声反射成像测井弹性波逆时偏移方法对比研究

Comparative study on application method of elastic wave reverse time migration in acoustic reflection imaging logging

声反射成像测井中的声波逆时偏移算法在处理单分量偶极横波反射资料时可获得高精度成像结果,而面对单极声源中的多波多分量弹性波反射资料时,由于其包含PP、PS、SP和SS等多种波型分量,基于声波方程的逆时偏移处理结果中出现单反射界面对应多同相轴的偏移假象.首先在声反射成像测井中实现了纵横波耦合弹性波逆时偏移和基于Helmholtz分解的弹性波逆时偏移,在此基础上首次提出和实现了基于一阶速度-应力纵横波解耦方程的弹性波逆时偏移,通过纵横波解耦结果和成像结果对三种声反射成像测井弹性波逆时偏移进行对比研究,数值算例表明基于纵横波耦合的弹性波逆时偏移无法处理转换波(PS或SP)成像问题;Helmholtz分解虽可实现纵横波解耦但同时引起反射波振幅和相位改变,进而导致包含S波的成像分量出现极性反转问题.基于一阶速度-应力纵横波解耦方程的弹性波逆时偏移可有效处理多波多分量反射资料偏移成像,消除转换分量成像噪声,解决S波分量成像极性反转,为声反射成像测井弹性波逆时偏移算法奠定了有力的理论基础.

The Acoustic Reverse Time Migration(ARTM)in acoustic reflection imaging logging can obtain high precision imaging results when it processes single component dipole shear reflection.However,processing multi-wave multi-component monopole reflection with ARTM,which contains PP,PS,SP and SS,variety of wave mode components and so on,will result in a migration artifact of the single reflected interface corresponding to several events in the imaging results.Firstly,the Elastic Reverse Time Migration(ERTM)based on coupled P and S wave and the decoupled ERTM based on the Helmholtz decomposition are implemented in acoustic reflection imaging logging,on this basis,the ERTM based on first-order velocity-stress equation with decoupled P wave and S wave is realized for the first time.Three ERTM of acoustic reflection imaging log are studied by comparing the results of P and S wave decoupling methods and imaging results.Numerical experiments show that the ERTM based on coupled P and S wave cannot handle converted wave(PS wave or SP wave)imaging problems,the Helmholtz decomposition can decouple P and S wave,but at the same time it causes the amplitude and phase change of reflection,which leads to the polarity reversal of the imaging component including S wave.The ERTM based on the first-order velocity-stress equation with decoupled P wave and S wave can handle the problem of multi-wave multi-component reflection imaging effectively,eliminate the imaging artifacts of conversed components and S wave imaging polarity reversals,and establish a strong theoretical foundation for the ERTM in acoustic reflection imaging logging.