走滑-伸展应力区高速异常带特征、成因及定量刻画——以渤海湾盆地莱北低凸起明下段为例

伸展应力和走滑剪切应力共同控制莱北低凸起的形成和演化,在钻探过程中发现该区横向速度变化较大,严重影响了钻前深度预测和后续滚动勘探。为此,利用测井资料、三维地震资料和地震速度资料研究了莱北低凸起走滑-伸展应力区的高速异常现象。基于区域应力场机制及压实量分析,讨论了构造对地层速度的横向控制作用,探索了高速异常的成因,利用"去除正常压实作用"的方法定量刻画了高速异常带。结果表明:①在走滑-伸展应力区,受次级挤压分量产生的水平挤压作用影响,雁列式T破裂带内部地层除了存在垂向正常压实作用之外,还存在水平构造压实作用——莱北低凸起浅层NE向高速异常带的成因;②高速异常带沿着雁列式T破裂展布,其分布范围受断裂活动范围控制,高速异常量与断层的活动强度具有较强的正相关性,与高速异常带的发育规律吻合。

Characteristics,genesis and quantitative characterization of high-velocity anomaly zone in strike-slip and extensional stress zone:a case from Lower Member of Minghuazhen Formation of Laibei Low Uplift in the Bohai Bay Basin

Extensional stress and strike-slip shear stress jointly control the formation and evolution of the Laibei Low Uplift. It is found during drilling that the lateral velocity changes greatly, which seriously affects pre-drilling depth prediction and following progressive exploration. Therefore, logging data, 3D seismic data and seismic velocity data are used to study the high-velocity anomaly in the strike-slip and extensional stress zone of Laibei Low Uplift. After the analysis of the regional stress field mechanism and the compaction amount, this paper discusses the control effect of structure on the lateral variation of velocity and the cause of the high-velocity anomaly. The method of removing normal compaction is utilized to quantitatively describe the high-velocity anomaly zone. The results show the followings: ①In the strike-slip and extensional stress zone, the internal strata of the en echelon T fracture zone are affected by not only vertical normal compaction but also horizontal tectonic compression produced by the secondary compression component. The horizontal tectonic compression is the cause of the shallow NE-trending high-velocity anomaly zone in the Laibei Low Uplift. ②The high-velocity anomaly zone spreads along the en echelon T fracture, and its distribution is controlled by the range of fault activities. Besides, the amount of high-velocity anomaly and the fault activity intensity have a strong positive correlation, which is consistent with the development law of the high-velocity anomaly zone.