低秩动态匹配约束下的反射波走时反演

反射波走时反演兼具走时反演与反射波形反演的低波数特征, 对与走时相关的地下大尺度背景信息具有较好的更新能力。走时反演时移量的准确估算是反射波走时反演的关键点。传统全局时延互相关可有效估计全局时移量, 但难以准确描述地震道的局部非稳态时移特征且单道估计容易造成空间连续性较差的问题。为此, 综合考虑反射波走时反演伴随源的空间连续性及时间非稳态特征, 引入低秩近似和动态图像估计, 构建低秩动态匹配约束算法, 以增强时差估计结果的时间非稳态性及空间连续性。实验结果表明, 相比单纯采用动态图像估计得到的时差剖面, 低秩动态匹配约束结果具有更好的多维度稳定性, 反演梯度横向连续性更好, 更符合地质沉积的结构特征, 反演结果连续性更优。利用低秩动态匹配约束下的结果作为初始模型的全波形反演及逆时偏移成像结果均证明了方法的有效性。

Reflection travel-time inversion is characterized by a low wavenumber for both travel-time and reflection waveform inversion.Moreover, because only travel-time is used instead of amplitude, it can effectively reduce the requirement for accurate reflection in the reverse migration process of traditional reflection waveform inversion.Hence, the number of inversion calculations is significantly reduced.An accurate estimation of the time shift is the key to reflection travel-time inversion.Traditional methods based on channel correlation can effectively estimate global time-shift features; however, it is difficult to accurately estimate the local unsteady time-shift features of seismic channels.In addition, a single-channel estimation can easily result in poor transverse continuity.To enhance the vertical resolution and horizontal continuity of the reflection travel-time inversion, this study considered multidimensional continuity and instability, introduced a low-rank approximation and dynamic image estimation, and constructed a low-rank dynamic matching constraint.The experimental results showed that, compared with the time difference profiles obtained using only dynamic image estimation, the low-rank dynamic matching constraint constructed in this study had better stability in the vertical and horizontal directions, lateral continuity of inverse gradients, consistency with the structural characteristics of geological deposits, and continuity of inversion results.Using the results of this study as the initial model, the full waveform inversion and reverse time-migration imaging results proved the effectiveness of the method.