【摘要】 为了更好地应用地震波叠前逆时偏移成像技术,开展了逆时偏移脉冲响应研究。从有偏移距层状介质模型的脉冲响应出发,首先探讨了常规相关法逆时成像条件低频逆时噪声的成因机理,分析了上、下行波分离逆时成像条件在低频噪声压制中的优势,对比了两种逆时成像条件在偏移速度平滑条件下的脉冲响应特征;同时分析了不同偏移网格参数、速度分布等情况下地震波数值频散对逆时偏移脉冲响应精度的影响。计算结果表明,地震波波场延拓过程中相对波阻抗差界面的上行反射波场是逆时背景噪声的主要成因;速度平滑能够有效降低低频背景噪声,但以牺牲成像位置准确性为代价;地震波数值频散是影响逆时成像精度的一个重要因素,逆时偏移参数的选择必须严格依据数值频散关系。与此同时,还通过模型验证了逆时偏移中震源和检波点位置具有可互换性,为共检波点道集的逆时偏移处理提供了方法指导。通过逆时偏移参数的优选,在实际陆上地震资料叠前逆时偏移中取得了较好的成像效果。更多还原

【Abstract】 In order to better apply the seismic wave prestack reverse-time migration technology,we studied the impulse response of reverse-time migration.Starting from the impulse response of layered media model with offset,firstly,we discuss the genesis of low-frequency reverse-time noise of the conventional correlation reverse-time imaging conditions,analyze the advantages of the reverse-time migration conditions in up-going and down-going wavefield separation for suppressing low-frequency noise,and compare the impulse responses in the above two reverse-time migration conditions with smoothed migration velocity.Then,we analyze the influence of seismic wave numerical dispersion on the accuracy of the reverse-time migration impulse response under the conditions of different migration grid parameters and velocity distribution.The computational results show that the reverse-time background noise is mainly caused by the up-going reflection wavefield corresponding to the relative wave impedance difference interface during wavefield continuation.Velocity smooth can effectively reduce low-frequency background noise while decrease the accuracy of imaging.Seismic wave numerical dispersion is one of the important factors affecting the accuracy of reverse-time migration,and the selection of reserve-time migration parameters must be extremely obey the numerical dispersion relationship.Meanwhile,model testing proves the interchangeability of source and receiving point in reserve-time migration,which provides method guide for reserve-time migration.By optimizing reserve-time migration parameters,application on actual land data obtains good imaging result.更多还原