利用独立伽马场的反射波时间比例转换波叠前时间偏移

基于转换波时间比例的转换波叠前时间偏移方法不利于纵波和横波速度分析,也无法保证后续偏移成像的精度。对比分析了转换波和反射波时间比例表征的两种转换波叠前时间偏移方法,指出基于反射波时间比例的转换波叠前时间偏移方法可直接引用由反射波数据求取的纵波速度,将双平方根时间方程的求解简化为单独求取横波速度问题,有效地降低不确定性;在反射波时间比例的表征中引入独立伽马变量,给出利用独立伽马场的转换波叠前时间偏移方法,通过时间匹配求取介质纵横波平均速度比,消除炮检距、地层倾角等因素的影响,在此基础上迭代计算横波速度并更新纵波速度,得到具有明显物理意义的纵波速度、横波速度和介质纵横波平均速度比。实际数据应用表明,该方法具有更高的运算效率和更好的成像效果。

Prestack time migration based on a convented wave time scale isn’t suitable for P-wave and S-wave velocity analysis and can’t ensure the imaging accuracy.Prestack time migration for converted wave can be realized according to the converted wave time scale or the reflection time scale.Both methods were compared and analyzed.The method using reflection time scale directly quotes the P-wave velocity obtained from reflection data,and the double square root time formula can be simplified to a separate problem for calculating the S-wave velocity,so as to effectively reduce the uncertainty.We introduce the independent gamma to the course of prestack time migration for a converted wave based on the reflection time scale;the P-wave and S-wave average velocity ratio can be acquired by time matching,accordingly.It can eliminate the effects of the offset,stratigraphic dip and other factors.On this basis,we calculated the S-wave velocity iteratively and updated the P-wave velocity continuously,and the P-wave velocity,S-wave velocity,and P-and S-wave average velocity ratio can be obtained with clear physical meaning.The practical application shows that the method has high computational efficiency and good imaging effect.

国家科技重大专项(2016ZX05027-002)资助。