西湖凹陷天台斜坡带北部构造变换带特征及油气地质意义

天台斜坡带北部紧邻平湖斜坡带平湖油气田，是西湖凹陷重要的油气勘探接替区。通过西湖凹陷天台斜坡带北部构造特征梳理，解析构造变换带样式、演变，并探讨其油气地质意义。研究结果表明，在结构特征上，天台斜坡带北部构造变换带整体处于NWW向基底舟山-国头断裂带上，是凹陷“南北分块”的重要体现，发育有独特的反向断阶；在构造样式上，天台斜坡带北部扭动变换断裂组合可分为北段缓冲式和南段传递式两个次级变换区，顺NWW向基底断裂的扭动变换作用南强北弱，在断裂组合上分别表现为“网格式”和“马尾式”；在成因演化上，天台斜坡带北部构造变换在早期伸展断陷及后期挤压反转中均有发育，自下而上具有持续递进的演变特征，调节南北两侧NE-NNE向断裂系伸展和挤压强度的差异，并使部分断裂改变原有的延伸方向。天台斜坡带北部与构造变换作用相关的断裂组合不仅利于控制各类扭动圈闭的发育，也利于油气顺扭动相关断裂垂向运移充注，此外，在构造变换带控制背景下该区亦是有利的前平湖组优质砂体富集区带。

Characteristics of the structural transfer zone of northern Tiantai slope in Xihu Sag of the East China Sea Basin and their petroleum geological significances

The northern Tiantai slope of the Xihu Sag, next to the Pinghu oil and gas field, is an important exploration target for future replacement. After a through review of the structural characteristics of the slope, this paper is devoted to the analysis of structural styles and evolutionary process of the transfer zone and their significance to petroleum accumulation. The results show that, in terms of structural characteristics, the structural transfer zone of the northern Tiantai Slope is developed upon the NWW Zhoushan-Guotou basement fault zone under the control of the “North-south Blocking”, where a special reverse fault terrace occurs. The northern Tiantai slope can be further divided into two secondary transfer types: the buffering type in the north and the transferring in the south. The torsional transfer structure, along the NWW basement fault, is strong in the south but weak in the north, which is called the faults of "reticulation type" and "horsetail type" respectively in this paper in view of the fault combination. In terms of genetic evolution, the structural transfer zone of the northern Tiantai Slope is developed in the early period of fault subsiding up to late compression and reversal period, showing a continuous and progressive evolutionary process, which adjusts the difference of extension and compression strength of NE-NNE fault system between the north and the south and by which the original extension direction of some faults is changed. Finally, it is revealed that the fault combination under the control of structural transfer in the northern Tiantai slope area is not only favorable to the forming of various twisted trap, but also favorable to the vertical migration and recharge of oil-gas along the twisted faults. Under the control of structural transfer zone, the northern Tiantai slope is also a favorable area for the deposition of Pre-Pinghu high-quality sandy deposits.