西湖凹陷杭州斜坡构造差异及其对成藏的影响

Structural Differences and Impacts on Hydrocarbon Accumulation in Hangzhou Slope of Xihu Sag

杭州斜坡是西湖凹陷油气勘探的新区,构造特征的研究是开展石油地质条件研究的基础。通过对杭州斜坡的结构、主控断裂的演化及其对油气运移控制作用的分析,探讨了斜坡结构差异及其对油气成藏的影响。研究结果表明:杭州斜坡分为北段、中段和南段三个部分,中段断层走向为北北东向,单个断层的延伸长度小但数量多,存在倾向东和倾向西的顺向断层和反向断层。迎翠轩主断裂在平湖组沉积时期持续活动,杭州斜坡中段在平湖组中段下部沉积时期断层活动最强,最大落差达800 m。迎翠轩主断层走向变化、断层两侧砂岩含量和岩性反演结果表明,杭州斜坡中段断层上升盘的砂体发育程度较北段差,封堵性优于北段。关键成藏期(23 Ma和12 Ma)杭州斜坡中段处在有利的油气运移通道之上,迎翠轩主断裂中段在15Ma后基本不活动,有利于下降盘的油气聚集。

The Hangzhou slope is a frontier for oil and gas exploration in the Xihu sag.Structural characteristics are the basis for petroleum geological study.Based on the structures of the Hangzhou slope,the evolution of main controlling faults and their controls on hydrocarbon migration,we analyze the structural differences of slopes and their effects on hydrocarbon accumulation.The results show that the Hangzhou slope is divided into three parts:the northern,middle,and southern part.The strike direction of the faults in the middle section is.NNE,and individual faults are small but numerous.There are E-dipping normal faults and W-dipping reverse faults.The Yingcuixuan main fault may have been active during the sedimentation of the Pinghu Formation,and the middle part of the Hangzhou slope had the strongest fault activity with maximum drop of 800 m,during the sedimentation of the lower part of the Pinghu Formation.The fault strike change,the sandstone content,and the lithological inversion around the main fault suggest that the sandbody is not well developed in the Yingcuixuan main fault's upthrow wall in the middle part of the Hangzhou slope,whose sealing is better than that in the northern part.During the key accumulation periods(ca.23 Ma and 12 Ma),the middle section of the Hang-zhou slope was on the favorable oil and gas migration pathway.The middle part of Yingcuixuan main fault is in active after 15 Ma,which enriches the oil and gas in the downthrow wall.