如何消除巨厚盐岩对下伏地层构造解释的影响

How to eliminate the influence of thick salt rock on structural interpretation of underlying formation

也门69区块隶属于马里卜-夏布瓦盆地,盆地内侏罗系萨巴特恩组以盐岩发育为特征,盐岩沉积广泛,厚度巨大。由于盐岩和下伏地层速度的差异较大,又由于高速盐丘的分布及其厚度变化差异性较大,造成盐丘厚度越大,巨厚盐岩下伏地层的构造上拉幅度一般也越大,致使构造面积和幅度变大,或者出现假构造;同时,盐丘翼部或盐丘之间则出现地层下拉现象,使得具有一定面积和幅度的圈闭消失,盐下地层地震反射存在构造假象,影响了进一步的勘探部署。文中试图以高速巨厚盐丘分布及其厚度变化对下伏地层构造影响为主线,分析盐岩厚度与盐下地层上拉幅度的关系;建立三维速度场,利用变速作图思想进行时间深度转换,利用地震正演技术验证速度分析和时间深度转换成果的可信度,获得研究区盐下地层真实的构造解释成果。

Block 69 in Yemen belongs to Marib-Shabwah Basin.Salt rock was developed in Jurassic Sabatayn Formation in the basin,with salt rock deposition extensive and thickness tremendous.Because the differences of salt rock and underlying formation velocity and the differences of high-speed salt dome distribution and its thickness change are great,which causes that the thicker the salt dome is,the greater the pull-up amplitude of salt structure of underlying formation is,and results in the enlarged structural area and amplitude,or causes the present of pseudo-structure.At same time,the pull-down phenomenon of formation at salt dome flank or among salt domes makes the trap with definite area and amplitude disappear.The existence of structure pseudomorph of subsalt formation seismic reflection affects the further exploration disposition.This paper analyzes the relationship between the salt rock thickness and the pull-up amplitude of subsalt formation based on the influence of high-speed thick salt dome distribution and its thickness change on underlying formation structure.The actual structure of subsalt formation has been identified through establishing the three-dimensional velocity field and through using the variable velocity mapping to conduct the time-depth conversion and using the seismic forward to verify the credibility of velocity analysis and time-depth conversion results.