丰富,凹陷中部存在大量的挤压反转和转换断裂痕迹,转换断裂对油气的聚集与分布有着密切的关系。基于三维地震资料、重磁场特征及地层厚度,对凹陷内断裂类型和平面剖面特征进行了系统分析,在此基础上识别出3组大型转换断裂带。西湖凹陷平面上主要发育NE-NNE向断裂,主发育期主要位于古新世早期至始新世平湖组沉积期,可分为上、中、下3期断裂体系,转换断裂主要发育在上部断裂体系内。在“南北分区”大背景下,凹陷存在3组主要的大型转换断裂带:舟山-国头转换断裂带、海礁湾南缘转换断裂带和海礁湾北缘转换断裂带。大型转换断裂带对西湖凹陷具有重要的控圈和控藏作用,在其背景下发育多种构造样式和圈闭类型,包括扭动分叉“Y”型圈闭、扭动转换“H”型圈闭和扭动改造“Y”型圈闭等。同时,结合海礁湾南缘转换断裂带上已成藏油气田解剖,分析了转换断裂作为运移通道对油气的二次运移的重要意义。
Abstract:There are many reversed compressional and transform faults in the middle of the Xihu Sag. The transform faults are the ones controlling the accumulation and distribution of oil and gas. Based on 3D seismic data, gravity data, and stratigraphic thickness changes, the types and distribution patterns of faults in planes and vertical sections are studied in this paper. The sag is dominated by NE-NNE faults formed in the Pinghu stage of early Paleocene to Eocene. The faults may be roughly grouped into three fault systems: upper, middle, and lower, and the transform fault is mainly developed in the upper system. Three groups of transform faults, i.e. the Zhoushan-Guotou fault zone, the Southern Haijiao Bay fault zone, and the Northern Haijiao Bay fault zone are identified. Large transform fault zones play significant roles in trap formation and hydrocarbon accumulation. Many types of structures and trap types, such as the twisted and bifurcated “Y” shaped traps, the twisted and transformed “H” shaped traps and the twisted and reformed “Y” shaped traps are mainly developed on the background of the transform fault zone. In combination with the case analysis of oil and gas fields in the transform fault zones of Southern Haijiao Bay, it is concluded that the transform faults, as a migration channel, is of critical significance to the secondary migration of oil and gas.
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Key words:
- Xihu Sag /
- fault distribution /
- transform fault /
- trap-controlling processt /
- secondary migration
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图 2 西湖凹陷构造剖面图及断层断距(剖面位置见图1)
Figure 2.
图 5 西湖凹陷孔雀亭构造平湖组底断裂分布及西斜坡转换断裂构造样式(构造位置见图1)
Figure 5.
图 6 西湖凹陷宁波构造某油田油气运移示意图(剖面位置见图1f)
Figure 6.
表 1 西湖凹陷地层发育及构造演化简表
Table 1. Stratigraphic and tectonic evolution of the Xihu Sag
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