滨里海盆地东缘中区块盐下构造识别方法

滨里海盆地东缘中区块在下二叠统孔谷阶沉积了巨厚的盐岩层,由于盐层速度与围岩的速度存在很大差异,造成了下伏地层在时间剖面上存在上拉现象,形成了一些假构造圈闭或者使构造幅度发生变化,成为勘探陷阱.本文针对中区块盐下构造识别的难题,分析含盐盆地速度特征和盐下构造的影响因素,提出了正演模拟、基于地震叠加速度谱的变速成图和叠前深度偏移的识别方法.综合识别结果,并相互对比验证,最终消除盐丘造成的构造假象,有效识别了盐下构造,主要目的层的平均深度误差只有1%左右.上述方法对于解决含盐盆地地区以及速度横向变化剧烈区的构造问题具有借鉴意义.

The methods of identifying sub-salt structure in central block of eastern margin of Pre-Caspian basin

There are giant thick salt domes of Permian deposited in central block of eastern margin of Pre-Caspian basin.As the huge velocity difference between salt layer and surrounding rock,the underlying strata exist pulled phenomenon in the seismic time section.It forms a number of false structural traps or structure amplitude change,which becomes the exploration traps.Aimed at the problem of sub-salt structure identification in central block,this paper analyses the velocity characteristics in salt basin and influence factors of sub-salt structure.It proposes the identification methods including seismic forward modeling,variable velocity mapping based seismic stack velocity spectrum and pre-stack depth migration.Through synthesizing recognition results and testifying each other,it eliminates sub-salt structure illusion,restores the real structural feature and effectively identifies sub-salt structure.The above methods are instructive to solve the structural problem in the salt basin or some areas with dramatic change of lateral velocity.