声介质波动方程反射旅行时反演方法

储层精细描述需要精准的背景速度场,全波形反演(FWI)能求取浅层速度场高波数成分。透射波和折射波一般具有较大入射角孔径,可用来恢复速度模型的长波长分量;反射波仅有较小反射角孔径,通常用于恢复速度场短波长分量。本文利用偏移/反偏移算子从背景速度场获取反射波信息,推导了反射波路径;进而得到了波动方程反射层析梯度公式;反演过程中结合Ma和Luo的思路改进了反射层析中伴随源的形式,并修改了梯度的计算;运用动态图像校正法计算反射波旅行时差,实现了利用反射波信息反演速度场低波数成分。模型试算结果表明,本文方法能提高反演的稳定性,具有更好应用潜力。

Wave equation reflection travel-time inversion in acoustic media

The key of reservoir characterization needs accurate background velocity field. Full waveform inversion(FWI) can recover higher wave number information of shallow layers. Transmitted wave and refracted wave usually have a larger incidence angle aperture; they can be used to recover the long wavelength components of the velocity model. While reflections have narrow incidence angle aperture, they are used to recover short wavelength components. Therefore, we rebuilt the reflections gradient to recover velocity model long wavelength components. We get reflections from the background velocity field using migration and demigration operators and construct the reflected wave paths. Then we establish a gradient formula of wave equation reflection travel-time inversion. During inversion process, we combine the ideas of Ma and Luo to improve the form of adjoint sources. We also modify the gradient formulation. Simultaneously dynamic image warping method is used for the time lag calculation between reflections. Finally we achieve a low wavenumber components inversion of velocity model using reflected wave information. Model tests demonstrate better stability and application potentiality of the proposed method.