摘要
“断层阴影”是复杂断块区地震成像面临的经典问题.尼日尔Termit盆地属中西非裂谷系中典型的中新生代裂谷盆地,其时间域地震剖面上,平行盆地长轴方向的大断层下盘普遍存在断层阴影效应,给地震资料处理解释带来挑战的同时,也为系统开展复杂断块区断层阴影特征、识别与消除研究提供了极佳案例.本文根据Termit盆地地层结构及速度特征,建立了研究区断层模型,通过正演模拟系统地测试了层速度、断层断距及倾角等物性和几何参数对断层阴影特征的影响,结果表明地层速度差和断距大小是影响同相轴畸变的主要因素,且它们与畸变量之间呈正相关;断层倾角对畸变量没有影响,但影响畸变的横向范围且两者之间呈负相关.由于断层阴影之间的组合、叠加效应,在时间偏移剖面上会导致出现次级断垒、断背斜及断层下伏地层构造高点偏移等构造假象;结合地层建模和正演模拟,可以对断层阴影导致的此类构造假象进行有效识别.根据Termit盆地不同工区的前期资料积累情况,我们灵活采用走时定量补偿校正、变速时深转换成图及叠前深度偏移等技术压制和消除断层阴影,取得了良好效果,显著提高了研究区大断层下伏构造的落实程度,不仅为Termit盆地油田勘探开发提供了技术支撑,也为其他地区裂谷系盆地断层阴影研究提供了有益借鉴.
The fault shadow is the zone where the seismic events in the footwall of a fault are seriously dislocated or distorted in a timedomain seismic section,and thus the seismic imaging is unreliable for the subsequent geological interpretation.In the timedomain seismic sections acquired in the Termit Basin,Niger,the fault shadows prevail for the imaging of the footwalls of large fault blocks.Although the appearance of the fault shadows is a challenge for the data processing and interpretation,it provides a good case to investigate their nature and characteristics,and to develop the strategies to recognize and eliminate the fault shadows effectively.In this paper,the geological models of the fault blocks were built based on the constraints of the stratigraphic architecture and physical properties of the strata in the Termit Basin.And then,the forward modeling was carried out to recognize the effects on the fault shadows derived from the interval velocity,fault throw and dip angle of the normal fault,respectively.The tests demonstrate that both the interval velocity and the fault throw dominate the values of abnormal traveltimes of the fault shadow by a positive correlation with either of them.However,the dip angle of the normal fault has no impact on the values of abnormal traveltimes but dominates the lateral extent of the fault shadow by a negative correlation.In addition,the tests also show that the combination and/or superposition of the sets of fault shadows would subsequently induce the pseudo tectonic structures,such as the subhorst,subfaulted anticline,and even led to the considerably lateral offset of the trap\s roof.Fortunately,these pseudotectonic substructures could be recognized by the forward modeling and geological analyses.Finally,the traveltime compensation,variable timedepth conversation and prestack depth migration methods were flexibly applied into the seismic data processing acquired in the Termit Basin.The problems related to the fault shadow were resolved successfully,which provides a good example for the other rifting basins in Africa.
作者
孙维昭
王中凡
张智
SUN WeiZhao;WANG ZhongFan;ZHANG Zhi(Geophysical Research Institute of BGP Inc.,CNPC,Zhuozhou 072750,China;Guilin University of Technology,Guilin 541004,China)
出处
《地球物理学进展》
CSCD
北大核心
2022年第4期1593-1604,共12页
Progress in Geophysics
基金
国家自然科学基金面上项目(41904048)资助
