近地表速度模型精度影响分析

Analysis of near-surface velocity model accuracy influence

地震成像是地震勘探工作的重点和难点,而速度场的精度是地震成像的关键。为了探讨双复杂条件下近地表速度场对地震偏移成像的影响,依据弹性波动方程正演模拟的数据,在给定不同误差的近地表速度模型条件下,对比叠前深度偏移后近地表速度模型精度对线性噪声压制、浅层成像质量和精度的影响。研究结果表明,当风化层厚度误差大于+20%或风化层速度误差小于-30%时,叠前深度偏移剖面浅层反射特征趋于复杂化,层位埋深误差较大;风化层厚度为负误差或风化层速度为正误差的情况下,相对而言对偏移结果影响较小;相同比例的误差,风化层厚度的正误差比负误差对成像精度的影响大,风化层速度的负误差比正误差对成像精度的影响大。该研究对浅表层速度建模具有较为针对性地指导意义。

Seismic imaging is the focal and difficult point in seismic exploration,and the accuracy of velocity field is the key of seismic imaging.In order to explore the influence of velocity field on seismic migration imaging under double complex conditions,a seismic velocity model is established according to the actual seismic and geological data.In order to explore the influence of near-surface velocity field on seismic migration imaging under double complex conditions,according to the data from forward modeling of elastic wave equation and given near-surface velocity models with different errors,compared the effects of near-surface velocity model accuracy on linear noise suppression,imaging quality and accuracy in shallow layer after prestack depth migration.The results show that when the thickness error of weathered layer is greater than+20%or the velocity error is less than-30%,the shallow reflection characteristics of prestack depth migration section tend to be complex,and the buried depth error is larger;When the thickness error of weathered layer is negative or the velocity error is positive,it has less influence on the migration results;With the same proportion of error,the positive error of weathered layer thickness has a greater impact on the imaging accuracy than the negative error;the negative error of weathered layer velocity has a greater impact on imaging accuracy than the positive error.It has targeted guiding significance for velocity modeling of shallow layer.